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@xxxxxxxxxxxxxx>
> ---
> 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
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