* [PATCH v2] RISC-V: KVM: Fix guest page fault within HLV* instructions
@ 2025-11-11 13:55 fangyu.yu
2025-11-12 19:41 ` Andrew Jones
0 siblings, 1 reply; 3+ messages in thread
From: fangyu.yu @ 2025-11-11 13:55 UTC (permalink / raw)
To: anup, atish.patra, pjw, palmer, aou, alex
Cc: guoren, kvm, kvm-riscv, linux-riscv, linux-kernel, Fangyu Yu
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: b91f0e4cb8a3 ("RISC-V: KVM: Factor-out instruction emulation into separate sources")
Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
---
Changes in v2:
- Remove unnecessary modifications and add comments(suggested by Anup)
- Update Fixes tag
- Link to v1: https://lore.kernel.org/linux-riscv/20250912134332.22053-1-fangyu.yu@linux.alibaba.com/
---
arch/riscv/kvm/vcpu_insn.c | 39 ++++++++++++++++++++++++++++++++++++++
1 file changed, 39 insertions(+)
diff --git a/arch/riscv/kvm/vcpu_insn.c b/arch/riscv/kvm/vcpu_insn.c
index de1f96ea6225..a8d796ef2822 100644
--- a/arch/riscv/kvm/vcpu_insn.c
+++ b/arch/riscv/kvm/vcpu_insn.c
@@ -323,6 +323,19 @@ int kvm_riscv_vcpu_virtual_insn(struct kvm_vcpu *vcpu, struct kvm_run *run,
ct->sepc,
&utrap);
if (utrap.scause) {
+ /**
+ * If a g-stage page fault occurs, the direct approach
+ * is to let the g-stage page fault handler handle it
+ * naturally, however, calling the g-stage page fault
+ * handler here seems rather strange.
+ * Considering this is an corner case, we can directly
+ * return to the guest and re-execute the same PC, this
+ * will trigger a g-stage page fault again and then the
+ * regular g-stage page fault handler will populate
+ * g-stage page table.
+ */
+ if (utrap.scause == EXC_LOAD_GUEST_PAGE_FAULT)
+ return 1;
utrap.sepc = ct->sepc;
kvm_riscv_vcpu_trap_redirect(vcpu, &utrap);
return 1;
@@ -378,6 +391,19 @@ 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) {
+ /**
+ * If a g-stage page fault occurs, the direct approach
+ * is to let the g-stage page fault handler handle it
+ * naturally, however, calling the g-stage page fault
+ * handler here seems rather strange.
+ * Considering this is an corner case, we can directly
+ * return to the guest and re-execute the same PC, this
+ * will trigger a g-stage page fault again and then the
+ * regular g-stage page fault handler will populate
+ * g-stage page table.
+ */
+ if (utrap.scause == EXC_LOAD_GUEST_PAGE_FAULT)
+ return 1;
/* Redirect trap if we failed to read instruction */
utrap.sepc = ct->sepc;
kvm_riscv_vcpu_trap_redirect(vcpu, &utrap);
@@ -504,6 +530,19 @@ 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) {
+ /**
+ * If a g-stage page fault occurs, the direct approach
+ * is to let the g-stage page fault handler handle it
+ * naturally, however, calling the g-stage page fault
+ * handler here seems rather strange.
+ * Considering this is an corner case, we can directly
+ * return to the guest and re-execute the same PC, this
+ * will trigger a g-stage page fault again and then the
+ * regular g-stage page fault handler will populate
+ * g-stage page table.
