Re: [PATCH v4 3/3] KVM: MMU: retry #PF for softmmu

Avi Kivity
2010-12-06T09:48:00Z

On 12/02/2010 11:46 AM, Xiao Guangrong wrote:
> Retry #PF for softmmu only when the current vcpu has the same cr3 as the time
> when #PF occurs
>
> Changelog:
> Just compare cr3 value since It's harmless to instantiate an spte for an
> unused translation from Marcelo's comment
>

It's not harmless. We could be in a different process, so we have to
re-fetch the gpte. Or we could have switched from one nested guest to
another.

>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index c6bb449..3f0d9a0 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -2607,9 +2607,11 @@ static int nonpaging_page_fault(struct kvm_vcpu *vcpu, gva_t gva,
> static int kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu, gva_t gva, gfn_t gfn)
> {
> struct kvm_arch_async_pf arch;
> +
> arch.token = (vcpu->arch.apf.id++<< 12) | vcpu->vcpu_id;
> arch.gfn = gfn;
> arch.direct_map = vcpu->arch.mmu.direct_map;
> + arch.cr3 = vcpu->arch.mmu.get_cr3(vcpu);
>
> return kvm_setup_async_pf(vcpu, gva, gfn,&arch);
> }
> diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
> index 23275d0..437e11a 100644
> --- a/arch/x86/kvm/paging_tmpl.h
> +++ b/arch/x86/kvm/paging_tmpl.h
> @@ -116,7 +116,7 @@ static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, pt_element_t gpte)
> */
> static int FNAME(walk_addr_generic)(struct guest_walker *walker,
> struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
> - gva_t addr, u32 access)
> + gva_t addr, u32 access, bool prefault)
> {
> pt_element_t pte;
> gfn_t table_gfn;
> @@ -194,6 +194,13 @@ walk:
> #endif
>
> if (!eperm&& !rsvd_fault&& !(pte& PT_ACCESSED_MASK)) {
> + /*
> + * Don't set gpte accessed bit if it's on
> + * speculative path.
> + */
> + if (prefault)
> + goto error;

It's actually legal to set the accessed bit on speculative access.

--
error compiling committee.c: too many arguments to function