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

Marcelo Tosatti
2011-06-20T16:14:51Z

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.