Re: [PATCH 1/4] KVM: MMU: don't drop spte if overwrite it from W to RO
On 11/17/2010 04:24 AM, Marcelo Tosatti wrote: > On Fri, Nov 12, 2010 at 06:30:22PM +0800, Xiao Guangrong wrote: >> We just need flush tlb if overwrite a writable spte with a read-only one >> >> Signed-off-by: Xiao Guangrong >> --- >> arch/x86/kvm/mmu.c | 19 +-- >> 1 files changed, 9 insertions(+), 10 deletions(-) >> >> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c >> index 4b6d54c..1a93ab4 100644 >> --- a/arch/x86/kvm/mmu.c >> +++ b/arch/x86/kvm/mmu.c >> @@ -2044,6 +2044,15 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep, >> if (pte_access & ACC_WRITE_MASK) >> mark_page_dirty(vcpu->kvm, gfn); >> >> +/* >> + * If we overwrite a writable spte with a read-only one, >> + * flush remote TLBs. Otherwise rmap_write_protect will >> + * find a read-only spte, even though the writable spte >> + * might be cached on a CPU's TLB. >> + */ >> +else if (is_writable_pte(*sptep)) >> +ret = 1; >> + > > The return value of set_spte indicates whether the gfn being mapped to > was write protected, not if a TLB flush is necessary. > Yes, i also noticed this and have fixed in the v2 queue, thanks Marcelo! -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 1/4] KVM: MMU: don't drop spte if overwrite it from W to RO
On Fri, Nov 12, 2010 at 06:30:22PM +0800, Xiao Guangrong wrote:
> We just need flush tlb if overwrite a writable spte with a read-only one
>
> Signed-off-by: Xiao Guangrong
> ---
> arch/x86/kvm/mmu.c | 19 +--
> 1 files changed, 9 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 4b6d54c..1a93ab4 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -2044,6 +2044,15 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
> if (pte_access & ACC_WRITE_MASK)
> mark_page_dirty(vcpu->kvm, gfn);
>
> + /*
> + * If we overwrite a writable spte with a read-only one,
> + * flush remote TLBs. Otherwise rmap_write_protect will
> + * find a read-only spte, even though the writable spte
> + * might be cached on a CPU's TLB.
> + */
> + else if (is_writable_pte(*sptep))
> + ret = 1;
> +
The return value of set_spte indicates whether the gfn being mapped to
was write protected, not if a TLB flush is necessary.
> set_pte:
> update_spte(sptep, spte);
> done:
> @@ -2084,16 +2093,6 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64
> *sptep,
>spte_to_pfn(*sptep), pfn);
> drop_spte(vcpu->kvm, sptep, shadow_trap_nonpresent_pte);
> kvm_flush_remote_tlbs(vcpu->kvm);
> - /*
> - * If we overwrite a writable spte with a read-only one,
> - * drop it and flush remote TLBs. Otherwise rmap_write_protect
> - * will find a read-only spte, even though the writable spte
> - * might be cached on a CPU's TLB.
> - */
> - } else if (is_writable_pte(*sptep) &&
> - (!(pte_access & ACC_WRITE_MASK) || !dirty)) {
> - drop_spte(vcpu->kvm, sptep, shadow_trap_nonpresent_pte);
> - kvm_flush_remote_tlbs(vcpu->kvm);
> } else
> was_rmapped = 1;
And here, flush will only happen if overwrite is RW->RO.
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 1/4] KVM: MMU: don't drop spte if overwrite it from W to RO
On 11/14/2010 06:52 PM, Avi Kivity wrote: > On 11/12/2010 12:30 PM, Xiao Guangrong wrote: >> We just need flush tlb if overwrite a writable spte with a read-only one >> > > What are the advantages? Avoid playing with rmap, and avoid a window > where the spte is missing? > Both, but only the first was in my mind when i'm making the patch :-) -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 1/4] KVM: MMU: don't drop spte if overwrite it from W to RO
On 11/12/2010 12:30 PM, Xiao Guangrong wrote: We just need flush tlb if overwrite a writable spte with a read-only one What are the advantages? Avoid playing with rmap, and avoid a window where the spte is missing? (they are worth the patch, just seeing if I'm not missing something) -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[PATCH 1/4] KVM: MMU: don't drop spte if overwrite it from W to RO
We just need flush tlb if overwrite a writable spte with a read-only one
Signed-off-by: Xiao Guangrong
---
arch/x86/kvm/mmu.c | 19 +--
1 files changed, 9 insertions(+), 10 deletions(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 4b6d54c..1a93ab4 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2044,6 +2044,15 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
if (pte_access & ACC_WRITE_MASK)
mark_page_dirty(vcpu->kvm, gfn);
+ /*
+* If we overwrite a writable spte with a read-only one,
+* flush remote TLBs. Otherwise rmap_write_protect will
+* find a read-only spte, even though the writable spte
+* might be cached on a CPU's TLB.
+*/
+ else if (is_writable_pte(*sptep))
+ ret = 1;
+
set_pte:
update_spte(sptep, spte);
done:
@@ -2084,16 +2093,6 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64
*sptep,
spte_to_pfn(*sptep), pfn);
drop_spte(vcpu->kvm, sptep, shadow_trap_nonpresent_pte);
kvm_flush_remote_tlbs(vcpu->kvm);
- /*
-* If we overwrite a writable spte with a read-only one,
-* drop it and flush remote TLBs. Otherwise rmap_write_protect
-* will find a read-only spte, even though the writable spte
-* might be cached on a CPU's TLB.
-*/
- } else if (is_writable_pte(*sptep) &&
- (!(pte_access & ACC_WRITE_MASK) || !dirty)) {
- drop_spte(vcpu->kvm, sptep, shadow_trap_nonpresent_pte);
- kvm_flush_remote_tlbs(vcpu->kvm);
} else
was_rmapped = 1;
}
--
1.7.0.4
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
