On Wed, Aug 04, 2021 at 08:58:11AM +0000, Oliver Upton wrote:
> Allow userspace to access the guest's virtual counter-timer offset
> through the ONE_REG interface. The value read or written is defined to
> be an offset from the guest's physical counter-timer. Add some
> documentation to clarify how a VMM should use this and the existing
> CNTVCT_EL0.
>
> Signed-off-by: Oliver Upton <oupton@xxxxxxxxxx>
> ---
> Documentation/virt/kvm/api.rst | 10 ++++++++++
> arch/arm64/include/uapi/asm/kvm.h | 1 +
> arch/arm64/kvm/arch_timer.c | 11 +++++++++++
> arch/arm64/kvm/guest.c | 6 +++++-
> include/kvm/arm_arch_timer.h | 1 +
> 5 files changed, 28 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 8d4a3471ad9e..28a65dc89985 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -2487,6 +2487,16 @@ arm64 system registers have the following id bit patterns::
> derived from the register encoding for CNTV_CVAL_EL0. As this is
> API, it must remain this way.
>
> +.. warning::
> +
> + The value of KVM_REG_ARM_TIMER_OFFSET is defined as an offset from
> + the guest's view of the physical counter-timer.
> +
> + Userspace should use either KVM_REG_ARM_TIMER_OFFSET or
> + KVM_REG_ARM_TIMER_CVAL to pause and resume a guest's virtual
> + counter-timer. Mixed use of these registers could result in an
> + unpredictable guest counter value.
> +
> arm64 firmware pseudo-registers have the following bit pattern::
>
> 0x6030 0000 0014 <regno:16>
> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> index b3edde68bc3e..949a31bc10f0 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -255,6 +255,7 @@ struct kvm_arm_copy_mte_tags {
> #define KVM_REG_ARM_TIMER_CTL ARM64_SYS_REG(3, 3, 14, 3, 1)
> #define KVM_REG_ARM_TIMER_CVAL ARM64_SYS_REG(3, 3, 14, 0, 2)
> #define KVM_REG_ARM_TIMER_CNT ARM64_SYS_REG(3, 3, 14, 3, 2)
> +#define KVM_REG_ARM_TIMER_OFFSET ARM64_SYS_REG(3, 4, 14, 0, 3)
>
> /* KVM-as-firmware specific pseudo-registers */
> #define KVM_REG_ARM_FW (0x0014 << KVM_REG_ARM_COPROC_SHIFT)
> diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
> index 4c2b763a8849..a8815b09da3e 100644
> --- a/arch/arm64/kvm/arch_timer.c
> +++ b/arch/arm64/kvm/arch_timer.c
> @@ -868,6 +868,10 @@ int kvm_arm_timer_set_reg(struct kvm_vcpu *vcpu, u64 regid, u64 value)
> timer = vcpu_vtimer(vcpu);
> kvm_arm_timer_write(vcpu, timer, TIMER_REG_CVAL, value);
> break;
> + case KVM_REG_ARM_TIMER_OFFSET:
> + timer = vcpu_vtimer(vcpu);
> + update_vtimer_cntvoff(vcpu, value);
> + break;
> case KVM_REG_ARM_PTIMER_CTL:
> timer = vcpu_ptimer(vcpu);
> kvm_arm_timer_write(vcpu, timer, TIMER_REG_CTL, value);
> @@ -912,6 +916,9 @@ u64 kvm_arm_timer_get_reg(struct kvm_vcpu *vcpu, u64 regid)
> case KVM_REG_ARM_TIMER_CVAL:
> return kvm_arm_timer_read(vcpu,
> vcpu_vtimer(vcpu), TIMER_REG_CVAL);
> + case KVM_REG_ARM_TIMER_OFFSET:
> + return kvm_arm_timer_read(vcpu,
> + vcpu_vtimer(vcpu), TIMER_REG_OFFSET);
> case KVM_REG_ARM_PTIMER_CTL:
> return kvm_arm_timer_read(vcpu,
> vcpu_ptimer(vcpu), TIMER_REG_CTL);
> @@ -949,6 +956,10 @@ static u64 kvm_arm_timer_read(struct kvm_vcpu *vcpu,
> val = kvm_phys_timer_read() - timer_get_offset(timer);
> break;
>
> + case TIMER_REG_OFFSET:
> + val = timer_get_offset(timer);
> + break;
> +
> default:
> BUG();
> }
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index 1dfb83578277..17fc06e2b422 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -591,7 +591,7 @@ static unsigned long num_core_regs(const struct kvm_vcpu *vcpu)
> * ARM64 versions of the TIMER registers, always available on arm64
> */
>
> -#define NUM_TIMER_REGS 3
> +#define NUM_TIMER_REGS 4
>
> static bool is_timer_reg(u64 index)
> {
> @@ -599,6 +599,7 @@ static bool is_timer_reg(u64 index)
> case KVM_REG_ARM_TIMER_CTL:
> case KVM_REG_ARM_TIMER_CNT:
> case KVM_REG_ARM_TIMER_CVAL:
> + case KVM_REG_ARM_TIMER_OFFSET:
> return true;
> }
> return false;
> @@ -614,6 +615,9 @@ static int copy_timer_indices(struct kvm_vcpu *vcpu, u64 __user *uindices)
> uindices++;
> if (put_user(KVM_REG_ARM_TIMER_CVAL, uindices))
> return -EFAULT;
> + uindices++;
> + if (put_user(KVM_REG_ARM_TIMER_OFFSET, uindices))
> + return -EFAULT;
>
> return 0;
> }
> diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h
> index 9d65d4a29f81..615f9314f6a5 100644
> --- a/include/kvm/arm_arch_timer.h
> +++ b/include/kvm/arm_arch_timer.h
> @@ -21,6 +21,7 @@ enum kvm_arch_timer_regs {
> TIMER_REG_CVAL,
> TIMER_REG_TVAL,
> TIMER_REG_CTL,
> + TIMER_REG_OFFSET,
> };
>
> struct arch_timer_context {
> --
> 2.32.0.605.g8dce9f2422-goog
>
Reviewed-by: Andrew Jones <drjones@xxxxxxxxxx>
