Re: [PATCH 47/59] KVM: arm64: nv: Propagate CNTVOFF_EL2 to the virtual EL1 timer

Alexandru Elisei
2019-08-08T09:34:43Z

On 6/21/19 10:38 AM, Marc Zyngier wrote:
> We need to allow a guest hypervisor to virtualize the virtual timer.
> FOr that, let's propagate CNTVOFF_EL2 to the guest's view of that
> timer.
>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
> arch/arm64/include/asm/kvm_host.h | 1 -
> arch/arm64/kvm/sys_regs.c | 8 ++++++--
> include/kvm/arm_arch_timer.h | 1 +
> virt/kvm/arm/arch_timer.c | 12 ++++++++++++
> 4 files changed, 19 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index b7c44adcdbf3..e0fe9acb46bf 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -252,7 +252,6 @@ enum vcpu_sysreg {
> RMR_EL2, /* Reset Management Register */
> CONTEXTIDR_EL2, /* Context ID Register (EL2) */
> TPIDR_EL2, /* EL2 Software Thread ID Register */
> - CNTVOFF_EL2, /* Counter-timer Virtual Offset register */
> CNTHCTL_EL2, /* Counter-timer Hypervisor Control register */
> SP_EL2, /* EL2 Stack Pointer */
>
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 1b8016330a19..2031a59fcf49 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -150,7 +150,6 @@ struct el2_sysreg_map {
> PURE_EL2_SYSREG( RVBAR_EL2 ),
> PURE_EL2_SYSREG( RMR_EL2 ),
> PURE_EL2_SYSREG( TPIDR_EL2 ),
> - PURE_EL2_SYSREG( CNTVOFF_EL2 ),
> PURE_EL2_SYSREG( CNTHCTL_EL2 ),
> PURE_EL2_SYSREG( HPFAR_EL2 ),
> EL2_SYSREG( SCTLR_EL2, SCTLR_EL1, translate_sctlr ),
> @@ -1351,6 +1350,11 @@ static bool access_arch_timer(struct kvm_vcpu *vcpu,
> tmr = TIMER_PTIMER;
> treg = TIMER_REG_CVAL;
> break;
> + case SYS_CNTVOFF_EL2:
> + tmr = TIMER_VTIMER;
> + treg = TIMER_REG_VOFF;
> + break;
> +
> default:
> BUG();
> }
> @@ -2122,7 +2126,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
> { SYS_DESC(SYS_CONTEXTIDR_EL2), access_rw, reset_val, CONTEXTIDR_EL2, 0 },
> { SYS_DESC(SYS_TPIDR_EL2), access_rw, reset_val, TPIDR_EL2, 0 },
>
> - { SYS_DESC(SYS_CNTVOFF_EL2), access_rw, reset_val, CNTVOFF_EL2, 0 },
> + { SYS_DESC(SYS_CNTVOFF_EL2), access_arch_timer },
> { SYS_DESC(SYS_CNTHCTL_EL2), access_rw, reset_val, CNTHCTL_EL2, 0 },
>
> { SYS_DESC(SYS_CNTHP_TVAL_EL2), access_arch_timer },
> diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h
> index 3a5d9255120e..3389606f3029 100644
> --- a/include/kvm/arm_arch_timer.h
> +++ b/include/kvm/arm_arch_timer.h
> @@ -23,6 +23,7 @@ enum kvm_arch_timer_regs {
> TIMER_REG_CVAL,
> TIMER_REG_TVAL,
> TIMER_REG_CTL,
> + TIMER_REG_VOFF,
> };
>
> struct arch_timer_context {
> diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
> index 3d84c240071d..1d53352c7d97 100644
> --- a/virt/kvm/arm/arch_timer.c
> +++ b/virt/kvm/arm/arch_timer.c
> @@ -913,6 +913,10 @@ static u64 kvm_arm_timer_read(struct kvm_vcpu *vcpu,
> val = kvm_phys_timer_read() - timer->cntvoff;
> break;
>
> + case TIMER_REG_VOFF:
> + val = timer->cntvoff;
> + break;
> +
> default:
> BUG();
> }
> @@ -955,6 +959,10 @@ static void kvm_arm_timer_write(struct kvm_vcpu *vcpu,
> timer->cnt_cval = val;
> break;
>
> + case TIMER_REG_VOFF:
> + timer->cntvoff = val;
> + break;
> +
> default:
> BUG();
> }
> @@ -1166,6 +1174,10 @@ int kvm_timer_enable(struct kvm_vcpu *vcpu)
> return -EINVAL;
> }
>
> + /* Nested virtualization requires zero offset for virtual EL2 */
> + if (nested_virt_in_use(vcpu))
> + vcpu_vtimer(vcpu)->cntvoff = 0;

I think this is related to the fact that the virtual offset is treated as 0 when
reading CNTVCT_EL0 from EL2, or from from EL2 and EL0 if E2H, TGE are set
(please correct me if I'm wrong).

However, when the guest runs in virtual EL2, the direct_vtimer is the hvtimer,
so the value that ends up in CNTVOFF_EL2 is vcpu_hvtimer(vcpu)->cntvoff.

Thanks,
Alex
> +
> get_timer_map(vcpu, &map);
>
> ret = kvm_vgic_map_phys_irq(vcpu,