The new_cr3 MMU callback has been a wrapper for mmu_free_roots since commit
e676505a (KVM: MMU: Force cr3 reload with two dimensional paging on mov
cr3 emulation, 2012-07-08).

The commit message mentioned that "mmu_free_roots() is somewhat of an overkill,
but fixing that is more complicated and will be done after this minimal fix".
One year has passed, and no one really felt the need to do a different fix.
Wrap the call with a kvm_mmu_new_cr3 function for clarity, but remove the
callback.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>

The free MMU callback has been a wrapper for mmu_free_roots since mmu_free_roots
itself was introduced (commit 17ac10ad, [PATCH] KVM: MU: Special treatment
for shadow pae root pages, 2007-01-05), and has always been the same for all
MMU cases.  Remove the indirection as it is useless.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>

In commit e935b837 ("KVM: Convert kvm_lock to raw_spinlock"),
the kvm_lock was made a raw lock.  However, the kvm mmu_shrink()
function tries to grab the (non-raw) mmu_lock within the scope of
the raw locked kvm_lock being held.  This leads to the following:

BUG: sleeping function called from invalid context at kernel/rtmutex.c:659
in_atomic(): 1, irqs_disabled(): 0, pid: 55, name: kswapd0
Preemption disabled at:[<ffffffffa0376eac>] mmu_shrink+0x5c/0x1b0 [kvm]

Pid: 55, comm: kswapd0 Not tainted 3.4.34_preempt-rt
Call Trace:
 [<ffffffff8106f2ad>] __might_sleep+0xfd/0x160
 [<ffffffff817d8d64>] rt_spin_lock+0x24/0x50
 [<ffffffffa0376f3c>] mmu_shrink+0xec/0x1b0 [kvm]
 [<ffffffff8111455d>] shrink_slab+0x17d/0x3a0
 [<ffffffff81151f00>] ? mem_cgroup_iter+0x130/0x260
 [<ffffffff8111824a>] balance_pgdat+0x54a/0x730
 [<ffffffff8111fe47>] ? set_pgdat_percpu_threshold+0xa7/0xd0
 [<ffffffff811185bf>] kswapd+0x18f/0x490
 [<ffffffff81070961>] ? get_parent_ip+0x11/0x50
 [<ffffffff81061970>] ? __init_waitqueue_head+0x50/0x50
 [<ffffffff81118430>] ? balance_pgdat+0x730/0x730
 [<ffffffff81060d2b>] kthread+0xdb/0xe0
 [<ffffffff8106e122>] ? finish_task_switch+0x52/0x100
 [<ffffffff817e1e94>] kernel_thread_helper+0x4/0x10
 [<ffffffff81060c50>] ? __init_kthread_worker+0x

After the previous patch, kvm_lock need not be a raw spinlock anymore,
so change it back.
Reported-by: NPaul Gortmaker <paul.gortmaker@windriver.com>
Cc: kvm@vger.kernel.org
Cc: gleb@redhat.com
Cc: jan.kiszka@siemens.com
Reviewed-by: NGleb Natapov <gleb@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Convert the remaining couple of random shrinkers in the tree to the new
API.
Signed-off-by: NDave Chinner <dchinner@redhat.com>
Signed-off-by: NGlauber Costa <glommer@openvz.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Gleb Natapov <gleb@redhat.com>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: J. Bruce Fields <bfields@redhat.com>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Carlos Maiolino <cmaiolino@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Rientjes <rientjes@google.com>
Cc: Gleb Natapov <gleb@redhat.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: J. Bruce Fields <bfields@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Kent Overstreet <koverstreet@google.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

vcpu in page_fault_can_be_fast() is not used so remove it
Signed-off-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>

If we let L1 use EPT, we should probably also support the INVEPT instruction.

In our current nested EPT implementation, when L1 changes its EPT table
for L2 (i.e., EPT12), L0 modifies the shadow EPT table (EPT02), and in
the course of this modification already calls INVEPT. But if last level
of shadow page is unsync not all L1's changes to EPT12 are intercepted,
which means roots need to be synced when L1 calls INVEPT. Global INVEPT
should not be different since roots are synced by kvm_mmu_load() each
time EPTP02 changes.
Reviewed-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: NNadav Har'El <nyh@il.ibm.com>
Signed-off-by: NJun Nakajima <jun.nakajima@intel.com>
Signed-off-by: NXinhao Xu <xinhao.xu@intel.com>
Signed-off-by: NYang Zhang <yang.z.zhang@Intel.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

