diff mbox series

[24/24] kvm: x86/mmu: Allow parallel page faults for the TDP MMU

Message ID 20210112181041.356734-25-bgardon@google.com (mailing list archive)
State New, archived
Headers show
Series Allow parallel page faults with TDP MMU | expand

Commit Message

Ben Gardon Jan. 12, 2021, 6:10 p.m. UTC 
Make the last few changes necessary to enable the TDP MMU to handle page
faults in parallel while holding the mmu_lock in read mode.

Reviewed-by: Peter Feiner <pfeiner@google.com>

Signed-off-by: Ben Gardon <bgardon@google.com>
---
 arch/x86/kvm/mmu/mmu.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

Comments

Sean Christopherson Jan. 21, 2021, 12:55 a.m. UTC | #1 
On Tue, Jan 12, 2021, Ben Gardon wrote:
> Make the last few changes necessary to enable the TDP MMU to handle page
> faults in parallel while holding the mmu_lock in read mode.
> 
> Reviewed-by: Peter Feiner <pfeiner@google.com>
> 
> Signed-off-by: Ben Gardon <bgardon@google.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 280d7cd6f94b..fa111ceb67d4 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -3724,7 +3724,12 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
>  		return r;
>  
>  	r = RET_PF_RETRY;
> -	kvm_mmu_lock(vcpu->kvm);
> +
> +	if (is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa))

Off topic, what do you think about rewriting is_tdp_mmu_root() to be both more
performant and self-documenting as to when is_tdp_mmu_root() !=
kvm->arch.tdp_mmu_enabled?  E.g. key off is_guest_mode() and then do a thorough
audit/check when CONFIG_KVM_MMU_AUDIT=y?

#ifdef CONFIG_KVM_MMU_AUDIT
bool is_tdp_mmu_root(struct kvm *kvm, hpa_t hpa)
{
	struct kvm_mmu_page *sp;

	if (!kvm->arch.tdp_mmu_enabled)
		return false;
	if (WARN_ON(!VALID_PAGE(hpa)))
		return false;

	sp = to_shadow_page(hpa);
	if (WARN_ON(!sp))
		return false;

	return sp->tdp_mmu_page && sp->root_count;
}
#endif

bool is_tdp_mmu(struct kvm_vcpu *vcpu)
{
	bool is_tdp_mmu = kvm->arch.tdp_mmu_enabled && !is_guest_mode(vcpu);

#ifdef CONFIG_KVM_MMU_AUDIT
	WARN_ON(is_tdp_mmu != is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa));
#endif
	return is_tdp_mmu;
}

> +		kvm_mmu_lock_shared(vcpu->kvm);
> +	else
> +		kvm_mmu_lock(vcpu->kvm);
> +
>  	if (mmu_notifier_retry(vcpu->kvm, mmu_seq))
>  		goto out_unlock;
>  	r = make_mmu_pages_available(vcpu);
> @@ -3739,7 +3744,10 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
>  				 prefault, is_tdp);
>  
>  out_unlock:
> -	kvm_mmu_unlock(vcpu->kvm);
> +	if (is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa))
> +		kvm_mmu_unlock_shared(vcpu->kvm);
> +	else
> +		kvm_mmu_unlock(vcpu->kvm);
>  	kvm_release_pfn_clean(pfn);
>  	return r;
>  }
> -- 
> 2.30.0.284.gd98b1dd5eaa7-goog
>
Paolo Bonzini Jan. 26, 2021, 1:37 p.m. UTC | #2 
On 12/01/21 19:10, Ben Gardon wrote:
> +	if (is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa))
> +		kvm_mmu_lock_shared(vcpu->kvm);
> +	else
> +		kvm_mmu_lock(vcpu->kvm);

Perhaps the better API would be kvm_mmu_lock/unlock_root; not exposing 
kvm_mmu_lock/unlock_shared and kvm_mmu_lock/unlock_exclusive at all, 
just like you use rwlock_needbreak directly in kvm_mmu_lock_needbreak.

Paolo
Ben Gardon Jan. 26, 2021, 9:57 p.m. UTC | #3 
On Wed, Jan 20, 2021 at 4:56 PM Sean Christopherson <seanjc@google.com> wrote:
>
> On Tue, Jan 12, 2021, Ben Gardon wrote:
> > Make the last few changes necessary to enable the TDP MMU to handle page
> > faults in parallel while holding the mmu_lock in read mode.
> >
> > Reviewed-by: Peter Feiner <pfeiner@google.com>
> >
> > Signed-off-by: Ben Gardon <bgardon@google.com>
> > ---
> >  arch/x86/kvm/mmu/mmu.c | 12 ++++++++++--
> >  1 file changed, 10 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 280d7cd6f94b..fa111ceb67d4 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -3724,7 +3724,12 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
> >               return r;
> >
> >       r = RET_PF_RETRY;
> > -     kvm_mmu_lock(vcpu->kvm);
> > +
> > +     if (is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa))
>
> Off topic, what do you think about rewriting is_tdp_mmu_root() to be both more
> performant and self-documenting as to when is_tdp_mmu_root() !=
> kvm->arch.tdp_mmu_enabled?  E.g. key off is_guest_mode() and then do a thorough
> audit/check when CONFIG_KVM_MMU_AUDIT=y?
>
> #ifdef CONFIG_KVM_MMU_AUDIT
> bool is_tdp_mmu_root(struct kvm *kvm, hpa_t hpa)
> {
>         struct kvm_mmu_page *sp;
>
>         if (!kvm->arch.tdp_mmu_enabled)
>                 return false;
>         if (WARN_ON(!VALID_PAGE(hpa)))
>                 return false;
>
>         sp = to_shadow_page(hpa);
>         if (WARN_ON(!sp))
>                 return false;
>
>         return sp->tdp_mmu_page && sp->root_count;
> }
> #endif
>
> bool is_tdp_mmu(struct kvm_vcpu *vcpu)
> {
>         bool is_tdp_mmu = kvm->arch.tdp_mmu_enabled && !is_guest_mode(vcpu);
>
> #ifdef CONFIG_KVM_MMU_AUDIT
>         WARN_ON(is_tdp_mmu != is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa));
> #endif
>         return is_tdp_mmu;
> }

