[PATCH v6 17/21] KVM: arm64: Allow userspace to configure a guest's counter-timer offset

[Oliver Upton <oupton@google.com>]

Presently, KVM provides no facilities for correctly migrating a guest
that depends on the physical counter-timer. Whie most guests (barring
NV, of course) should not depend on the physical counter-timer, an
operator may wish to provide a consistent view of the physical
counter-timer across migrations.

Provide userspace with a new vCPU attribute to modify the guest
counter-timer offset. Unlike KVM_REG_ARM_TIMER_OFFSET, this attribute is
hidden from the guest's architectural state. The value offsets *both*
the virtual and physical counter-timer views for the guest. Only support
this attribute on ECV systems as ECV is required for hardware offsetting
of the physical counter-timer.

Signed-off-by: Oliver Upton <oupton@google.com>
---
 Documentation/virt/kvm/devices/vcpu.rst |  28 ++++++
 arch/arm64/include/asm/kvm_asm.h        |   2 +
 arch/arm64/include/asm/sysreg.h         |   2 +
 arch/arm64/include/uapi/asm/kvm.h       |   1 +
 arch/arm64/kvm/arch_timer.c             | 122 +++++++++++++++++++++++-
 arch/arm64/kvm/hyp/nvhe/hyp-main.c      |   6 ++
 arch/arm64/kvm/hyp/nvhe/timer-sr.c      |   5 +
 arch/arm64/kvm/hyp/vhe/timer-sr.c       |   5 +
 include/clocksource/arm_arch_timer.h    |   1 +
 9 files changed, 169 insertions(+), 3 deletions(-)

diff --git a/Documentation/virt/kvm/devices/vcpu.rst b/Documentation/virt/kvm/devices/vcpu.rst
index 3b399d727c11..3ba35b9d9d03 100644
--- a/Documentation/virt/kvm/devices/vcpu.rst
+++ b/Documentation/virt/kvm/devices/vcpu.rst
@@ -139,6 +139,34 @@ configured values on other VCPUs.  Userspace should configure the interrupt
 numbers on at least one VCPU after creating all VCPUs and before running any
 VCPUs.
 
+2.2. ATTRIBUTE: KVM_ARM_VCPU_TIMER_OFFSET
+-----------------------------------------
+
+:Parameters: in kvm_device_attr.addr the address for the timer offset is a
+             pointer to a __u64
+
+Returns:
+
+	 ======= ==================================
+	 -EFAULT Error reading/writing the provided
+		 parameter address
+	 -ENXIO  Timer offsetting not implemented
+	 ======= ==================================
+
+Specifies the guest's counter-timer offset from the host's virtual counter.
+The guest's physical counter value is then derived by the following
+equation:
+
+  guest_cntpct = host_cntvct - KVM_ARM_VCPU_TIMER_OFFSET
+
+The guest's virtual counter value is derived by the following equation:
+
+  guest_cntvct = host_cntvct - KVM_REG_ARM_TIMER_OFFSET
+			- KVM_ARM_VCPU_TIMER_OFFSET
+
+KVM does not allow the use of varying offset values for different vCPUs;
+the last written offset value will be broadcasted to all vCPUs in a VM.
+
 3. GROUP: KVM_ARM_VCPU_PVTIME_CTRL
 ==================================
 
diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 9f0bf2109be7..ab1c8fdb0177 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -65,6 +65,7 @@
 #define __KVM_HOST_SMCCC_FUNC___pkvm_prot_finalize		19
 #define __KVM_HOST_SMCCC_FUNC___pkvm_mark_hyp			20
 #define __KVM_HOST_SMCCC_FUNC___kvm_adjust_pc			21
+#define __KVM_HOST_SMCCC_FUNC___kvm_timer_set_cntpoff		22
 
 #ifndef __ASSEMBLY__
 
@@ -200,6 +201,7 @@ extern void __kvm_tlb_flush_vmid_ipa(struct kvm_s2_mmu *mmu, phys_addr_t ipa,
 extern void __kvm_tlb_flush_vmid(struct kvm_s2_mmu *mmu);
 
 extern void __kvm_timer_set_cntvoff(u64 cntvoff);
+extern void __kvm_timer_set_cntpoff(u64 cntpoff);
 
 extern int __kvm_vcpu_run(struct kvm_vcpu *vcpu);
 
diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index 4dfc44066dfb..c34672aa65b9 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -586,6 +586,8 @@
 #define SYS_ICH_LR14_EL2		__SYS__LR8_EL2(6)
 #define SYS_ICH_LR15_EL2		__SYS__LR8_EL2(7)
 
