lkml.org 
[lkml]   [2013]   [Jun]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v3 0/6] KVM: MMU: fast invalidate all mmio sptes
On Mon, Jun 17, 2013 at 07:59:15PM +0800, Xiao Guangrong wrote:
> Sorry for the delay reply since i was on vacation.
>
> On 06/15/2013 10:22 AM, Takuya Yoshikawa wrote:
> > On Thu, 13 Jun 2013 21:08:21 -0300
> > Marcelo Tosatti <mtosatti@redhat.com> wrote:
> >
> >> On Fri, Jun 07, 2013 at 04:51:22PM +0800, Xiao Guangrong wrote:
> >
> >> - Where is the generation number increased?
> >
> > Looks like when a new slot is installed in update_memslots() because
> > it's based on slots->generation. This is not restricted to "create"
> > and "move".
>
> Yes. It reuses slots->generation to avoid unnecessary synchronizations
> (RCU, memory barrier).
>
> Increasing mmio generation number in the case of "create" and "move"
> is ok - it is no addition work unless mmio generation number is overflow
> which is hardly triggered (since the valid mmio generation number is
> large enough and zap_all is scale well now.) and the mmio spte is updated
> only when it is used in the future.
>
> >
> >> - Should use spinlock breakable code in kvm_mmu_zap_mmio_sptes()
> >> (picture guest with 512GB of RAM, even walking all those pages is
> >> expensive) (ah, patch to remove kvm_mmu_zap_mmio_sptes does that).
> >> - Is -13 enough to test wraparound? Its highly likely the guest has
> >> not began executing by the time 13 kvm_set_memory_calls are made
> >> (so no sptes around). Perhaps -2000 is more sensible (should confirm
> >> though).
> >
> > In the future, after we've tested enough, we should change the testing
> > code to be executed only for some debugging configs. Especially, if we
> > change zap_mmio_sptes() to zap_all_shadows(), very common guests, even
> > without huge memory like 512GB, can see the effect induced by sudden page
> > faults unnecessarily.
> >
> > If necessary, developers can test the wraparound code by lowering the
> > max_gen itself anyway.
>
> I agree.
>
> >
> >> - Why remove "if (change == KVM_MR_CREATE) || (change
> >> == KVM_MR_MOVE)" from kvm_arch_commit_memory_region?
> >> Its instructive.
> >
> > There may be a chance that we miss generation wraparounds if we don't
> > check other cases: seems unlikely, but theoretically possible.
> >
> > In short, all memory slot changes make mmio sptes stored in shadow pages
> > obsolete, or zapped for wraparounds, in the new way -- am I right?
>
> Yes. You are definitely right. :)
>
> Takuya-san, thank you very much for you answering the questions for me and thanks
> all of you for patiently reviewing my patches.
>
> Marcelo, your points?

Agreed - points are clear. Patchset looks good.



\
 
 \ /
  Last update: 2013-06-19 00:41    [W:0.428 / U:0.072 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site