| Message ID | 1519054687-14405-1-git-send-email-shankerd@codeaurora.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Shanker, On Mon, Feb 19, 2018 at 09:38:07AM -0600, Shanker Donthineni wrote: > In AArch64/AArch32, the virtual counter uses a fixed virtual offset > of zero in the following situations as per ARMv8 specifications: > > 1) HCR_EL2.E2H is 1, and CNTVCT_EL0/CNTVCT are read from EL2. > 2) HCR_EL2.{E2H, TGE} is {1, 1}, and either: > — CNTVCT_EL0 is read from Non-secure EL0 or EL2. > — CNTVCT is read from Non-secure EL0. > > So, no need to zero CNTVOFF_EL2/CNTVOFF for VHE case. > > Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org> > --- > virt/kvm/arm/arch_timer.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c > index 70268c0..86eca324 100644 > --- a/virt/kvm/arm/arch_timer.c > +++ b/virt/kvm/arm/arch_timer.c > @@ -541,9 +541,11 @@ void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu) > * The kernel may decide to run userspace after calling vcpu_put, so > * we reset cntvoff to 0 to ensure a consistent read between user > * accesses to the virtual counter and kernel access to the physical > - * counter. > + * counter of non-VHE case. For VHE, the virtual counter uses a fixed > + * virtual offset of zero, so no need to zero CNTVOFF_EL2 register. > */ > - set_cntvoff(0); > + if (!has_vhe()) > + set_cntvoff(0); > } > > /* I'm okay with this change. I don't think there's a huge gain here though. Marc, any thoughts or concerns? Thanks, -Christoffer
On Thu, 22 Feb 2018 08:42:31 +0000, Christoffer Dall wrote: > > Hi Shanker, > > On Mon, Feb 19, 2018 at 09:38:07AM -0600, Shanker Donthineni wrote: > > In AArch64/AArch32, the virtual counter uses a fixed virtual offset > > of zero in the following situations as per ARMv8 specifications: > > > > 1) HCR_EL2.E2H is 1, and CNTVCT_EL0/CNTVCT are read from EL2. > > 2) HCR_EL2.{E2H, TGE} is {1, 1}, and either: > > ― CNTVCT_EL0 is read from Non-secure EL0 or EL2. > > ― CNTVCT is read from Non-secure EL0. > > > > So, no need to zero CNTVOFF_EL2/CNTVOFF for VHE case. > > > > Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org> > > --- > > virt/kvm/arm/arch_timer.c | 6 ++++-- > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c > > index 70268c0..86eca324 100644 > > --- a/virt/kvm/arm/arch_timer.c > > +++ b/virt/kvm/arm/arch_timer.c > > @@ -541,9 +541,11 @@ void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu) > > * The kernel may decide to run userspace after calling vcpu_put, so > > * we reset cntvoff to 0 to ensure a consistent read between user > > * accesses to the virtual counter and kernel access to the physical > > - * counter. > > + * counter of non-VHE case. For VHE, the virtual counter uses a fixed > > + * virtual offset of zero, so no need to zero CNTVOFF_EL2 register. > > */ > > - set_cntvoff(0); > > + if (!has_vhe()) > > + set_cntvoff(0); > > } > > > > /* > > I'm okay with this change. I don't think there's a huge gain here > though. > > Marc, any thoughts or concerns? None. I don't think this brings any visible performance gain, but hey, why not. Acked-by: Marc Zyngier <marc.zyngier@arm.com> M.
diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c index 70268c0..86eca324 100644 --- a/virt/kvm/arm/arch_timer.c +++ b/virt/kvm/arm/arch_timer.c @@ -541,9 +541,11 @@ void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu) * The kernel may decide to run userspace after calling vcpu_put, so * we reset cntvoff to 0 to ensure a consistent read between user * accesses to the virtual counter and kernel access to the physical - * counter. + * counter of non-VHE case. For VHE, the virtual counter uses a fixed + * virtual offset of zero, so no need to zero CNTVOFF_EL2 register. */ - set_cntvoff(0); + if (!has_vhe()) + set_cntvoff(0); } /*
In AArch64/AArch32, the virtual counter uses a fixed virtual offset of zero in the following situations as per ARMv8 specifications: 1) HCR_EL2.E2H is 1, and CNTVCT_EL0/CNTVCT are read from EL2. 2) HCR_EL2.{E2H, TGE} is {1, 1}, and either: — CNTVCT_EL0 is read from Non-secure EL0 or EL2. — CNTVCT is read from Non-secure EL0. So, no need to zero CNTVOFF_EL2/CNTVOFF for VHE case. Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org> --- virt/kvm/arm/arch_timer.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)