+#define SYS_CNTPOFF_EL2			sys_reg(3, 4, 14, 0, 6)
+
 /* VHE encodings for architectural EL0/1 system registers */
 #define SYS_SCTLR_EL12			sys_reg(3, 5, 1, 0, 0)
 #define SYS_CPACR_EL12			sys_reg(3, 5, 1, 0, 2)
diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index 949a31bc10f0..15150f8224a1 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -366,6 +366,7 @@ struct kvm_arm_copy_mte_tags {
 #define KVM_ARM_VCPU_TIMER_CTRL		1
 #define   KVM_ARM_VCPU_TIMER_IRQ_VTIMER		0
 #define   KVM_ARM_VCPU_TIMER_IRQ_PTIMER		1
+#define   KVM_ARM_VCPU_TIMER_OFFSET		2
 #define KVM_ARM_VCPU_PVTIME_CTRL	2
 #define   KVM_ARM_VCPU_PVTIME_IPA	0
 
diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
index a8815b09da3e..f15058612994 100644
--- a/arch/arm64/kvm/arch_timer.c
+++ b/arch/arm64/kvm/arch_timer.c
@@ -85,11 +85,15 @@ u64 timer_get_cval(struct arch_timer_context *ctxt)
 static u64 timer_get_offset(struct arch_timer_context *ctxt)
 {
 	struct kvm_vcpu *vcpu = ctxt->vcpu;
+	struct arch_timer_cpu *timer = vcpu_timer(vcpu);
 
 	switch(arch_timer_ctx_index(ctxt)) {
 	case TIMER_VTIMER:
+	case TIMER_PTIMER:
 		return ctxt->host_offset;
 	default:
+		WARN_ONCE(1, "unrecognized timer %ld\n",
+			  arch_timer_ctx_index(ctxt));
 		return 0;
 	}
 }
@@ -144,6 +148,7 @@ static void timer_set_offset(struct arch_timer_context *ctxt, u64 offset)
 
 	switch(arch_timer_ctx_index(ctxt)) {
 	case TIMER_VTIMER:
+	case TIMER_PTIMER:
 		ctxt->host_offset = offset;
 		break;
 	default:
@@ -572,6 +577,11 @@ static void set_cntvoff(u64 cntvoff)
 	kvm_call_hyp(__kvm_timer_set_cntvoff, cntvoff);
 }
 
+static void set_cntpoff(u64 cntpoff)
+{
+	kvm_call_hyp(__kvm_timer_set_cntpoff, cntpoff);
+}
+
 static inline void set_timer_irq_phys_active(struct arch_timer_context *ctx, bool active)
 {
 	int r;
@@ -647,6 +657,8 @@ void kvm_timer_vcpu_load(struct kvm_vcpu *vcpu)
 	}
 
 	set_cntvoff(timer_get_offset(map.direct_vtimer));
+	if (cpus_have_const_cap(ARM64_ECV))
+		set_cntpoff(timer_get_offset(vcpu_ptimer(vcpu)));
 
 	kvm_timer_unblocking(vcpu);
 
@@ -814,6 +826,22 @@ static void update_vtimer_cntvoff(struct kvm_vcpu *vcpu, u64 cntvoff)
 	mutex_unlock(&kvm->lock);
 }
 
+static void update_ptimer_cntpoff(struct kvm_vcpu *vcpu, u64 cntpoff)
+{
+	struct kvm *kvm = vcpu->kvm;
+	u64 cntvoff;
+
+	mutex_lock(&kvm->lock);
+
+	/* adjustments to the physical offset also affect vtimer */
+	cntvoff = timer_get_offset(vcpu_vtimer(vcpu));
+	cntvoff += cntpoff - timer_get_offset(vcpu_ptimer(vcpu));
+
+	update_timer_offset(vcpu, TIMER_PTIMER, cntpoff, false);
+	update_timer_offset(vcpu, TIMER_VTIMER, cntvoff, false);
+	mutex_unlock(&kvm->lock);
+}
+
 void kvm_timer_vcpu_init(struct kvm_vcpu *vcpu)
 {
 	struct arch_timer_cpu *timer = vcpu_timer(vcpu);
@@ -932,6 +960,29 @@ u64 kvm_arm_timer_get_reg(struct kvm_vcpu *vcpu, u64 regid)
 	return (u64)-1;
 }
 
