Re: [PATCH 04/15] KVM: MMU: cache mmio info on page fault path

[Marcelo Tosatti]

On Mon, Jun 20, 2011 at 01:14:32PM -0300, Marcelo Tosatti wrote:
> On Tue, Jun 07, 2011 at 09:00:30PM +0800, Xiao Guangrong wrote:
> > If the page fault is caused by mmio, we can cache the mmio info, later, we do
> > not need to walk guest page table and quickly know it is a mmio fault while we
> > emulate the mmio instruction
> > 
> > Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxx>
> > ---
> >  arch/x86/include/asm/kvm_host.h |    5 +++
> >  arch/x86/kvm/mmu.c              |   21 +++++----------
> >  arch/x86/kvm/mmu.h              |   23 +++++++++++++++++
> >  arch/x86/kvm/paging_tmpl.h      |   21 ++++++++++-----
> >  arch/x86/kvm/x86.c              |   52 ++++++++++++++++++++++++++++++--------
> >  arch/x86/kvm/x86.h              |   36 +++++++++++++++++++++++++++
> >  6 files changed, 126 insertions(+), 32 deletions(-)
> > 
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index d167039..326af42 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -414,6 +414,11 @@ struct kvm_vcpu_arch {
> >  	u64 mcg_ctl;
> >  	u64 *mce_banks;
> >  
> > +	/* Cache MMIO info */
> > +	u64 mmio_gva;
> > +	unsigned access;
> > +	gfn_t mmio_gfn;
> > +
> >  	/* used for guest single stepping over the given code position */
> >  	unsigned long singlestep_rip;
> >  
> 
> Why you're not implementing the original idea to cache the MMIO
> attribute of an address into the spte?
> 
> That solution is wider reaching than a one-entry cache, and was proposed
> to overcome large number of memslots.
> 
> If the access pattern switches between different addresses this one
> solution is doomed.

Nevermind, its later in the series.

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