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KVM: arm64: timers: Convert per-vcpu virtual offset to a global value 

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@arm.com>
Reviewed-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230224173915.GA17407@e124191.cambridge.arm.com
Tested-by: Joey Gouly <joey.gouly@arm.com>
Link: https://lore.kernel.org/r/20230224191640.3396734-1-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
This commit is contained in:
Marc Zyngier 2023-02-24 19:16:40 +00:00 committed by Oliver Upton
parent fe15c26ee2
commit 47053904e1
4 changed files with 29 additions and 36 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
arch/arm64/include/asm/kvm_host.h
View File

@ -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;

45
arch/arm64/kvm/arch_timer.c
View File

@ -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);

2
arch/arm64/kvm/hypercalls.c
View File

@ -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;

15
include/kvm/arm_arch_timer.h
View File

@ -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