If the user has asked for the vertical height registers to be recomputed
by setting bit 15 in the video mode number, we do so without clearing the
Protect bit in the Vertical Retrace Register before setting the Overflow
register.  As a result, if the VGA BIOS had set the Protect bit, the
write to the Overflow register will be dropped, and bits [9:8] of the
vertical height will be left unchanged.

This is a bug imported from the assembly version of this code.  It was
pointed out by Etienne Lorrain.

Cc: Etienne Lorrain <etienne_lorrain@yahoo.fr>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Fix incorrect assembly constraints.  In particular, fix memory
constraints used inside push..pop, which can cause invalid operation
since gcc may generate %esp-relative references.

Additionally:

outl() should have "dN" not "dn".

query_mca() shouldn't listen 16/32-bit registers in an 8-bit only
context.

has_eflag(): the "mask" is only used well after both the stack pointer
and the output registers have been touched; this requires the output
registers to be earlyclobbers (=&) and the input to exclude memory (so
"ri", not "g").

Thanks to Etienne Lorrain and Chuck Ebbert for prompting this review.

Cc: Etienne Lorrain <etienne_lorrain@yahoo.fr>
Cc: Chuck Ebbert <cebbert@redhat.com>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Correct a comment in arch/i386/boot/build/tools.c; we now build the
kernel from only two components instead of three, since the boot
sector has been integrated in the setup code.
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Document the existence of a published git tree for the x86 setup code.
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

* 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4:
  ext4: extent macros cleanup
  Fix compilation with EXT_DEBUG, also fix leXX_to_cpu conversions.
  ext4: remove extra IS_RDONLY() check
  ext4: Use is_power_of_2()
  Use zero_user_page() in ext4 where possible
  ext4: Remove 65000 subdirectory limit
  ext4: Expand extra_inodes space per the s_{want,min}_extra_isize fields 
  ext4: Add nanosecond timestamps
  jbd2: Move jbd2-debug file to debugfs
  jbd2: Fix CONFIG_JBD_DEBUG ifdef to be CONFIG_JBD2_DEBUG
  ext4: Set the journal JBD2_FEATURE_INCOMPAT_64BIT on large devices
  ext4: Make extents code sanely handle on-disk corruption
  ext4: copy i_flags to inode flags on write
  ext4: Enable extents by default
  Change on-disk format to support 2^15 uninitialized extents
  write support for preallocated blocks
  fallocate support in ext4
  sys_fallocate() implementation on i386, x86_64 and powerpc

* 'upstream' of git://git.infradead.org/~dedekind/ubi-2.6: (28 commits)
  UBI: fix compile warning
  UBI: fix error handling in erase worker
  UBI: fix comments
  UBI: remove unneeded error checks
  UBI: cleanup usage of try_module_get
  UBI: fix overflow bug
  UBI: bugfix in max_sqnum calculation
  UBI: bugfix in sqnum calculation
  UBI: fix signed-unsigned multiplication
  UBI: fix bug in atomic_leb_change()
  UBI: fix message
  UBI: fix debugging stuff
  UBI: bugfix in error path
  UBI: use is_power_of_2()
  UBI: fix freeing ubi->vtbl while unloading
  UBI: fix MAINTAINERS
  UBI: bugfix in ubi_leb_change()
  UBI: kill homegrown endian macros
  UBI: cleanup ioctl handling
  UBI: error path bugfix
  ...

* 'master' of master.kernel.org:/pub/scm/linux/kernel/git/davem/net-2.6: (24 commits)
  [NETFILTER]: xt_connlimit needs to depend on nf_conntrack
  [NETFILTER]: ipt_iprange.h must #include <linux/types.h>
  [IrDA]: Fix IrDA build failure
  [ATM]: nicstar needs virt_to_bus
  [NET]: move __dev_addr_discard adjacent to dev_addr_discard for readability
  [NET]: merge dev_unicast_discard and dev_mc_discard into one
  [NET]: move dev_mc_discard from dev_mcast.c to dev.c
  [NETLINK]: negative groups in netlink_setsockopt
  [PPPOL2TP]: Reset meta-data in xmit function
  [PPPOL2TP]: Fix use-after-free
  [PKT_SCHED]: Some typo fixes in net/sched/Kconfig
  [XFRM]: Fix crash introduced by struct dst_entry reordering
  [TCP]: remove unused argument to cong_avoid op
  [ATM]: [idt77252] Rename CONFIG_ATM_IDT77252_SEND_IDLE to not resemble a Kconfig variable
  [ATM]: [drivers] ioremap balanced with iounmap
  [ATM]: [lanai] sram_test_word() must be __devinit
  [ATM]: [nicstar] Replace C code with call to ARRAY_SIZE() macro.
  [ATM]: Eliminate dead config variable CONFIG_BR2684_FAST_TRANS.
  [ATM]: Replacing kmalloc/memset combination with kzalloc.
  [NET]: gen_estimator deadlock fix
  ...