KVM's existing shadow MMU code already supports nested TDP. To use it, we
need to set up a new "MMU context" for nested EPT, and create a few callbacks
for it (nested_ept_*()). This context should also use the EPT versions of
the page table access functions (defined in the previous patch).
Then, we need to switch back and forth between this nested context and the
regular MMU context when switching between L1 and L2 (when L1 runs this L2
with EPT).
Reviewed-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: NNadav Har'El <nyh@il.ibm.com>
Signed-off-by: NJun Nakajima <jun.nakajima@intel.com>
Signed-off-by: NXinhao Xu <xinhao.xu@intel.com>
Signed-off-by: NYang Zhang <yang.z.zhang@Intel.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Inject nEPT fault to L1 guest. This patch is original from Xinhao.
Reviewed-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: NJun Nakajima <jun.nakajima@intel.com>
Signed-off-by: NXinhao Xu <xinhao.xu@intel.com>
Signed-off-by: NYang Zhang <yang.z.zhang@Intel.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

need_remote_flush() assumes that shadow page is in PT64 format, but
with addition of nested EPT this is no longer always true. Fix it by
bits definitions that depend on host shadow page type.
Reported-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Reviewed-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Since nEPT doesn't support A/D bit, so we should not set those bit
when build shadow page table.
Reviewed-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: NYang Zhang <yang.z.zhang@Intel.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

This is the first patch in a series which adds nested EPT support to KVM's
nested VMX. Nested EPT means emulating EPT for an L1 guest so that L1 can use
EPT when running a nested guest L2. When L1 uses EPT, it allows the L2 guest
to set its own cr3 and take its own page faults without either of L0 or L1
getting involved. This often significanlty improves L2's performance over the
previous two alternatives (shadow page tables over EPT, and shadow page
tables over shadow page tables).

This patch adds EPT support to paging_tmpl.h.

paging_tmpl.h contains the code for reading and writing page tables. The code
for 32-bit and 64-bit tables is very similar, but not identical, so
paging_tmpl.h is #include'd twice in mmu.c, once with PTTTYPE=32 and once
with PTTYPE=64, and this generates the two sets of similar functions.

There are subtle but important differences between the format of EPT tables
and that of ordinary x86 64-bit page tables, so for nested EPT we need a
third set of functions to read the guest EPT table and to write the shadow
EPT table.

So this patch adds third PTTYPE, PTTYPE_EPT, which creates functions (prefixed
with "EPT") which correctly read and write EPT tables.
Reviewed-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: NNadav Har'El <nyh@il.ibm.com>
Signed-off-by: NJun Nakajima <jun.nakajima@intel.com>
Signed-off-by: NXinhao Xu <xinhao.xu@intel.com>
Signed-off-by: NYang Zhang <yang.z.zhang@Intel.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

For preparation, we just move gpte_access(), prefetch_invalid_gpte(),
s_rsvd_bits_set(), protect_clean_gpte() and is_dirty_gpte() from mmu.c
to paging_tmpl.h.
Reviewed-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: NNadav Har'El <nyh@il.ibm.com>
Signed-off-by: NJun Nakajima <jun.nakajima@intel.com>
Signed-off-by: NXinhao Xu <xinhao.xu@intel.com>
Signed-off-by: NYang Zhang <yang.z.zhang@Intel.com>
Signed-off-by: NJun Nakajima <jun.nakajima@intel.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

The next patch will reuse it for other userspace exits than MMIO,
namely debug events.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Now that kvm_arch_memslots_updated() catches every increment of the
memslots->generation, checking if the mmio generation has reached its
maximum value is enough.
Signed-off-by: NTakuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Reviewed-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Currently, fast page fault incorrectly tries to fix mmio page fault when
the generation number is invalid (spte.gen != kvm.gen).  It then returns
to guest to retry the fault since it sees the last spte is nonpresent.
This causes an infinite loop.

Since fast page fault only works for direct mmu, the issue exists when
1) tdp is enabled. It is only triggered only on AMD host since on Intel host
   the mmio page fault is recognized as ept-misconfig whose handler call
   fault-page path with error_code = 0

2) guest paging is disabled. Under this case, the issue is hardly discovered
   since paging disable is short-lived and the sptes will be invalid after
   memslot changed for 150 times

Fix it by filtering out MMIO page faults in page_fault_can_be_fast.
Reported-by: NMarkus Trippelsdorf <markus@trippelsdorf.de>
Tested-by: NMarkus Trippelsdorf <markus@trippelsdorf.de>
Signed-off-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Without this information, users will just see unexpected performance
problems and there is little chance we will get good reports from them:
note that mmio generation is increased even when we just start, or stop,
dirty logging for some memory slot, in which case users cannot expect
all shadow pages to be zapped.

