Commit 47053904 authored by Marc Zyngier's avatar Marc Zyngier Committed by Oliver Upton
Browse files

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: default avatarJoey Gouly <joey.gouly@arm.com>
Reviewed-by: default avatarReiji Watanabe <reijiw@google.com>
Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230224173915.GA17407@e124191.cambridge.arm.com


Tested-by: default avatarJoey Gouly <joey.gouly@arm.com>
Link: https://lore.kernel.org/r/20230224191640.3396734-1-maz@kernel.org


Signed-off-by: default avatarOliver Upton <oliver.upton@linux.dev>
parent fe15c26e

arch/arm64/include/asm/kvm_host.h

+3 −0
Original line number Diff line number Diff line
@@ -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;

arch/arm64/kvm/arch_timer.c

+10 −35
Original line number Diff line number Diff line
@@ -84,15 +84,11 @@ 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;

}

}



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);

arch/arm64/kvm/hypercalls.c

+1 −1
Original line number Diff line number Diff line
@@ -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;

include/kvm/arm_arch_timer.h

+15 −0
Original line number Diff line number Diff line
@@ -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