[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:
+			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