printk_ratelimited() is used for this taking into account the problems
that we can see the information many times when we start multiple VMs
and guests can trigger this by reading ROM in a loop for example.
Signed-off-by: NTakuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Document it to Documentation/virtual/kvm/mmu.txt
Signed-off-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Drop kvm_mmu_zap_mmio_sptes and use kvm_mmu_invalidate_zap_all_pages
instead to handle mmio generation number overflow
Signed-off-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Reviewed-by: NGleb Natapov <gleb@redhat.com>
Reviewed-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Then it has the chance to trigger mmio generation number wrap-around
Signed-off-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Reviewed-by: NGleb Natapov <gleb@redhat.com>
Reviewed-by: NMarcelo Tosatti <mtosatti@redhat.com>
[Change from MMIO_MAX_GEN - 13 to MMIO_MAX_GEN - 150, because 13 is
 very close to the number of calls to KVM_SET_USER_MEMORY_REGION
 before the guest is started and there is any chance to create any
 spte. - Paolo]
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

It is useful for debug mmio spte invalidation
Signed-off-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Reviewed-by: NGleb Natapov <gleb@redhat.com>
Reviewed-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

This patch tries to introduce a very simple and scale way to invalidate
all mmio sptes - it need not walk any shadow pages and hold mmu-lock

KVM maintains a global mmio valid generation-number which is stored in
kvm->memslots.generation and every mmio spte stores the current global
generation-number into his available bits when it is created

When KVM need zap all mmio sptes, it just simply increase the global
generation-number. When guests do mmio access, KVM intercepts a MMIO #PF
then it walks the shadow page table and get the mmio spte. If the
generation-number on the spte does not equal the global generation-number,
it will go to the normal #PF handler to update the mmio spte

Since 19 bits are used to store generation-number on mmio spte, we zap all
mmio sptes when the number is round
Signed-off-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Reviewed-by: NGleb Natapov <gleb@redhat.com>
Reviewed-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Define some meaningful names instead of raw code
Signed-off-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Reviewed-by: NGleb Natapov <gleb@redhat.com>
Reviewed-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Store the generation-number into bit3 ~ bit11 and bit52 ~ bit61, totally
19 bits can be used, it should be enough for nearly all most common cases

In this patch, the generation-number is always 0, it will be changed in
the later patch

[Gleb: masking generation bits from spte in get_mmio_spte_gfn() and
       get_mmio_spte_access()]
Signed-off-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Reviewed-by: NGleb Natapov <gleb@redhat.com>
Reviewed-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Quote Gleb's mail:
| why don't we check for sp->role.invalid in
| kvm_mmu_prepare_zap_page before calling kvm_reload_remote_mmus()?

and

| Actually we can add check for is_obsolete_sp() there too since
| kvm_mmu_invalidate_all_pages() already calls kvm_reload_remote_mmus()
| after incrementing mmu_valid_gen.

[ Xiao: add some comments and the check of is_obsolete_sp() ]
Signed-off-by: NGleb Natapov <gleb@redhat.com>
Signed-off-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Reviewed-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>

As Marcelo pointed out that
| "(retention of large number of pages while zapping)
| can be fatal, it can lead to OOM and host crash"

We introduce a list, kvm->arch.zapped_obsolete_pages, to link all
the pages which are deleted from the mmu cache but not actually
freed. When page reclaiming is needed, we always zap this kind of
pages first.
Signed-off-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Reviewed-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>

kvm_zap_obsolete_pages uses lock-break technique to zap pages,
it will flush tlb every time when it does lock-break

We can reload mmu on all vcpus after updating the generation
number so that the obsolete pages are not used on any vcpus,
after that we do not need to flush tlb when obsolete pages
are zapped

It will do kvm_mmu_prepare_zap_page many times and use one
kvm_mmu_commit_zap_page to collapse tlb flush, the side-effects
is that causes obsolete pages unlinked from active_list but leave
on hash-list, so we add the comment around the hash list walker

Note: kvm_mmu_commit_zap_page is still needed before free
the pages since other vcpus may be doing locklessly shadow
page walking
Signed-off-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Reviewed-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>

Zap at lease 10 pages before releasing mmu-lock to reduce the overload
caused by requiring lock

After the patch, kvm_zap_obsolete_pages can forward progress anyway,
so update the comments

[ It improves the case 0.6% ~ 1% that do kernel building meanwhile read
  PCI ROM. ]

