Hi Marc, On Fri, Feb 24, 2023 at 07:16:40PM +0000, Marc Zyngier wrote: > 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@xxxxxxx> > Reviewed-by: Reiji Watanabe <reijiw@xxxxxxxxxx> > Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx> > Link: https://lore.kernel.org/r/20230224173915.GA17407@xxxxxxxxxxxxxxxxxxxxxxxxx Fixes my mismatched timer offset issues. Tested-by: Joey Gouly <joey.gouly@xxxxxxx> Thanks, Joey > --- > 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
