2022-08-24 09:45:40

by Hou Wenlong

Subject: [PATCH v2 6/6] KVM: x86/mmu: Use 1 as the size of gfn range for tlb flushing in FNAME(invlpg)()

Only SP with PG_LEVLE_4K level could be unsync, so the size of gfn range
must be 1.

Signed-off-by: Hou Wenlong <[email protected]>
---
arch/x86/kvm/mmu/paging_tmpl.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 04149c704d5b..486a3163b1e4 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -937,7 +937,8 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva, hpa_t root_hpa)

mmu_page_zap_pte(vcpu->kvm, sp, sptep, NULL);
if (is_shadow_present_pte(old_spte))
- kvm_flush_remote_tlbs_sptep(vcpu->kvm, sptep);
+ kvm_flush_remote_tlbs_gfn(vcpu->kvm,
+ kvm_mmu_page_get_gfn(sp, sptep - sp->spt), 1);

if (!rmap_can_add(vcpu))
break;
--
2.31.1

2022-09-07 18:27:33

by David Matlack

Subject: Re: [PATCH v2 6/6] KVM: x86/mmu: Use 1 as the size of gfn range for tlb flushing in FNAME(invlpg)()

On Wed, Aug 24, 2022 at 05:29:23PM +0800, Hou Wenlong wrote:
> Only SP with PG_LEVLE_4K level could be unsync, so the size of gfn range
> must be 1.
>
> Signed-off-by: Hou Wenlong <[email protected]>
> ---
> arch/x86/kvm/mmu/paging_tmpl.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
> index 04149c704d5b..486a3163b1e4 100644
> --- a/arch/x86/kvm/mmu/paging_tmpl.h
> +++ b/arch/x86/kvm/mmu/paging_tmpl.h
> @@ -937,7 +937,8 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva, hpa_t root_hpa)
>
> mmu_page_zap_pte(vcpu->kvm, sp, sptep, NULL);
> if (is_shadow_present_pte(old_spte))
> - kvm_flush_remote_tlbs_sptep(vcpu->kvm, sptep);
> + kvm_flush_remote_tlbs_gfn(vcpu->kvm,
> + kvm_mmu_page_get_gfn(sp, sptep - sp->spt), 1);

The third argument to kvm_flush_remote_tlbs_gfn() is the level, not the
number of pages. But that aside, I don't understand why this patch is
necessary. kvm_flush_remote_tlbs_sptep() should already do the right
thing.

>
> if (!rmap_can_add(vcpu))
> break;
> --
> 2.31.1
>

2022-09-13 13:32:16

by Hou Wenlong

Subject: Re: [PATCH v2 6/6] KVM: x86/mmu: Use 1 as the size of gfn range for tlb flushing in FNAME(invlpg)()

On Thu, Sep 08, 2022 at 01:40:16AM +0800, David Matlack wrote:
> On Wed, Aug 24, 2022 at 05:29:23PM +0800, Hou Wenlong wrote:
> > Only SP with PG_LEVLE_4K level could be unsync, so the size of gfn range
> > must be 1.
> >
> > Signed-off-by: Hou Wenlong <[email protected]>
> > ---
> > arch/x86/kvm/mmu/paging_tmpl.h | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
> > index 04149c704d5b..486a3163b1e4 100644
> > --- a/arch/x86/kvm/mmu/paging_tmpl.h
> > +++ b/arch/x86/kvm/mmu/paging_tmpl.h
> > @@ -937,7 +937,8 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva, hpa_t root_hpa)
> >
> > mmu_page_zap_pte(vcpu->kvm, sp, sptep, NULL);
> > if (is_shadow_present_pte(old_spte))
> > - kvm_flush_remote_tlbs_sptep(vcpu->kvm, sptep);
> > + kvm_flush_remote_tlbs_gfn(vcpu->kvm,
> > + kvm_mmu_page_get_gfn(sp, sptep - sp->spt), 1);
>
> The third argument to kvm_flush_remote_tlbs_gfn() is the level, not the
> number of pages. But that aside, I don't understand why this patch is
> necessary. kvm_flush_remote_tlbs_sptep() should already do the right
> thing.
>
Since only SP with PG_LEVEL_4K level could be unsync, so the level must
be PG_LEVEL_4K, then sp->role.level access could be dropped. However,
I'm not sure whether it is useful. I can drop it if it is useless.