+ */
+ if (utrap.scause == EXC_LOAD_GUEST_PAGE_FAULT)
+ return 1;
/* Redirect trap if we failed to read instruction */
utrap.sepc = ct->sepc;
kvm_riscv_vcpu_trap_redirect(vcpu, &utrap);
--
2.50.1
--
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http://lists.infradead.org/mailman/listinfo/kvm-riscv
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH v2] RISC-V: KVM: Fix guest page fault within HLV* instructions
2025-11-11 13:55 [PATCH v2] RISC-V: KVM: Fix guest page fault within HLV* instructions fangyu.yu
@ 2025-11-12 19:41 ` Andrew Jones
2025-11-14 0:38 ` fangyu.yu
0 siblings, 1 reply; 3+ messages in thread
From: Andrew Jones @ 2025-11-12 19:41 UTC (permalink / raw)
To: fangyu.yu
Cc: anup, atish.patra, pjw, palmer, aou, alex, guoren, kvm, kvm-riscv,
linux-riscv, linux-kernel
On Tue, Nov 11, 2025 at 09:55:06PM +0800, fangyu.yu@linux.alibaba.com wrote:
> 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: b91f0e4cb8a3 ("RISC-V: KVM: Factor-out instruction emulation into separate sources")
> Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
>
> ---
> Changes in v2:
> - Remove unnecessary modifications and add comments(suggested by Anup)
> - Update Fixes tag
> - Link to v1: https://lore.kernel.org/linux-riscv/20250912134332.22053-1-fangyu.yu@linux.alibaba.com/
> ---
> arch/riscv/kvm/vcpu_insn.c | 39 ++++++++++++++++++++++++++++++++++++++
> 1 file changed, 39 insertions(+)
>
> diff --git a/arch/riscv/kvm/vcpu_insn.c b/arch/riscv/kvm/vcpu_insn.c
> index de1f96ea6225..a8d796ef2822 100644
> --- a/arch/riscv/kvm/vcpu_insn.c
> +++ b/arch/riscv/kvm/vcpu_insn.c
> @@ -323,6 +323,19 @@ int kvm_riscv_vcpu_virtual_insn(struct kvm_vcpu *vcpu, struct kvm_run *run,
> ct->sepc,
> &utrap);
> if (utrap.scause) {
> + /**
> + * If a g-stage page fault occurs, the direct approach
> + * is to let the g-stage page fault handler handle it
> + * naturally, however, calling the g-stage page fault
> + * handler here seems rather strange.
> + * Considering this is an corner case, we can directly
> + * return to the guest and re-execute the same PC, this
> + * will trigger a g-stage page fault again and then the
> + * regular g-stage page fault handler will populate
> + * g-stage page table.
> + */
> + if (utrap.scause == EXC_LOAD_GUEST_PAGE_FAULT)
> + return 1;
> utrap.sepc = ct->sepc;
> kvm_riscv_vcpu_trap_redirect(vcpu, &utrap);
> return 1;
> @@ -378,6 +391,19 @@ 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) {
> + /**
> + * If a g-stage page fault occurs, the direct approach
> + * is to let the g-stage page fault handler handle it
> + * naturally, however, calling the g-stage page fault
> + * handler here seems rather strange.
> + * Considering this is an corner case, we can directly
> + * return to the guest and re-execute the same PC, this
> + * will trigger a g-stage page fault again and then the
> + * regular g-stage page fault handler will populate
> + * g-stage page table.
> + */
> + if (utrap.scause == EXC_LOAD_GUEST_PAGE_FAULT)
> + return 1;
> /* Redirect trap if we failed to read instruction */
> utrap.sepc = ct->sepc;
> kvm_riscv_vcpu_trap_redirect(vcpu, &utrap);
> @@ -504,6 +530,19 @@ 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) {
> + /**
> + * If a g-stage page fault occurs, the direct approach
> + * is to let the g-stage page fault handler handle it
> + * naturally, however, calling the g-stage page fault
> + * handler here seems rather strange.
> + * Considering this is an corner case, we can directly
> + * return to the guest and re-execute the same PC, this
> + * will trigger a g-stage page fault again and then the
> + * regular g-stage page fault handler will populate
> + * g-stage page table.
> + */
> + if (utrap.scause == EXC_LOAD_GUEST_PAGE_FAULT)
> + return 1;
> /* Redirect trap if we failed to read instruction */
> utrap.sepc = ct->sepc;
> kvm_riscv_vcpu_trap_redirect(vcpu, &utrap);
> --
> 2.50.1
>
To avoid repeating the same paragraph three times I would create a
helper function, kvm_riscv_check_load_guest_page_fault(), with the
paragraph placed in that function along with the utrap.scause
exception type check.
