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

fangyu.yu@linux.alibaba.com posted 1 patch 2 weeks, 6 days ago 
arch/riscv/kvm/vcpu_insn.c | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)
[PATCH] RISC-V: KVM: Fix guest page fault within HLV* instructions
Posted by fangyu.yu@linux.alibaba.com 2 weeks, 6 days ago 
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
[PATCH] RISC-V: KVM: Fix guest page fault within HLV* instructions
Posted by fangyu.yu@linux.alibaba.com 2 weeks, 6 days ago 
>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
Re: [PATCH] RISC-V: KVM: Fix guest page fault within HLV* instructions
Posted by fangyu.yu@linux.alibaba.com 2 weeks, 5 days ago 
>>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.

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
>

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