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

Marcelo Tosatti
2011-06-20T16:16:32Z

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@cn.fujitsu.com>
> > ---
> > 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.