Note: i am not sure that "10" is the best speculative value, i just
guessed that '10' can make vcpu do not spend long time on
kvm_zap_obsolete_pages and do not cause mmu-lock too hungry.
Signed-off-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Reviewed-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>

The obsolete page will be zapped soon, do not reuse it to
reduce future page fault
Signed-off-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Reviewed-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>

It is good for debug and development
Signed-off-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Reviewed-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>

Replace kvm_mmu_zap_all by kvm_mmu_invalidate_zap_all_pages
Signed-off-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Reviewed-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>

The current kvm_mmu_zap_all is really slow - it is holding mmu-lock to
walk and zap all shadow pages one by one, also it need to zap all guest
page's rmap and all shadow page's parent spte list. Particularly, things
become worse if guest uses more memory or vcpus. It is not good for
scalability

In this patch, we introduce a faster way to invalidate all shadow pages.
KVM maintains a global mmu invalid generation-number which is stored in
kvm->arch.mmu_valid_gen and every shadow page stores the current global
generation-number into sp->mmu_valid_gen when it is created

When KVM need zap all shadow pages sptes, it just simply increase the
global generation-number then reload root shadow pages on all vcpus.
Vcpu will create a new shadow page table according to current kvm's
generation-number. It ensures the old pages are not used any more.
Then the obsolete pages (sp->mmu_valid_gen != kvm->arch.mmu_valid_gen)
are zapped by using lock-break technique
Signed-off-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Reviewed-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>

Do locking around each case separately instead of having one lock and two
unlocks. Move root_hpa assignment out of the lock.
Signed-off-by: NGleb Natapov <gleb@redhat.com>

No need to open-code this function.
Signed-off-by: NTakuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Reviewed-by: NXiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>

With the following commit, shadow pages can be zapped at random during
a shadow page talbe walk:
  KVM: MMU: Move kvm_mmu_free_some_pages() into kvm_mmu_alloc_page()
  7ddca7e4

This patch reverts it and fixes __direct_map() and FNAME(fetch)().
Signed-off-by: NTakuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: NGleb Natapov <gleb@redhat.com>

The current name "kvm_mmu_free_some_pages" should be used for something
that actually frees some shadow pages, as we expect from the name, but
what the function is doing is to make some, KVM_MIN_FREE_MMU_PAGES,
shadow pages available: it does nothing when there are enough.

This patch changes the name to reflect this meaning better; while doing
this renaming, the code in the wrapper function is inlined into the main
body since the whole function will be inlined into the only caller now.
Signed-off-by: NTakuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>

What this function is doing is to ensure that the number of shadow pages
does not exceed the maximum limit stored in n_max_mmu_pages: so this is
placed at every code path that can reach kvm_mmu_alloc_page().

Although it might have some sense to spread this function in each such
code path when it could be called before taking mmu_lock, the rule was
changed not to do so.

Taking this background into account, this patch moves it into
kvm_mmu_alloc_page() and simplifies the code.

Note: the unlikely hint in kvm_mmu_free_some_pages() guarantees that the
overhead of this function is almost zero except when we actually need to
allocate some shadow pages, so we do not need to care about calling it
multiple times in one path by doing kvm_mmu_get_page() a few times.
Signed-off-by: NTakuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>

When we create or move a memory slot, we need to zap mmio sptes.
Currently, zap_all() is used for this and this is causing two problems:
 - extra page faults after zapping mmu pages
 - long mmu_lock hold time during zapping mmu pages

For the latter, Marcelo reported a disastrous mmu_lock hold time during
hot-plug, which made the guest unresponsive for a long time.

This patch takes a simple way to fix these problems: do not zap mmu
pages unless they are marked mmio cached.  On our test box, this took
only 50us for the 4GB guest and we did not see ms of mmu_lock hold time
any more.

Note that we still need to do zap_all() for other cases.  So another
work is also needed: Xiao's work may be the one.
Reviewed-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NTakuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: NGleb Natapov <gleb@redhat.com>

This will be used not to zap unrelated mmu pages when creating/moving
a memory slot later.
Reviewed-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NTakuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: NGleb Natapov <gleb@redhat.com>

Make the code for zapping the oldest mmu page, placed at the tail of the
active list, a separate function.
Reviewed-by: NGleb Natapov <gleb@redhat.com>
Signed-off-by: NTakuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>

We are traversing the linked list, invalid_list, deleting each entry by
kvm_mmu_free_page().  _safe version is there for such a case.
Reviewed-by: NGleb Natapov <gleb@redhat.com>
Signed-off-by: NTakuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>