Re: [PATCH v2 2/2] KVM: arm64: timers: Save restore CVAL of a ptimer across guest entry and exits

Marc Zyngier
2023-09-18T11:32:40Z

On Fri, 15 Sep 2023 10:57:46 +0100,
Ganapatrao Kulkarni <gankulkarni@os.amperecomputing.com> wrote:
>
> This patch did not work.
> After adding changes as in below diff, it is started working.

Thanks for looking into this.

>
> diff --git a/arch/arm64/kvm/hyp/vhe/switch.c
> b/arch/arm64/kvm/hyp/vhe/switch.c
> index b0b07658f77d..91d2cfb03e26 100644
> --- a/arch/arm64/kvm/hyp/vhe/switch.c
> +++ b/arch/arm64/kvm/hyp/vhe/switch.c
> @@ -117,7 +117,7 @@ static void __activate_traps(struct kvm_vcpu *vcpu)
> val = __vcpu_sys_reg(vcpu, CNTHP_CVAL_EL2);
>
> if (map.direct_ptimer) {
> - write_sysreg_s(val, SYS_CNTP_CVAL_EL0);
> + write_sysreg_el0(val, SYS_CNTP_CVAL);

Duh, of course. Silly me.

> isb();
> }
> }
> @@ -161,8 +161,6 @@ static void __deactivate_traps(struct kvm_vcpu *vcpu)
>
> ___deactivate_traps(vcpu);
>
> - write_sysreg(HCR_HOST_VHE_FLAGS, hcr_el2);
> -
> if (has_cntpoff()) {
> struct timer_map map;
> u64 val, offset;
> @@ -173,7 +171,7 @@ static void __deactivate_traps(struct kvm_vcpu *vcpu)
> * We're exiting the guest. Save the latest CVAL value
> * to memory and apply the offset now that TGE is set.
> */
> - val = read_sysreg_s(SYS_CNTP_CVAL_EL0);
> + val = read_sysreg_el0(SYS_CNTP_CVAL);
> if (map.direct_ptimer == vcpu_ptimer(vcpu))
> __vcpu_sys_reg(vcpu, CNTP_CVAL_EL0) = val;
> if (map.direct_ptimer == vcpu_hptimer(vcpu))
> @@ -182,12 +180,13 @@ static void __deactivate_traps(struct kvm_vcpu *vcpu)
> offset = read_sysreg_s(SYS_CNTPOFF_EL2);
>
> if (map.direct_ptimer && offset) {
> - offset = read_sysreg_s(SYS_CNTPOFF_EL2);
> - write_sysreg_s(val + offset, SYS_CNTP_CVAL_EL0);
> + write_sysreg_el0(val + offset, SYS_CNTP_CVAL);
> isb();
> }
> }
>
> + write_sysreg(HCR_HOST_VHE_FLAGS, hcr_el2);

Why moving the HCR_EL2 update? I don't grok what it changes. Or is it
that you end-up with spurious interrupts because your GIC is slow to
retire interrupts that are transiently pending?

Thanks,

M.

--
Without deviation from the norm, progress is not possible.