+/**
+ * kvm_arm_timer_read_offset - returns the guest value of CNTVOFF_EL2.
+ * @vcpu: the vcpu pointer
+ *
+ * Computes the guest value of CNTVOFF_EL2 by subtracting the physical
+ * counter offset. Note that KVM defines CNTVOFF_EL2 as the offset from the
+ * guest's physical counter-timer, not the host's.
+ *
+ * Returns: the guest value for CNTVOFF_EL2
+ */
+static u64 kvm_arm_timer_read_offset(struct kvm_vcpu *vcpu)
+{
+	struct kvm *kvm = vcpu->kvm;
+	u64 offset;
+
+	mutex_lock(&kvm->lock);
+	offset = timer_get_offset(vcpu_vtimer(vcpu)) -
+			timer_get_offset(vcpu_ptimer(vcpu));
+	mutex_unlock(&kvm->lock);
+
+	return offset;
+}
+
 static u64 kvm_arm_timer_read(struct kvm_vcpu *vcpu,
 			      struct arch_timer_context *timer,
 			      enum kvm_arch_timer_regs treg)
@@ -957,7 +1008,7 @@ static u64 kvm_arm_timer_read(struct kvm_vcpu *vcpu,
 		break;
 
 	case TIMER_REG_OFFSET:
-		val = timer_get_offset(timer);
+		val = kvm_arm_timer_read_offset(vcpu);
 		break;
 
 	default:
@@ -1350,6 +1401,9 @@ void kvm_timer_init_vhe(void)
 	val = read_sysreg(cnthctl_el2);
 	val |= (CNTHCTL_EL1PCEN << cnthctl_shift);
 	val |= (CNTHCTL_EL1PCTEN << cnthctl_shift);
+
+	if (cpus_have_const_cap(ARM64_ECV))
+		val |= CNTHCTL_ECV;
 	write_sysreg(val, cnthctl_el2);
 }
 
@@ -1364,7 +1418,8 @@ static void set_timer_irqs(struct kvm *kvm, int vtimer_irq, int ptimer_irq)
 	}
 }
 
-int kvm_arm_timer_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
+static int kvm_arm_timer_set_attr_irq(struct kvm_vcpu *vcpu,
+				      struct kvm_device_attr *attr)
 {
 	int __user *uaddr = (int __user *)(long)attr->addr;
 	struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
@@ -1397,7 +1452,37 @@ int kvm_arm_timer_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 	return 0;
 }
 
-int kvm_arm_timer_get_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
+static int kvm_arm_timer_set_attr_offset(struct kvm_vcpu *vcpu,
+					 struct kvm_device_attr *attr)
+{
+	u64 __user *uaddr = (u64 __user *)(long)attr->addr;
+	u64 offset;
+
+	if (!cpus_have_const_cap(ARM64_ECV))
+		return -ENXIO;
+
+	if (get_user(offset, uaddr))
+		return -EFAULT;
+
+	update_ptimer_cntpoff(vcpu, offset);
+	return 0;
+}
+
+int kvm_arm_timer_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
+{
+	switch (attr->attr) {
+	case KVM_ARM_VCPU_TIMER_IRQ_VTIMER:
+	case KVM_ARM_VCPU_TIMER_IRQ_PTIMER:
+		return kvm_arm_timer_set_attr_irq(vcpu, attr);
+	case KVM_ARM_VCPU_TIMER_OFFSET:
+		return kvm_arm_timer_set_attr_offset(vcpu, attr);
+	default:
+		return -ENXIO;
+	}
+}
+
+static int kvm_arm_timer_get_attr_irq(struct kvm_vcpu *vcpu,
+				      struct kvm_device_attr *attr)
 {
 	int __user *uaddr = (int __user *)(long)attr->addr;
 	struct arch_timer_context *timer;
@@ -1418,12 +1503,43 @@ int kvm_arm_timer_get_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 	return put_user(irq, uaddr);
 }
 