* 'master' of master.kernel.org:/pub/scm/linux/kernel/git/davem/sparc-2.6:
  [SPARC64]: Set vio->desc_buf to NULL after freeing.
  [SPARC]: Mark sparc and sparc64 as not having virt_to_bus
  [SPARC64]: Fix reset handling in VNET driver.
  [SPARC64]: Handle reset events in vio_link_state_change().
  [SPARC64]: Handle LDC resets properly in domain-services driver.
  [SPARC64]: Massively simplify VIO device layer and support hot add/remove.
  [SPARC64]: Simplify VNET probing.
  [SPARC64]: Simplify VDC device probing.
  [SPARC64]: Add basic infrastructure for MD add/remove notification.

* 'xen-upstream' of ssh://master.kernel.org/pub/scm/linux/kernel/git/jeremy/xen: (44 commits)
  xen: disable all non-virtual drivers
  xen: use iret directly when possible
  xen: suppress abs symbol warnings for unused reloc pointers
  xen: Attempt to patch inline versions of common operations
  xen: Place vcpu_info structure into per-cpu memory
  xen: handle external requests for shutdown, reboot and sysrq
  xen: machine operations
  xen: add virtual network device driver
  xen: add virtual block device driver.
  xen: add the Xenbus sysfs and virtual device hotplug driver
  xen: Add grant table support
  xen: use the hvc console infrastructure for Xen console
  xen: hack to prevent bad segment register reload
  xen: lazy-mmu operations
  xen: Add support for preemption
  xen: SMP guest support
  xen: Implement sched_clock
  xen: Account for stolen time
  xen: ignore RW mapping of RO pages in pagetable_init
  xen: Complete pagetable pinning
  ...

This reverts commit 5a26f6bb.

The original patch causes boot failures when built with ppc64_defconfig.  The
quickest fix is to revert it while alterates are investigated.
Signed-off-by: NTony Breeds <tony@bakeyournoodle.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This fixes the fallout from the recent powerpc merge (commit
489de302):

   CC      arch/powerpc/kernel/pci-common.o
  arch/powerpc/kernel/pci-common.c:160: error: conflicting types for 'pcibios_add_platform_entries'
  include/linux/pci.h:889: error: previous declaration of 'pcibios_add_platform_entries' was here
Signed-off-by: NTony Breeds <tony@bakeyournoodle.com>
Tested-by: NBret Towe <magnade@gmail.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

A domU Xen environment has no non-virtual drivers, so make sure
they're all disabled at once.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>

Most of the time we can simply use the iret instruction to exit the
kernel, rather than having to use the iret hypercall - the only
exception is if we're returning into vm86 mode, or from delivering an
NMI (which we don't support yet).

When running native, iret has the behaviour of testing for a pending
interrupt atomically with re-enabling interrupts.  Unfortunately
there's no way to do this with Xen, so there's a window in which we
could get a recursive exception after enabling events but before
actually returning to userspace.

This causes a problem: if the nested interrupt causes one of the
task's TIF_WORK_MASK flags to be set, they will not be checked again
before returning to userspace.  This means that pending work may be
left pending indefinitely, until the process enters and leaves the
kernel again.  The net effect is that a pending signal or reschedule
event could be delayed for an unbounded amount of time.

To deal with this, the xen event upcall handler checks to see if the
EIP is within the critical section of the iret code, after events
are (potentially) enabled up to the iret itself.  If its within this
range, it calls the iret critical section fixup, which adjusts the
stack to deal with any unrestored registers, and then shifts the
stack frame up to replace the previous invocation.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>

arch/i386/xen/xen-asm.S defines some small pieces of code which are
used to implement a few paravirt_ops.  They're designed so they can be
used either in-place, or be inline patched into their callsites if
there's enough space.

Some of those operations need to make calls out (specifically, if you
re-enable events [interrupts], and there's a pending event at that
time).  These calls need the call instruction to be relocated if the
code is patched inline.  In this case xen_foo_reloc is a
section-relative symbol which points to xen_foo's required relocation.

