On Wed, Oct 19, 2022 at 4:45 AM Anup Patel <apatel@xxxxxxxxxxxxxxxx> wrote:
>
> The kvm_riscv_vcpu_timer_pending() checks per-VCPU next_cycles
> and per-VCPU software injected VS timer interrupt. This function
> returns incorrect value when Sstc is available because the per-VCPU
> next_cycles are only updated by kvm_riscv_vcpu_timer_save() called
> from kvm_arch_vcpu_put(). As a result, when Sstc is available the
> VCPU does not block properly upon WFI traps.
>
> To fix the above issue, we introduce kvm_riscv_vcpu_timer_sync()
> which will update per-VCPU next_cycles upon every VM exit instead
> of kvm_riscv_vcpu_timer_save().
>
> Fixes: 8f5cb44b1bae ("RISC-V: KVM: Support sstc extension")
> Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
> ---
> arch/riscv/include/asm/kvm_vcpu_timer.h | 1 +
> arch/riscv/kvm/vcpu.c | 3 +++
> arch/riscv/kvm/vcpu_timer.c | 17 +++++++++++++++--
> 3 files changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/include/asm/kvm_vcpu_timer.h b/arch/riscv/include/asm/kvm_vcpu_timer.h
> index 0d8fdb8ec63a..82f7260301da 100644
> --- a/arch/riscv/include/asm/kvm_vcpu_timer.h
> +++ b/arch/riscv/include/asm/kvm_vcpu_timer.h
> @@ -45,6 +45,7 @@ int kvm_riscv_vcpu_timer_deinit(struct kvm_vcpu *vcpu);
> int kvm_riscv_vcpu_timer_reset(struct kvm_vcpu *vcpu);
> void kvm_riscv_vcpu_timer_restore(struct kvm_vcpu *vcpu);
> void kvm_riscv_guest_timer_init(struct kvm *kvm);
> +void kvm_riscv_vcpu_timer_sync(struct kvm_vcpu *vcpu);
> void kvm_riscv_vcpu_timer_save(struct kvm_vcpu *vcpu);
> bool kvm_riscv_vcpu_timer_pending(struct kvm_vcpu *vcpu);
>
> diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> index a032c4f0d600..71ebbc4821f0 100644
> --- a/arch/riscv/kvm/vcpu.c
> +++ b/arch/riscv/kvm/vcpu.c
> @@ -708,6 +708,9 @@ void kvm_riscv_vcpu_sync_interrupts(struct kvm_vcpu *vcpu)
> clear_bit(IRQ_VS_SOFT, &v->irqs_pending);
> }
> }
> +
> + /* Sync-up timer CSRs */
> + kvm_riscv_vcpu_timer_sync(vcpu);
> }
>
> int kvm_riscv_vcpu_set_interrupt(struct kvm_vcpu *vcpu, unsigned int irq)
> diff --git a/arch/riscv/kvm/vcpu_timer.c b/arch/riscv/kvm/vcpu_timer.c
> index 185f2386a747..ad34519c8a13 100644
> --- a/arch/riscv/kvm/vcpu_timer.c
> +++ b/arch/riscv/kvm/vcpu_timer.c
> @@ -320,20 +320,33 @@ void kvm_riscv_vcpu_timer_restore(struct kvm_vcpu *vcpu)
> kvm_riscv_vcpu_timer_unblocking(vcpu);
> }
>
> -void kvm_riscv_vcpu_timer_save(struct kvm_vcpu *vcpu)
> +void kvm_riscv_vcpu_timer_sync(struct kvm_vcpu *vcpu)
> {
> struct kvm_vcpu_timer *t = &vcpu->arch.timer;
>
> if (!t->sstc_enabled)
> return;
>
> - t = &vcpu->arch.timer;
> #if defined(CONFIG_32BIT)
> t->next_cycles = csr_read(CSR_VSTIMECMP);
> t->next_cycles |= (u64)csr_read(CSR_VSTIMECMPH) << 32;
> #else
> t->next_cycles = csr_read(CSR_VSTIMECMP);
> #endif
> +}
> +
> +void kvm_riscv_vcpu_timer_save(struct kvm_vcpu *vcpu)
> +{
> + struct kvm_vcpu_timer *t = &vcpu->arch.timer;
> +
> + if (!t->sstc_enabled)
> + return;
> +
> + /*
> + * The vstimecmp CSRs are saved by kvm_riscv_vcpu_timer_sync()
> + * upon every VM exit so no need to save here.
> + */
> +
> /* timer should be enabled for the remaining operations */
> if (unlikely(!t->init_done))
> return;
> --
> 2.34.1
>
Ahh. That's a tricky one. Thanks for fixing it.
Reviewed-by: Atish Patra <atishp@xxxxxxxxxxxx>
--
Regards,
Atish
