[PATCH v6 13/21] KVM: arm64: Allow userspace to configure a vCPU's virtual offset

[Andrew Jones]

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 at google.com>
> ---
>  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 at redhat.com>