[PATCH] RISC-V: KVM: Fix guest page fault within HLV* instructions

[fangyu.yu@linux.alibaba.com]

>From: Fangyu Yu <fangyu.yu@linux.alibaba.com>
>
>When executing HLV* instructions at the HS mode, a guest page fault
>may occur when a g-stage page table migration between triggering the
>virtual instruction exception and executing the HLV* instruction.
>
>This may be a corner case, and one simpler way to handle this is to
>re-execute the instruction where the virtual  instruction exception
>occurred, and the guest page fault will be automatically handled.
>
>Fixes: 9f7013265112 ("RISC-V: KVM: Handle MMIO exits for VCPU")
>Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
>---
> arch/riscv/kvm/vcpu_insn.c | 21 ++++++++++++++++++---
> 1 file changed, 18 insertions(+), 3 deletions(-)
>
>diff --git a/arch/riscv/kvm/vcpu_insn.c b/arch/riscv/kvm/vcpu_insn.c
>index 97dec18e6989..a8b93aa4d8ec 100644
>--- a/arch/riscv/kvm/vcpu_insn.c
>+++ b/arch/riscv/kvm/vcpu_insn.c
>@@ -448,7 +448,12 @@ int kvm_riscv_vcpu_virtual_insn(struct kvm_vcpu *vcpu, struct kvm_run *run,
> 			insn = kvm_riscv_vcpu_unpriv_read(vcpu, true,
> 							  ct->sepc,
> 							  &utrap);
>-			if (utrap.scause) {
>+			switch (utrap.scause) {
>+			case 0:
>+				break;
>+			case EXC_LOAD_GUEST_PAGE_FAULT:
>+				return KVM_INSN_CONTINUE_SAME_SEPC;
>+			default:
> 				utrap.sepc = ct->sepc;
> 				kvm_riscv_vcpu_trap_redirect(vcpu, &utrap);
> 				return 1;
>@@ -503,7 +508,12 @@ int kvm_riscv_vcpu_mmio_load(struct kvm_vcpu *vcpu, struct kvm_run *run,
> 		 */
> 		insn = kvm_riscv_vcpu_unpriv_read(vcpu, true, ct->sepc,
> 						  &utrap);
>-		if (utrap.scause) {
>+		switch (utrap.scause) {
>+		case 0:
>+			break;
>+		case EXC_LOAD_GUEST_PAGE_FAULT:
>+			return KVM_INSN_CONTINUE_SAME_SEPC;
>+		default:
> 			/* Redirect trap if we failed to read instruction */
> 			utrap.sepc = ct->sepc;
> 			kvm_riscv_vcpu_trap_redirect(vcpu, &utrap);
>@@ -629,7 +639,12 @@ int kvm_riscv_vcpu_mmio_store(struct kvm_vcpu *vcpu, struct kvm_run *run,
> 		 */
> 		insn = kvm_riscv_vcpu_unpriv_read(vcpu, true, ct->sepc,
> 						  &utrap);
>-		if (utrap.scause) {
>+		switch (utrap.scause) {
>+		case 0:
>+			break;
>+		case EXC_LOAD_GUEST_PAGE_FAULT:

Here should be EXC_STORE_GUEST_PAGE_FAULT, I will fix it next version.

>+			return KVM_INSN_CONTINUE_SAME_SEPC;
>+		default:
> 			/* Redirect trap if we failed to read instruction */
> 			utrap.sepc = ct->sepc;
> 			kvm_riscv_vcpu_trap_redirect(vcpu, &utrap);
>-- 
>2.49.0

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