RISC-V: KVM: Fix kvm_riscv_vcpu_timer_pending() for Sstc

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: 8f5cb44b ("RISC-V: KVM: Support sstc extension")
Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Anup Patel <anup@brainfault.org>

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);
 

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)

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;