+static int kvm_arm_timer_get_attr_offset(struct kvm_vcpu *vcpu,
+					 struct kvm_device_attr *attr)
+{
+	u64 __user *uaddr = (u64 __user *)(long)attr->addr;
+	u64 offset;
+
+	if (!cpus_have_const_cap(ARM64_ECV))
+		return -ENXIO;
+
+	offset = timer_get_offset(vcpu_ptimer(vcpu));
+	return put_user(offset, uaddr);
+}
+
+int kvm_arm_timer_get_attr(struct kvm_vcpu *vcpu,
+			   struct kvm_device_attr *attr)
+{
+	switch (attr->attr) {
+	case KVM_ARM_VCPU_TIMER_IRQ_VTIMER:
+	case KVM_ARM_VCPU_TIMER_IRQ_PTIMER:
+		return kvm_arm_timer_get_attr_irq(vcpu, attr);
+	case KVM_ARM_VCPU_TIMER_OFFSET:
+		return kvm_arm_timer_get_attr_offset(vcpu, attr);
+	default:
+		return -ENXIO;
+	}
+}
+
 int kvm_arm_timer_has_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 {
 	switch (attr->attr) {
 	case KVM_ARM_VCPU_TIMER_IRQ_VTIMER:
 	case KVM_ARM_VCPU_TIMER_IRQ_PTIMER:
 		return 0;
+	case KVM_ARM_VCPU_TIMER_OFFSET:
+		if (cpus_have_const_cap(ARM64_ECV))
+			return 0;
+		break;
 	}
 
 	return -ENXIO;
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 1632f001f4ed..cfa923df3af6 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -68,6 +68,11 @@ static void handle___kvm_timer_set_cntvoff(struct kvm_cpu_context *host_ctxt)
 	__kvm_timer_set_cntvoff(cpu_reg(host_ctxt, 1));
 }
 
+static void handle___kvm_timer_set_cntpoff(struct kvm_cpu_context *host_ctxt)
+{
+	__kvm_timer_set_cntpoff(cpu_reg(host_ctxt, 1));
+}
+
 static void handle___kvm_enable_ssbs(struct kvm_cpu_context *host_ctxt)
 {
 	u64 tmp;
@@ -197,6 +202,7 @@ static const hcall_t host_hcall[] = {
 	HANDLE_FUNC(__pkvm_create_private_mapping),
 	HANDLE_FUNC(__pkvm_prot_finalize),
 	HANDLE_FUNC(__pkvm_mark_hyp),
+	HANDLE_FUNC(__kvm_timer_set_cntpoff),
 };
 
 static void handle_host_hcall(struct kvm_cpu_context *host_ctxt)
diff --git a/arch/arm64/kvm/hyp/nvhe/timer-sr.c b/arch/arm64/kvm/hyp/nvhe/timer-sr.c
index 9072e71693ba..5b8b4cd02506 100644
--- a/arch/arm64/kvm/hyp/nvhe/timer-sr.c
+++ b/arch/arm64/kvm/hyp/nvhe/timer-sr.c
@@ -15,6 +15,11 @@ void __kvm_timer_set_cntvoff(u64 cntvoff)
 	write_sysreg(cntvoff, cntvoff_el2);
 }
 
+void __kvm_timer_set_cntpoff(u64 cntpoff)
+{
+	write_sysreg_s(cntpoff, SYS_CNTPOFF_EL2);
+}
+
 /*
  * Should only be called on non-VHE systems.
  * VHE systems use EL2 timers and configure EL1 timers in kvm_timer_init_vhe().
diff --git a/arch/arm64/kvm/hyp/vhe/timer-sr.c b/arch/arm64/kvm/hyp/vhe/timer-sr.c
index 4cda674a8be6..231e16a071a5 100644
--- a/arch/arm64/kvm/hyp/vhe/timer-sr.c
+++ b/arch/arm64/kvm/hyp/vhe/timer-sr.c
@@ -10,3 +10,8 @@ void __kvm_timer_set_cntvoff(u64 cntvoff)
 {
 	write_sysreg(cntvoff, cntvoff_el2);
 }
+
+void __kvm_timer_set_cntpoff(u64 cntpoff)
+{
+	write_sysreg_s(cntpoff, SYS_CNTPOFF_EL2);
+}
diff --git a/include/clocksource/arm_arch_timer.h b/include/clocksource/arm_arch_timer.h
index 73c7139c866f..7252ffa3d675 100644
--- a/include/clocksource/arm_arch_timer.h
+++ b/include/clocksource/arm_arch_timer.h
@@ -21,6 +21,7 @@
 #define CNTHCTL_EVNTEN			(1 << 2)
 #define CNTHCTL_EVNTDIR			(1 << 3)
 #define CNTHCTL_EVNTI			(0xF << 4)
+#define CNTHCTL_ECV			(1 << 12)
 
 enum arch_timer_reg {
 	ARCH_TIMER_REG_CTRL,
-- 
2.32.0.605.g8dce9f2422-goog


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