On 17/09/2015 16:46, Marc Zyngier wrote:
> When running a guest with the architected timer disabled (with QEMU and
> the kernel_irqchip=off option, for example), it is important to make
> sure the timer gets turned off. Otherwise, the guest may try to
> enable it anyway, leading to a screaming HW interrupt.
>
> The fix is to unconditionally turn off the virtual timer on guest
> exit.
>
> Cc: [email protected]
> Reviewed-by: Christoffer Dall <[email protected]>
> Signed-off-by: Marc Zyngier <[email protected]>
> ---
> arch/arm64/kvm/hyp.S | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
> index 39aa322..60a83e2 100644
> --- a/arch/arm64/kvm/hyp.S
> +++ b/arch/arm64/kvm/hyp.S
> @@ -562,8 +562,6 @@
> mrs x3, cntv_ctl_el0
> and x3, x3, #3
> str w3, [x0, #VCPU_TIMER_CNTV_CTL]
> - bic x3, x3, #1 // Clear Enable
> - msr cntv_ctl_el0, x3
>
> isb
>
> @@ -571,6 +569,9 @@
> str x3, [x0, #VCPU_TIMER_CNTV_CVAL]
>
> 1:
> + // Disable the virtual timer
> + msr cntv_ctl_el0, xzr
> +
> // Allow physical timer/counter access for the host
> mrs x2, cnthctl_el2
> orr x2, x2, #3
>
It looks like here in restore_timer_state:
ldr w2, [x0, #VCPU_TIMER_CNTV_CTL]
and x2, x2, #3
msr cntv_ctl_el0, x2
the "and" would be unnecessary if kvm_arm_timer_set_reg remembered to
do it. Something like this, which would also make the code more
consistent between arm and arm64...
diff --git a/arch/arm/kvm/interrupts_head.S b/arch/arm/kvm/interrupts_head.S
index 702740d37465..93e322b4d242 100644
--- a/arch/arm/kvm/interrupts_head.S
+++ b/arch/arm/kvm/interrupts_head.S
@@ -514,6 +514,7 @@ ARM_BE8(rev r6, r6 )
beq 1f
mrc p15, 0, r2, c14, c3, 1 @ CNTV_CTL
+ and r2, r2, #3
str r2, [vcpu, #VCPU_TIMER_CNTV_CTL]
bic r2, #1 @ Clear ENABLE
mcr p15, 0, r2, c14, c3, 1 @ CNTV_CTL
@@ -566,7 +567,6 @@ ARM_BE8(rev r6, r6 )
isb
ldr r2, [vcpu, #VCPU_TIMER_CNTV_CTL]
- and r2, r2, #3
mcr p15, 0, r2, c14, c3, 1 @ CNTV_CTL
1:
.endm
diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
index 10915aaf0b01..bfcd3f3a947b 100644
--- a/arch/arm64/kvm/hyp.S
+++ b/arch/arm64/kvm/hyp.S
@@ -887,7 +887,6 @@ alternative_endif
isb
ldr w2, [x0, #VCPU_TIMER_CNTV_CTL]
- and x2, x2, #3
msr cntv_ctl_el0, x2
1:
.endm
diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
index 98c95f2fcba4..9b03c9f5abbf 100644
--- a/virt/kvm/arm/arch_timer.c
+++ b/virt/kvm/arm/arch_timer.c
@@ -218,7 +218,7 @@ int kvm_arm_timer_set_reg(struct kvm_vcpu *vcpu, u64 regid,
u64 value)
switch (regid) {
case KVM_REG_ARM_TIMER_CTL:
- timer->cntv_ctl = value;
+ timer->cntv_ctl = value & (ARCH_TIMER_CTRL_IT_MASK |
ARCH_TIMER_CTRL_ENABLE);
break;
case KVM_REG_ARM_TIMER_CNT:
vcpu->kvm->arch.timer.cntvoff = kvm_phys_timer_read() - value;
--
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