Other operations have no need of a relocation, and so their
corresponding xen_bar_reloc is absolute 0.  These are the cases which
are triggering the warning.

This patch adds those symbols to the list of safe abs symbols.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Cc: Adrian Bunk <bunk@stusta.de>

This patchs adds the mechanism to allow us to patch inline versions of
common operations.

The implementations of the direct-access versions save_fl, restore_fl,
irq_enable and irq_disable are now in assembler, and the same code is
used for both out of line and inline uses.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Keir Fraser <keir@xensource.com>

An experimental patch for Xen allows guests to place their vcpu_info
structs anywhere.  We try to use this to place the vcpu_info into the
PDA, which allows direct access.

If this works, then switch to using direct access operations for
irq_enable, disable, save_fl and restore_fl.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Keir Fraser <keir@xensource.com>

The guest domain can be asked to shutdown or reboot itself, or have a
sysrq key injected, via xenbus.  This patch adds a watcher for those
events, and does the appropriate action.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Cc: Chris Wright <chrisw@sous-sol.org>

Make the appropriate hypercalls to halt and reboot the virtual machine.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Acked-by: NChris Wright <chrisw@sous-sol.org>

The network device frontend driver allows the kernel to access network
devices exported exported by a virtual machine containing a physical
network device driver.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: NChris Wright <chrisw@sous-sol.org>
Acked-by: NJeff Garzik <jeff@garzik.org>
Cc: Ian Pratt <ian.pratt@xensource.com>
Cc: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Cc: Stephen Hemminger <shemminger@linux-foundation.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Keir Fraser <Keir.Fraser@cl.cam.ac.uk>
Cc: netdev@vger.kernel.org

The block device frontend driver allows the kernel to access block
devices exported exported by a virtual machine containing a physical
block device driver.
Signed-off-by: NIan Pratt <ian.pratt@xensource.com>
Signed-off-by: NChristian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: NChris Wright <chrisw@sous-sol.org>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Greg KH <greg@kroah.com>
Cc: Jens Axboe <axboe@kernel.dk>

This communicates with the machine control software via a registry
residing in a controlling virtual machine. This allows dynamic
creation, destruction and modification of virtual device
configurations (network devices, block devices and CPUS, to name some
examples).

[ Greg, would you mind giving this a review?  Thanks -J ]
Signed-off-by: NIan Pratt <ian.pratt@xensource.com>
Signed-off-by: NChristian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: NChris Wright <chrisw@sous-sol.org>
Cc: Greg KH <greg@kroah.com>

Add Xen 'grant table' driver which allows granting of access to
selected local memory pages by other virtual machines and,
symmetrically, the mapping of remote memory pages which other virtual
machines have granted access to.

This driver is a prerequisite for many of the Xen virtual device
drivers, which grant the 'device driver domain' restricted and
temporary access to only those memory pages that are currently
involved in I/O operations.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: NIan Pratt <ian.pratt@xensource.com>
Signed-off-by: NChristian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: NChris Wright <chrisw@sous-sol.org>

Implement a Xen back-end for hvc console.

* * *
Add early printk support via hvc console, enable using
"earlyprintk=xen" on the kernel command line.

From: Gerd Hoffmann <kraxel@suse.de>
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: NChris Wright <chrisw@sous-sol.org>
Acked-by: NIngo Molnar <mingo@elte.hu>
Acked-by: NOlof Johansson <olof@lixom.net>

The hypervisor saves and restores the segment registers as part of the
state is saves while context switching.  If, during a context switch,
the next process doesn't use the TLS segments, it invalidates the GDT
entry, causing the segment register reload to fault.  This fault
effectively doubles the cost of a context switch.

This patch is a band-aid workaround which clears the usermode %gs
after it has been saved for the previous process, but before it gets
reloaded for the next, and it avoids having the hypervisor attempt to
erroneously reload it.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: NChris Wright <chrisw@sous-sol.org>

This patch uses the lazy-mmu hooks to batch mmu operations where
possible.  This is primarily useful for batching operations applied to
active pagetables, which happens during mprotect, munmap, mremap and
the like (mmap does not do bulk pagetable operations, so it isn't
helped).
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Acked-by: NChris Wright <chrisw@sous-sol.org>

Add Xen support for preemption.  This is mostly a cleanup of existing
preempt_enable/disable calls, or just comments to explain the current
usage.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: NChris Wright <chrisw@sous-sol.org>

This is a fairly straightforward Xen implementation of smp_ops.

