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  1. 15 1月, 2010 1 次提交
    • M
      vhost_net: a kernel-level virtio server · 3a4d5c94
      由 Michael S. Tsirkin 提交于 
      What it is: vhost net is a character device that can be used to reduce
the number of system calls involved in virtio networking.
Existing virtio net code is used in the guest without modification.

There's similarity with vringfd, with some differences and reduced scope
- uses eventfd for signalling
- structures can be moved around in memory at any time (good for
  migration, bug work-arounds in userspace)
- write logging is supported (good for migration)
- support memory table and not just an offset (needed for kvm)

common virtio related code has been put in a separate file vhost.c and
can be made into a separate module if/when more backends appear.  I used
Rusty's lguest.c as the source for developing this part : this supplied
me with witty comments I wouldn't be able to write myself.

What it is not: vhost net is not a bus, and not a generic new system
call. No assumptions are made on how guest performs hypercalls.
Userspace hypervisors are supported as well as kvm.

How it works: Basically, we connect virtio frontend (configured by
userspace) to a backend. The backend could be a network device, or a tap
device.  Backend is also configured by userspace, including vlan/mac
etc.

Status: This works for me, and I haven't see any crashes.
Compared to userspace, people reported improved latency (as I save up to
4 system calls per packet), as well as better bandwidth and CPU
utilization.

Features that I plan to look at in the future:
- mergeable buffers
- zero copy
- scalability tuning: figure out the best threading model to use

Note on RCU usage (this is also documented in vhost.h, near
private_pointer which is the value protected by this variant of RCU):
what is happening is that the rcu_dereference() is being used in a
workqueue item.  The role of rcu_read_lock() is taken on by the start of
execution of the workqueue item, of rcu_read_unlock() by the end of
execution of the workqueue item, and of synchronize_rcu() by
flush_workqueue()/flush_work(). In the future we might need to apply
some gcc attribute or sparse annotation to the function passed to
INIT_WORK(). Paul's ack below is for this RCU usage.

(Includes fixes by Alan Cox <alan@linux.intel.com>,
David L Stevens <dlstevens@us.ibm.com>,
Chris Wright <chrisw@redhat.com>)
Acked-by: NRusty Russell <rusty@rustcorp.com.au>
Acked-by: NArnd Bergmann <arnd@arndb.de>
Acked-by: N"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
      3a4d5c94
  3. 19 12月, 2009 5 次提交
  5. 16 12月, 2009 3 次提交
  7. 15 12月, 2009 6 次提交
  9. 12 12月, 2009 1 次提交
  11. 11 12月, 2009 2 次提交
  13. 07 12月, 2009 18 次提交
  15. 06 12月, 2009 1 次提交
  17. 04 12月, 2009 1 次提交
  19. 03 12月, 2009 2 次提交
    • C
      KVM: s390: Fix prefix register checking in arch/s390/kvm/sigp.c · f50146bd
      由 Carsten Otte 提交于 
      This patch corrects the checking of the new address for the prefix register.
On s390, the prefix register is used to address the cpu's lowcore (address
0...8k). This check is supposed to verify that the memory is readable and
present.
copy_from_guest is a helper function, that can be used to read from guest
memory. It applies prefixing, adds the start address of the guest memory in
user, and then calls copy_from_user. Previous code was obviously broken for
two reasons:
- prefixing should not be applied here. The current prefix register is
  going to be updated soon, and the address we're looking for will be
  0..8k after we've updated the register
- we're adding the guest origin (gmsor) twice: once in subject code
  and once in copy_from_guest

With kuli, we did not hit this problem because (a) we were lucky with
previous prefix register content, and (b) our guest memory was mmaped
very low into user address space.

Cc: stable@kernel.org
Signed-off-by: NCarsten Otte <cotte@de.ibm.com>
Reported-by: NAlexander Graf <agraf@suse.de>
Signed-off-by: NAvi Kivity <avi@redhat.com>
      f50146bd
    • C
      KVM: s390: Make psw available on all exits, not just a subset · d7b0b5eb
      由 Carsten Otte 提交于 
      This patch moves s390 processor status word into the base kvm_run
struct and keeps it up-to date on all userspace exits.

The userspace ABI is broken by this, however there are no applications
in the wild using this.  A capability check is provided so users can
verify the updated API exists.

Cc: stable@kernel.org
Signed-off-by: NCarsten Otte <cotte@de.ibm.com>
Signed-off-by: NAvi Kivity <avi@redhat.com>
      d7b0b5eb