Re: [PATCH] KVM: Defer remote tlb flushes on invlpg (v3)

[Avi Kivity <avi@redhat.com>]

Andrew Theurer wrote:
> Avi Kivity wrote:
>> KVM currently flushes the tlbs on all cpus when emulating invlpg.  This
>> is because at the time of invlpg we lose track of the page, and leaving
>> stale tlb entries could cause the guest to access the page when it is
>> later freed (say after being swapped out).
>>
>> However we have a second change to flush the tlbs, when an mmu 
>> notifier is
>> called to let us know the host pte has been invalidated.  We can safely
>> defer the flush to this point, which occurs much less frequently.  Of 
>> course,
>> we still do a local tlb flush when emulating invlpg.
>>   
> I should be able to run some performance comparisons with this in the 
> next day or two.

Excellent.  Note that while this does not improve performance relative 
to released versions of kvm; rather it undoes a performance regression 
caused by 967f61 ("KVM: Fix missing smp tlb flush in invlpg"), which 
fixes a memory corruption problem.

The workloads which will exercise this are mmu-intensive smp workloads 
with CONFIG_HIGHMEM (or CONFIG_HIGHMEM64) guests; 32-bit RHEL 3 is a 
pretty bad offender.

-- 
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