Xen has its own IPI mechanisms, and has no dependency on any
APIC-based IPI.  The smp_ops hooks and the flush_tlb_others pv_op
allow a Xen guest to avoid all APIC code in arch/i386 (the only apic
operation is a single apic_read for the apic version number).

One subtle point which needs to be addressed is unpinning pagetables
when another cpu may have a lazy tlb reference to the pagetable. Xen
will not allow an in-use pagetable to be unpinned, so we must find any
other cpus with a reference to the pagetable and get them to shoot
down their references.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: NChris Wright <chrisw@sous-sol.org>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Andi Kleen <ak@suse.de>

Implement xen_sched_clock, which returns the number of ns the current
vcpu has been actually in an unstolen state (ie, running or blocked,
vs runnable-but-not-running, or offline) since boot.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Acked-by: NChris Wright <chrisw@sous-sol.org>
Cc: john stultz <johnstul@us.ibm.com>

This patch accounts for the time stolen from our VCPUs.  Stolen time is
time where a vcpu is runnable and could be running, but all available
physical CPUs are being used for something else.

This accounting gets run on each timer interrupt, just as a way to get
it run relatively often, and when interesting things are going on.
Stolen time is not really used by much in the kernel; it is reported
in /proc/stats, and that's about it.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Acked-by: NChris Wright <chrisw@sous-sol.org>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Rik van Riel <riel@redhat.com>

When setting up the initial pagetable, which includes mappings of all
low physical memory, ignore a mapping which tries to set the RW bit on
an RO pte.  An RO pte indicates a page which is part of the current
pagetable, and so it cannot be allowed to become RW.

Once xen_pagetable_setup_done is called, set_pte reverts to its normal
behaviour.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Acked-by: NChris Wright <chrisw@sous-sol.org>
Cc: ebiederm@xmission.com (Eric W. Biederman)

Xen requires all active pagetables to be marked read-only.  When the
base of the pagetable is loaded into %cr3, the hypervisor validates
the entire pagetable and only allows the load to proceed if it all
checks out.

This is pretty slow, so to mitigate this cost Xen has a notion of
pinned pagetables.  Pinned pagetables are pagetables which are
considered to be active even if no processor's cr3 is pointing to is.
This means that it must remain read-only and all updates are validated
by the hypervisor.  This makes context switches much cheaper, because
the hypervisor doesn't need to revalidate the pagetable each time.

This also adds a new paravirt hook which is called during setup once
the zones and memory allocator have been initialized.  When the
init_mm pagetable is first built, the struct page array does not yet
exist, and so there's nowhere to put he init_mm pagetable's PG_pinned
flags.  Once the zones are initialized and the struct page array
exists, we can set the PG_pinned flags for those pages.

This patch also adds the Xen support for pte pages allocated out of
highmem (highpte) by implementing xen_kmap_atomic_pte.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: NChris Wright <chrisw@sous-sol.org>
Cc: Zach Amsden <zach@vmware.com>

Add a new definition for PG_owner_priv_1 to define PG_pinned on Xen
pagetable pages.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: NChris Wright <chrisw@sous-sol.org>

Put config options for Xen after the core pieces are in place.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: NChris Wright <chrisw@sous-sol.org>

Xen maintains a base clock which measures nanoseconds since system
boot.  This is provided to guests via a shared page which contains a
base time in ns, a tsc timestamp at that point and tsc frequency
parameters.  Guests can compute the current time by reading the tsc
and using it to extrapolate the current time from the basetime.  The
hypervisor makes sure that the frequency parameters are updated
regularly, paricularly if the tsc changes rate or stops.

This is implemented as a clocksource, so the interface to the rest of
the kernel is a simple clocksource which simply returns the current
time directly in nanoseconds.

Xen also provides a simple timer mechanism, which allows a timeout to
be set in the future.  When that time arrives, a timer event is sent
to the guest.  There are two timer interfaces:
 - An old one which also delivers a stream of (unused) ticks at 100Hz,
   and on the same event, the actual timer events.  The 100Hz ticks
   cause a lot of spurious wakeups, but are basically harmless.
 - The new timer interface doesn't have the 100Hz ticks, and can also
   fail if the specified time is in the past.

This code presents the Xen timer as a clockevent driver, and uses the
new interface by preference.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: NChris Wright <chrisw@sous-sol.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>

Xen implements interrupts in terms of event channels.  Each guest
domain gets 1024 event channels which can be used for a variety of
purposes, such as Xen timer events, inter-domain events,
inter-processor events (IPI) or for real hardware IRQs.

