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>
Reviewed-by: Andrew Jones <drjones@xxxxxxxxxx>
---
Documentation/virt/kvm/api.rst | 10 ++++++++++
arch/arm64/include/uapi/asm/kvm.h | 1 +
arch/arm64/kvm/arch_timer.c | 23 +++++++++++++++++++++++
arch/arm64/kvm/guest.c | 6 +++++-
include/kvm/arm_arch_timer.h | 1 +
5 files changed, 40 insertions(+), 1 deletion(-)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index dae68e68ca23..adb04046a752 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -2463,6 +2463,16 @@ 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_CNT 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 cf2f4a034dbe..9d9bac3ec40e 100644
--- a/arch/arm64/kvm/arch_timer.c
+++ b/arch/arm64/kvm/arch_timer.c
@@ -92,6 +92,18 @@ static u64 timer_get_offset(struct arch_timer_context *ctxt)
}
}
+static u64 timer_get_guest_offset(struct arch_timer_context *ctxt)
+{
+ struct kvm_vcpu *vcpu = ctxt->vcpu;
+
+ switch (arch_timer_ctx_index(ctxt)) {
+ case TIMER_VTIMER:
+ return __vcpu_sys_reg(vcpu, CNTVOFF_EL2);
+ default:
+ return 0;
+ }
+}
+
static void timer_set_ctl(struct arch_timer_context *ctxt, u32 ctl)
{
struct kvm_vcpu *vcpu = ctxt->vcpu;
@@ -852,6 +864,10 @@ 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);
@@ -896,6 +912,9 @@ 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);
@@ -933,6 +952,10 @@ 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_guest_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 {
--
2.33.0.rc1.237.g0d66db33f3-goog
_______________________________________________
kvmarm mailing list
kvmarm@xxxxxxxxxxxxxxxxxxxxx
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
