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

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Message-Id: <20250913012451.33829-1-fangyu.yu@linux.alibaba.com>
Date: Sat, 13 Sep 2025 09:24:51 +0800
From: fangyu.yu@...ux.alibaba.com
To: fangyu.yu@...ux.alibaba.com
Cc: alex@...ti.fr,
	anup@...infault.org,
	aou@...s.berkeley.edu,
	atish.patra@...ux.dev,
	graf@...zon.com,
	guoren@...nel.org,
	jiangyifei@...wei.com,
	kvm-riscv@...ts.infradead.org,
	kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org,
	palmer@...belt.com,
	paul.walmsley@...ive.com,
	pbonzini@...hat.com
Subject: Re: [PATCH] RISC-V: KVM: Fix guest page fault within HLV* instructions

>>From: Fangyu Yu <fangyu.yu@...ux.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@...ux.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.

Please ignore this comment, EXC_LOAD_GUEST_PAGE_FAULT is correct.

>
>>+			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
>