Within the kernel, we map the event channels to IRQs, and implement
the whole interrupt handling using a Xen irq_chip.

Rather than setting NR_IRQ to 1024 under PARAVIRT in order to
accomodate Xen, we create a dynamic mapping between event channels and
IRQs.  Ideally, Linux will eventually move towards dynamically
allocating per-irq structures, and we can use a 1:1 mapping between
event channels and irqs.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: NChris Wright <chrisw@sous-sol.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Eric W. Biederman <ebiederm@xmission.com>

Xen pagetable handling, including the machinery to implement direct
pagetables.

Xen presents the real CPU's pagetables directly to guests, with no
added shadowing or other layer of abstraction.  Naturally this means
the hypervisor must maintain close control over what the guest can put
into the pagetable.

When the guest modifies the pte/pmd/pgd, it must convert its
domain-specific notion of a "physical" pfn into a global machine frame
number (mfn) before inserting the entry into the pagetable.  Xen will
check to make sure the domain is allowed to create a mapping of the
given mfn.

Xen also requires that all mappings the guest has of its own active
pagetable are read-only.  This is relatively easy to implement in
Linux because all pagetables share the same pte pages for kernel
mappings, so updating the pte in one pagetable will implicitly update
the mapping in all pagetables.

Normally a pagetable becomes active when you point to it with cr3 (or
the Xen equivalent), but when you do so, Xen must check the whole
pagetable for correctness, which is clearly a performance problem.

Xen solves this with pinning which keeps a pagetable effectively
active even if its currently unused, which means that all the normal
update rules are enforced.  This means that it need not revalidate the
pagetable when loading cr3.

This patch has a first-cut implementation of pinning, but it is more
fully implemented in a later patch.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: NChris Wright <chrisw@sous-sol.org>

This patch is a rollup of all the core pieces of the Xen
implementation, including:
 - booting and setup
 - pagetable setup
 - privileged instructions
 - segmentation
 - interrupt flags
 - upcalls
 - multicall batching

BOOTING AND SETUP

The vmlinux image is decorated with ELF notes which tell the Xen
domain builder what the kernel's requirements are; the domain builder
then constructs the address space accordingly and starts the kernel.

Xen has its own entrypoint for the kernel (contained in an ELF note).
The ELF notes are set up by xen-head.S, which is included into head.S.
In principle it could be linked separately, but it seems to provoke
lots of binutils bugs.

Because the domain builder starts the kernel in a fairly sane state
(32-bit protected mode, paging enabled, flat segments set up), there's
not a lot of setup needed before starting the kernel proper.  The main
steps are:
  1. Install the Xen paravirt_ops, which is simply a matter of a
     structure assignment.
  2. Set init_mm to use the Xen-supplied pagetables (analogous to the
     head.S generated pagetables in a native boot).
  3. Reserve address space for Xen, since it takes a chunk at the top
     of the address space for its own use.
  4. Call start_kernel()

PAGETABLE SETUP

Once we hit the main kernel boot sequence, it will end up calling back
via paravirt_ops to set up various pieces of Xen specific state.  One
of the critical things which requires a bit of extra care is the
construction of the initial init_mm pagetable.  Because Xen places
tight constraints on pagetables (an active pagetable must always be
valid, and must always be mapped read-only to the guest domain), we
need to be careful when constructing the new pagetable to keep these
constraints in mind.  It turns out that the easiest way to do this is
use the initial Xen-provided pagetable as a template, and then just
insert new mappings for memory where a mapping doesn't already exist.

This means that during pagetable setup, it uses a special version of
xen_set_pte which ignores any attempt to remap a read-only page as
read-write (since Xen will map its own initial pagetable as RO), but
lets other changes to the ptes happen, so that things like NX are set
properly.

PRIVILEGED INSTRUCTIONS AND SEGMENTATION

When the kernel runs under Xen, it runs in ring 1 rather than ring 0.
This means that it is more privileged than user-mode in ring 3, but it
still can't run privileged instructions directly.  Non-performance
critical instructions are dealt with by taking a privilege exception
and trapping into the hypervisor and emulating the instruction, but
more performance-critical instructions have their own specific
paravirt_ops.  In many cases we can avoid having to do any hypercalls
for these instructions, or the Xen implementation is quite different
from the normal native version.