> >
> > if (!rmap_can_add(vcpu))
> > break;
> > --
> > 2.31.1
> >

2022-09-13 15:42:09

by David Matlack

Subject: Re: [PATCH v2 6/6] KVM: x86/mmu: Use 1 as the size of gfn range for tlb flushing in FNAME(invlpg)()

On Tue, Sep 13, 2022 at 5:58 AM Hou Wenlong <[email protected]> wrote:
>
> On Thu, Sep 08, 2022 at 01:40:16AM +0800, David Matlack wrote:
> > On Wed, Aug 24, 2022 at 05:29:23PM +0800, Hou Wenlong wrote:
> > > Only SP with PG_LEVLE_4K level could be unsync, so the size of gfn range
> > > must be 1.
> > >
> > > Signed-off-by: Hou Wenlong <[email protected]>
> > > ---
> > > arch/x86/kvm/mmu/paging_tmpl.h | 3 ++-
> > > 1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
> > > index 04149c704d5b..486a3163b1e4 100644
> > > --- a/arch/x86/kvm/mmu/paging_tmpl.h
> > > +++ b/arch/x86/kvm/mmu/paging_tmpl.h
> > > @@ -937,7 +937,8 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva, hpa_t root_hpa)
> > >
> > > mmu_page_zap_pte(vcpu->kvm, sp, sptep, NULL);
> > > if (is_shadow_present_pte(old_spte))
> > > - kvm_flush_remote_tlbs_sptep(vcpu->kvm, sptep);
> > > + kvm_flush_remote_tlbs_gfn(vcpu->kvm,
> > > + kvm_mmu_page_get_gfn(sp, sptep - sp->spt), 1);
> >
> > The third argument to kvm_flush_remote_tlbs_gfn() is the level, not the
> > number of pages. But that aside, I don't understand why this patch is
> > necessary. kvm_flush_remote_tlbs_sptep() should already do the right
> > thing.
> >
> Since only SP with PG_LEVEL_4K level could be unsync, so the level must
> be PG_LEVEL_4K, then sp->role.level access could be dropped. However,
> I'm not sure whether it is useful. I can drop it if it is useless.

Ah, I see. I would be surprised if avoiding the read of sp->role.level
has any noticeable impact on VM performance so I vote to drop this patch.


>
> > >
> > > if (!rmap_can_add(vcpu))
> > > break;
> > > --
> > > 2.31.1
> > >

2022-09-16 20:12:18

by Sean Christopherson

Subject: Re: [PATCH v2 6/6] KVM: x86/mmu: Use 1 as the size of gfn range for tlb flushing in FNAME(invlpg)()

On Tue, Sep 13, 2022, David Matlack wrote:
> On Tue, Sep 13, 2022 at 5:58 AM Hou Wenlong <[email protected]> wrote:
> >
> > On Thu, Sep 08, 2022 at 01:40:16AM +0800, David Matlack wrote:
> > > On Wed, Aug 24, 2022 at 05:29:23PM +0800, Hou Wenlong wrote:
> > > > Only SP with PG_LEVLE_4K level could be unsync, so the size of gfn range
> > > > must be 1.
> > > >
> > > > Signed-off-by: Hou Wenlong <[email protected]>
> > > > ---
> > > > arch/x86/kvm/mmu/paging_tmpl.h | 3 ++-
> > > > 1 file changed, 2 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
> > > > index 04149c704d5b..486a3163b1e4 100644
> > > > --- a/arch/x86/kvm/mmu/paging_tmpl.h
> > > > +++ b/arch/x86/kvm/mmu/paging_tmpl.h
> > > > @@ -937,7 +937,8 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva, hpa_t root_hpa)
> > > >
> > > > mmu_page_zap_pte(vcpu->kvm, sp, sptep, NULL);
> > > > if (is_shadow_present_pte(old_spte))
> > > > - kvm_flush_remote_tlbs_sptep(vcpu->kvm, sptep);
> > > > + kvm_flush_remote_tlbs_gfn(vcpu->kvm,
> > > > + kvm_mmu_page_get_gfn(sp, sptep - sp->spt), 1);
> > >
> > > The third argument to kvm_flush_remote_tlbs_gfn() is the level, not the
> > > number of pages. But that aside, I don't understand why this patch is
> > > necessary. kvm_flush_remote_tlbs_sptep() should already do the right
> > > thing.
> > >
> > Since only SP with PG_LEVEL_4K level could be unsync, so the level must
> > be PG_LEVEL_4K, then sp->role.level access could be dropped. However,
> > I'm not sure whether it is useful. I can drop it if it is useless.
>
> Ah, I see. I would be surprised if avoiding the read of sp->role.level
> has any noticeable impact on VM performance so I vote to drop this patch.

Agreed, the cost of the sp->role.level lookup is negligible in this case, and IMO
using kvm_flush_remote_tlbs_sptep() is more intuitive.

If kvm_flush_remote_tlbs_sptep() didn't exist and this was open coding the use of
kvm_flush_remote_tlbs_with_address() + KVM_PAGES_PER_HPAGE(), then I would be in
favor of hardcoding '1', because at that point the use of KVM_PAGES_PER_HPAGE() is
misleading in its own way.