diff mbox series

[v8,4/8] KVM: arm64: Allow userspace to configure a vCPU's virtual offset

Message ID 20210916181510.963449-5-oupton@google.com (mailing list archive)
State New, archived
Headers show
Series KVM: arm64: Add idempotent controls to migrate guest counter | expand

Commit Message

Oliver Upton Sept. 16, 2021, 6:15 p.m. UTC 
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@google.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
---
 Documentation/virt/kvm/api.rst    | 23 +++++++++++++++++++++++
 arch/arm64/include/asm/kvm_host.h |  3 +++
 arch/arm64/include/uapi/asm/kvm.h |  1 +
 arch/arm64/kvm/arch_timer.c       | 23 +++++++++++++++++++++++
 arch/arm64/kvm/arm.c              |  5 +++++
 arch/arm64/kvm/guest.c            | 21 +++++++++++++++++----
 include/kvm/arm_arch_timer.h      |  1 +
 include/uapi/linux/kvm.h          |  1 +
 8 files changed, 74 insertions(+), 4 deletions(-)
diff mbox series

Patch

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index a6729c8cf063..5136e61d7587 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>
@@ -7265,3 +7275,16 @@  The argument to KVM_ENABLE_CAP is also a bitmask, and must be a subset
 of the result of KVM_CHECK_EXTENSION.  KVM will forward to userspace
 the hypercalls whose corresponding bit is in the argument, and return
 ENOSYS for the others.
+
+8.35 KVM_CAP_ARM_VTIMER_OFFSET
+------------------------------
+
+:Capability: KVM_CAP_ARM_VTIMER_OFFSET
+:Architectures: arm64
+:Type: vm
+
+This capability, if enabled, will cause KVM to expose the
+KVM_REG_ARM_TIMER_OFFSET register offset through the
+KVM_{GET,SET}_ONE_REG and KVM_GET_REG_LIST ioctls. Implementing VMMs
+must observe the warning prescribed in section 4.68 with regard to the
+mixed use of timer registers.
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index f8be56d5342b..dd4f6737421c 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -136,6 +136,9 @@  struct kvm_arch {
 
 	/* Memory Tagging Extension enabled for the guest */
 	bool mte_enabled;
+
+	/* KVM_REG_ARM_TIMER_OFFSET enabled for the guest */
+	bool vtimer_offset_enabled;
 };
 
 struct kvm_vcpu_fault_info {
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/arm.c b/arch/arm64/kvm/arm.c
index fe102cd2e518..a562b36f28e2 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -101,6 +101,10 @@  int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 		}
 		mutex_unlock(&kvm->lock);
 		break;
+	case KVM_CAP_ARM_VTIMER_OFFSET:
+		r = 0;
+		kvm->arch.vtimer_offset_enabled = true;
+		break;
 	default:
 		r = -EINVAL;
 		break;
@@ -215,6 +219,7 @@  int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_SET_GUEST_DEBUG:
 	case KVM_CAP_VCPU_ATTRIBUTES:
 	case KVM_CAP_PTP_KVM:
+	case KVM_CAP_ARM_VTIMER_OFFSET:
 		r = 1;
 		break;
 	case KVM_CAP_SET_GUEST_DEBUG2:
diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
index a13a79f5e0e2..098e87451fa5 100644
--- a/arch/arm64/kvm/guest.c
+++ b/arch/arm64/kvm/guest.c
@@ -590,16 +590,23 @@  static unsigned long num_core_regs(const struct kvm_vcpu *vcpu)
 
 static inline unsigned long num_timer_regs(struct kvm_vcpu *vcpu)
 {
-	return 3;
+	unsigned long nr_regs = 3;
+
+	if (vcpu->kvm->arch.vtimer_offset_enabled)
+		nr_regs++;
+
+	return nr_regs;
 }
 
-static bool is_timer_reg(u64 index)
+static bool is_timer_reg(struct kvm_vcpu *vcpu, u64 index)
 {
 	switch (index) {
 	case KVM_REG_ARM_TIMER_CTL:
 	case KVM_REG_ARM_TIMER_CNT:
 	case KVM_REG_ARM_TIMER_CVAL:
 		return true;
+	case KVM_REG_ARM_TIMER_OFFSET:
+		return vcpu->kvm->arch.vtimer_offset_enabled;
 	}
 	return false;
 }
@@ -615,6 +622,12 @@  static int copy_timer_indices(struct kvm_vcpu *vcpu, u64 __user *uindices)
 	if (put_user(KVM_REG_ARM_TIMER_CVAL, uindices))
 		return -EFAULT;
 
+	if (vcpu->kvm->arch.vtimer_offset_enabled) {
+		uindices++;
+		if (put_user(KVM_REG_ARM_TIMER_OFFSET, uindices))
+			return -EFAULT;
+	}
+
 	return 0;
 }
 
@@ -763,7 +776,7 @@  int kvm_arm_get_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
 	case KVM_REG_ARM64_SVE:	return get_sve_reg(vcpu, reg);
 	}
 
-	if (is_timer_reg(reg->id))
+	if (is_timer_reg(vcpu, reg->id))
 		return get_timer_reg(vcpu, reg);
 
 	return kvm_arm_sys_reg_get_reg(vcpu, reg);
@@ -781,7 +794,7 @@  int kvm_arm_set_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
 	case KVM_REG_ARM64_SVE:	return set_sve_reg(vcpu, reg);
 	}
 
-	if (is_timer_reg(reg->id))
+	if (is_timer_reg(vcpu, reg->id))
 		return set_timer_reg(vcpu, reg);
 
 	return kvm_arm_sys_reg_set_reg(vcpu, reg);
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 {
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index a067410ebea5..70c76537417e 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1112,6 +1112,7 @@  struct kvm_ppc_resize_hpt {
 #define KVM_CAP_BINARY_STATS_FD 203
 #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
 #define KVM_CAP_ARM_MTE 205
+#define KVM_CAP_ARM_VTIMER_OFFSET 206
 
 #ifdef KVM_CAP_IRQ_ROUTING