The privileged instructions fall into the broad classes of:
  Segmentation: setting up the GDT and the GDT entries, LDT,
     TLS and so on.  Xen doesn't allow the GDT to be directly
     modified; all GDT updates are done via hypercalls where the new
     entries can be validated.  This is important because Xen uses
     segment limits to prevent the guest kernel from damaging the
     hypervisor itself.
  Traps and exceptions: Xen uses a special format for trap entrypoints,
     so when the kernel wants to set an IDT entry, it needs to be
     converted to the form Xen expects.  Xen sets int 0x80 up specially
     so that the trap goes straight from userspace into the guest kernel
     without going via the hypervisor.  sysenter isn't supported.
  Kernel stack: The esp0 entry is extracted from the tss and provided to
     Xen.
  TLB operations: the various TLB calls are mapped into corresponding
     Xen hypercalls.
  Control registers: all the control registers are privileged.  The most
     important is cr3, which points to the base of the current pagetable,
     and we handle it specially.

Another instruction we treat specially is CPUID, even though its not
privileged.  We want to control what CPU features are visible to the
rest of the kernel, and so CPUID ends up going into a paravirt_op.
Xen implements this mainly to disable the ACPI and APIC subsystems.

INTERRUPT FLAGS

Xen maintains its own separate flag for masking events, which is
contained within the per-cpu vcpu_info structure.  Because the guest
kernel runs in ring 1 and not 0, the IF flag in EFLAGS is completely
ignored (and must be, because even if a guest domain disables
interrupts for itself, it can't disable them overall).

(A note on terminology: "events" and interrupts are effectively
synonymous.  However, rather than using an "enable flag", Xen uses a
"mask flag", which blocks event delivery when it is non-zero.)

There are paravirt_ops for each of cli/sti/save_fl/restore_fl, which
are implemented to manage the Xen event mask state.  The only thing
worth noting is that when events are unmasked, we need to explicitly
see if there's a pending event and call into the hypervisor to make
sure it gets delivered.

UPCALLS

Xen needs a couple of upcall (or callback) functions to be implemented
by each guest.  One is the event upcalls, which is how events
(interrupts, effectively) are delivered to the guests.  The other is
the failsafe callback, which is used to report errors in either
reloading a segment register, or caused by iret.  These are
implemented in i386/kernel/entry.S so they can jump into the normal
iret_exc path when necessary.

MULTICALL BATCHING

Xen provides a multicall mechanism, which allows multiple hypercalls
to be issued at once in order to mitigate the cost of trapping into
the hypervisor.  This is particularly useful for context switches,
since the 4-5 hypercalls they would normally need (reload cr3, update
TLS, maybe update LDT) can be reduced to one.  This patch implements a
generic batching mechanism for hypercalls, which gets used in many
places in the Xen code.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: NChris Wright <chrisw@sous-sol.org>
Cc: Ian Pratt <ian.pratt@xensource.com>
Cc: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Cc: Adrian Bunk <bunk@stusta.de>

Add Xen interface header files. These are taken fairly directly from
the Xen tree, but somewhat rearranged to suit the kernel's conventions.

Define macros and inline functions for doing hypercalls into the
hypervisor.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: NIan Pratt <ian.pratt@xensource.com>
Signed-off-by: NChristian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: NChris Wright <chrisw@sous-sol.org>

Add the "nosegneg" fake capabilty to the vsyscall page notes. This is
used by the runtime linker to select a glibc version which then
disables negative-offset accesses to the thread-local segment via
%gs. These accesses require emulation in Xen (because segments are
truncated to protect the hypervisor address space) and avoiding them
provides a measurable performance boost.
Signed-off-by: NIan Pratt <ian.pratt@xensource.com>
Signed-off-by: NChristian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: NChris Wright <chrisw@sous-sol.org>
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Acked-by: NZachary Amsden <zach@vmware.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Ulrich Drepper <drepper@redhat.com>

The tsc-based get_scheduled_cycles interface is not a good match for
Xen's runstate accounting, which reports everything in nanoseconds.

This patch replaces this interface with a sched_clock interface, which
matches both Xen and VMI's requirements.

In order to do this, we:
   1. replace get_scheduled_cycles with sched_clock
   2. hoist cycles_2_ns into a common header
   3. update vmi accordingly

One thing to note: because sched_clock is implemented as a weak
function in kernel/sched.c, we must define a real function in order to
override this weak binding.  This means the usual paravirt_ops
technique of using an inline function won't work in this case.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Cc: Zachary Amsden <zach@vmware.com>
Cc: Dan Hecht <dhecht@vmware.com>
Cc: john stultz <johnstul@us.ibm.com>