Great suggestions. In the interest of keeping this (already enormous)
series small, I'm inclined to make those changes in a future series if
that's alright with you.

>
> > +             kvm_mmu_lock_shared(vcpu->kvm);
> > +     else
> > +             kvm_mmu_lock(vcpu->kvm);
> > +
> >       if (mmu_notifier_retry(vcpu->kvm, mmu_seq))
> >               goto out_unlock;
> >       r = make_mmu_pages_available(vcpu);
> > @@ -3739,7 +3744,10 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
> >                                prefault, is_tdp);
> >
> >  out_unlock:
> > -     kvm_mmu_unlock(vcpu->kvm);
> > +     if (is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa))
> > +             kvm_mmu_unlock_shared(vcpu->kvm);
> > +     else
> > +             kvm_mmu_unlock(vcpu->kvm);
> >       kvm_release_pfn_clean(pfn);
> >       return r;
> >  }
> > --
> > 2.30.0.284.gd98b1dd5eaa7-goog
> >
Sean Christopherson Jan. 27, 2021, 5:14 p.m. UTC | #4 
On Tue, Jan 26, 2021, Ben Gardon wrote:
> On Wed, Jan 20, 2021 at 4:56 PM Sean Christopherson <seanjc@google.com> wrote:
> >
> > On Tue, Jan 12, 2021, Ben Gardon wrote:
> > > Make the last few changes necessary to enable the TDP MMU to handle page
> > > faults in parallel while holding the mmu_lock in read mode.
> > >
> > > Reviewed-by: Peter Feiner <pfeiner@google.com>
> > >
> > > Signed-off-by: Ben Gardon <bgardon@google.com>
> > > ---
> > >  arch/x86/kvm/mmu/mmu.c | 12 ++++++++++--
> > >  1 file changed, 10 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > > index 280d7cd6f94b..fa111ceb67d4 100644
> > > --- a/arch/x86/kvm/mmu/mmu.c
> > > +++ b/arch/x86/kvm/mmu/mmu.c
> > > @@ -3724,7 +3724,12 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
> > >               return r;
> > >
> > >       r = RET_PF_RETRY;
> > > -     kvm_mmu_lock(vcpu->kvm);
> > > +
> > > +     if (is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa))
> >
> > Off topic, what do you think about rewriting is_tdp_mmu_root() to be both more
> > performant and self-documenting as to when is_tdp_mmu_root() !=
> > kvm->arch.tdp_mmu_enabled?  E.g. key off is_guest_mode() and then do a thorough
> > audit/check when CONFIG_KVM_MMU_AUDIT=y?
> >
> > #ifdef CONFIG_KVM_MMU_AUDIT
> > bool is_tdp_mmu_root(struct kvm *kvm, hpa_t hpa)
> > {
> >         struct kvm_mmu_page *sp;
> >
> >         if (!kvm->arch.tdp_mmu_enabled)
> >                 return false;
> >         if (WARN_ON(!VALID_PAGE(hpa)))
> >                 return false;
> >
> >         sp = to_shadow_page(hpa);
> >         if (WARN_ON(!sp))
> >                 return false;
> >
> >         return sp->tdp_mmu_page && sp->root_count;
> > }
> > #endif
> >
> > bool is_tdp_mmu(struct kvm_vcpu *vcpu)
> > {
> >         bool is_tdp_mmu = kvm->arch.tdp_mmu_enabled && !is_guest_mode(vcpu);
> >
> > #ifdef CONFIG_KVM_MMU_AUDIT
> >         WARN_ON(is_tdp_mmu != is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa));
> > #endif
> >         return is_tdp_mmu;
> > }
> 
> Great suggestions. In the interest of keeping this (already enormous)
> series small, I'm inclined to make those changes in a future series if
> that's alright with you.

Yep, definitely a different series.
diff mbox series

Patch

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 280d7cd6f94b..fa111ceb67d4 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3724,7 +3724,12 @@  static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
 		return r;
 
 	r = RET_PF_RETRY;
-	kvm_mmu_lock(vcpu->kvm);
+
+	if (is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa))
+		kvm_mmu_lock_shared(vcpu->kvm);
+	else
+		kvm_mmu_lock(vcpu->kvm);
+
 	if (mmu_notifier_retry(vcpu->kvm, mmu_seq))
 		goto out_unlock;
 	r = make_mmu_pages_available(vcpu);
@@ -3739,7 +3744,10 @@  static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
 				 prefault, is_tdp);
 
 out_unlock:
-	kvm_mmu_unlock(vcpu->kvm);
+	if (is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa))
+		kvm_mmu_unlock_shared(vcpu->kvm);
+	else
+		kvm_mmu_unlock(vcpu->kvm);
 	kvm_release_pfn_clean(pfn);
 	return r;
 }