[PATCH] RISC-V: KVM: Fix kvm_riscv_vcpu_timer_pending() for Sstc

From: Anup Patel
Date: Wed Oct 19 2022 - 08:11:50 EST


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