[PATCH v2 01/19] KVM: arm64: timers: Convert per-vcpu virtual offset to a global value
Marc Zyngier
maz at kernel.org
Mon Mar 13 05:48:19 PDT 2023
Having a per-vcpu virtual offset is a pain. It needs to be synchronized
on each update, and expands badly to a setup where different timers can
have different offsets, or have composite offsets (as with NV).
So let's start by replacing the use of the CNTVOFF_EL2 shadow register
(which we want to reclaim for NV anyway), and make the virtual timer
carry a pointer to a VM-wide offset.
This simplifies the code significantly. It also addresses two terrible bugs:
- The use of CNTVOFF_EL2 leads to some nice offset corruption
when the sysreg gets reset, as reported by Joey.
- The kvm mutex is taken from a vcpu ioctl, which goes against
the locking rules...
Reported-by: Joey Gouly <joey.gouly at arm.com>
Reviewed-by: Reiji Watanabe <reijiw at google.com>
Signed-off-by: Marc Zyngier <maz at kernel.org>
Link: https://lore.kernel.org/r/20230224173915.GA17407@e124191.cambridge.arm.com
---
arch/arm64/include/asm/kvm_host.h | 3 +++
arch/arm64/kvm/arch_timer.c | 45 +++++++------------------------
arch/arm64/kvm/hypercalls.c | 2 +-
include/kvm/arm_arch_timer.h | 15 +++++++++++
4 files changed, 29 insertions(+), 36 deletions(-)
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index a1892a8f6032..bcd774d74f34 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -193,6 +193,9 @@ struct kvm_arch {
/* Interrupt controller */
struct vgic_dist vgic;
+ /* Timers */
+ struct arch_timer_vm_data timer_data;
+
/* Mandated version of PSCI */
u32 psci_version;
diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
index 00610477ec7b..e1af4301b913 100644
--- a/arch/arm64/kvm/arch_timer.c
+++ b/arch/arm64/kvm/arch_timer.c
@@ -84,14 +84,10 @@ 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;
+ if (ctxt->offset.vm_offset)
+ return *ctxt->offset.vm_offset;
- switch(arch_timer_ctx_index(ctxt)) {
- case TIMER_VTIMER:
- return __vcpu_sys_reg(vcpu, CNTVOFF_EL2);
- default:
- return 0;
- }
+ return 0;
}
static void timer_set_ctl(struct arch_timer_context *ctxt, u32 ctl)
@@ -128,15 +124,12 @@ static void timer_set_cval(struct arch_timer_context *ctxt, u64 cval)
static void timer_set_offset(struct arch_timer_context *ctxt, u64 offset)
{
- struct kvm_vcpu *vcpu = ctxt->vcpu;
-
- switch(arch_timer_ctx_index(ctxt)) {
- case TIMER_VTIMER:
- __vcpu_sys_reg(vcpu, CNTVOFF_EL2) = offset;
- break;
- default:
+ if (!ctxt->offset.vm_offset) {
WARN(offset, "timer %ld\n", arch_timer_ctx_index(ctxt));
+ return;
}
+
+ WRITE_ONCE(*ctxt->offset.vm_offset, offset);
}
u64 kvm_phys_timer_read(void)
@@ -765,25 +758,6 @@ int kvm_timer_vcpu_reset(struct kvm_vcpu *vcpu)
return 0;
}
-/* Make the updates of cntvoff for all vtimer contexts atomic */
-static void update_vtimer_cntvoff(struct kvm_vcpu *vcpu, u64 cntvoff)
-{
- unsigned long i;
- struct kvm *kvm = vcpu->kvm;
- struct kvm_vcpu *tmp;
-
- mutex_lock(&kvm->lock);
- kvm_for_each_vcpu(i, tmp, kvm)
- timer_set_offset(vcpu_vtimer(tmp), cntvoff);
-
- /*
- * When called from the vcpu create path, the CPU being created is not
- * included in the loop above, so we just set it here as well.
- */
- timer_set_offset(vcpu_vtimer(vcpu), cntvoff);
- mutex_unlock(&kvm->lock);
-}
-
void kvm_timer_vcpu_init(struct kvm_vcpu *vcpu)
{
struct arch_timer_cpu *timer = vcpu_timer(vcpu);
@@ -791,10 +765,11 @@ void kvm_timer_vcpu_init(struct kvm_vcpu *vcpu)
struct arch_timer_context *ptimer = vcpu_ptimer(vcpu);
vtimer->vcpu = vcpu;
+ vtimer->offset.vm_offset = &vcpu->kvm->arch.timer_data.voffset;
ptimer->vcpu = vcpu;
/* Synchronize cntvoff across all vtimers of a VM. */
- update_vtimer_cntvoff(vcpu, kvm_phys_timer_read());
+ timer_set_offset(vtimer, kvm_phys_timer_read());
timer_set_offset(ptimer, 0);
hrtimer_init(&timer->bg_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
@@ -840,7 +815,7 @@ int kvm_arm_timer_set_reg(struct kvm_vcpu *vcpu, u64 regid, u64 value)
break;
case KVM_REG_ARM_TIMER_CNT:
timer = vcpu_vtimer(vcpu);
- update_vtimer_cntvoff(vcpu, kvm_phys_timer_read() - value);
+ timer_set_offset(timer, kvm_phys_timer_read() - value);
break;
case KVM_REG_ARM_TIMER_CVAL:
timer = vcpu_vtimer(vcpu);
diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
index 64c086c02c60..5da884e11337 100644
--- a/arch/arm64/kvm/hypercalls.c
+++ b/arch/arm64/kvm/hypercalls.c
@@ -44,7 +44,7 @@ static void kvm_ptp_get_time(struct kvm_vcpu *vcpu, u64 *val)
feature = smccc_get_arg1(vcpu);
switch (feature) {
case KVM_PTP_VIRT_COUNTER:
- cycles = systime_snapshot.cycles - vcpu_read_sys_reg(vcpu, CNTVOFF_EL2);
+ cycles = systime_snapshot.cycles - vcpu->kvm->arch.timer_data.voffset;
break;
case KVM_PTP_PHYS_COUNTER:
cycles = systime_snapshot.cycles;
diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h
index 71916de7c6c4..c52a6e6839da 100644
--- a/include/kvm/arm_arch_timer.h
+++ b/include/kvm/arm_arch_timer.h
@@ -23,6 +23,19 @@ enum kvm_arch_timer_regs {
TIMER_REG_CTL,
};
+struct arch_timer_offset {
+ /*
+ * If set, pointer to one of the offsets in the kvm's offset
+ * structure. If NULL, assume a zero offset.
+ */
+ u64 *vm_offset;
+};
+
+struct arch_timer_vm_data {
+ /* Offset applied to the virtual timer/counter */
+ u64 voffset;
+};
+
struct arch_timer_context {
struct kvm_vcpu *vcpu;
@@ -32,6 +45,8 @@ struct arch_timer_context {
/* Emulated Timer (may be unused) */
struct hrtimer hrtimer;
+ /* Offset for this counter/timer */
+ struct arch_timer_offset offset;
/*
* We have multiple paths which can save/restore the timer state onto
* the hardware, so we need some way of keeping track of where the
--
2.34.1
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