Thanks,
drew
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^ permalink raw reply [flat|nested] 3+ messages in thread* Re: Re: [PATCH v2] RISC-V: KVM: Fix guest page fault within HLV* instructions
2025-11-12 19:41 ` Andrew Jones
@ 2025-11-14 0:38 ` fangyu.yu
0 siblings, 0 replies; 3+ messages in thread
From: fangyu.yu @ 2025-11-14 0:38 UTC (permalink / raw)
To: ajones
Cc: alex, anup, aou, atish.patra, fangyu.yu, guoren, kvm-riscv, kvm,
linux-kernel, linux-riscv, palmer, pjw
>> 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: b91f0e4cb8a3 ("RISC-V: KVM: Factor-out instruction emulation into separate sources")
>> Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
>>
>> ---
>> Changes in v2:
>> - Remove unnecessary modifications and add comments(suggested by Anup)
>> - Update Fixes tag
>> - Link to v1: https://lore.kernel.org/linux-riscv/20250912134332.22053-1-fangyu.yu@linux.alibaba.com/
>> ---
>> arch/riscv/kvm/vcpu_insn.c | 39 ++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 39 insertions(+)
>>
>> diff --git a/arch/riscv/kvm/vcpu_insn.c b/arch/riscv/kvm/vcpu_insn.c
>> index de1f96ea6225..a8d796ef2822 100644
>> --- a/arch/riscv/kvm/vcpu_insn.c
>> +++ b/arch/riscv/kvm/vcpu_insn.c
>> @@ -323,6 +323,19 @@ int kvm_riscv_vcpu_virtual_insn(struct kvm_vcpu *vcpu, struct kvm_run *run,
>> ct->sepc,
>> &utrap);
>> if (utrap.scause) {
>> + /**
>> + * If a g-stage page fault occurs, the direct approach
>> + * is to let the g-stage page fault handler handle it
>> + * naturally, however, calling the g-stage page fault
>> + * handler here seems rather strange.
>> + * Considering this is an corner case, we can directly
>> + * return to the guest and re-execute the same PC, this
>> + * will trigger a g-stage page fault again and then the
>> + * regular g-stage page fault handler will populate
>> + * g-stage page table.
>> + */
>> + if (utrap.scause == EXC_LOAD_GUEST_PAGE_FAULT)
>> + return 1;
>> utrap.sepc = ct->sepc;
>> kvm_riscv_vcpu_trap_redirect(vcpu, &utrap);
>> return 1;
>> @@ -378,6 +391,19 @@ 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) {
>> + /**
>> + * If a g-stage page fault occurs, the direct approach
>> + * is to let the g-stage page fault handler handle it
>> + * naturally, however, calling the g-stage page fault
>> + * handler here seems rather strange.
>> + * Considering this is an corner case, we can directly
>> + * return to the guest and re-execute the same PC, this
>> + * will trigger a g-stage page fault again and then the
>> + * regular g-stage page fault handler will populate
>> + * g-stage page table.
>> + */
>> + if (utrap.scause == EXC_LOAD_GUEST_PAGE_FAULT)
>> + return 1;
>> /* Redirect trap if we failed to read instruction */
>> utrap.sepc = ct->sepc;
>> kvm_riscv_vcpu_trap_redirect(vcpu, &utrap);
>> @@ -504,6 +530,19 @@ 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) {
>> + /**
>> + * If a g-stage page fault occurs, the direct approach
>> + * is to let the g-stage page fault handler handle it
>> + * naturally, however, calling the g-stage page fault
>> + * handler here seems rather strange.
>> + * Considering this is an corner case, we can directly
>> + * return to the guest and re-execute the same PC, this
>> + * will trigger a g-stage page fault again and then the
>> + * regular g-stage page fault handler will populate
>> + * g-stage page table.
>> + */
>> + if (utrap.scause == EXC_LOAD_GUEST_PAGE_FAULT)
>> + return 1;
>> /* Redirect trap if we failed to read instruction */
>> utrap.sepc = ct->sepc;
>> kvm_riscv_vcpu_trap_redirect(vcpu, &utrap);
>> --
>> 2.50.1
>>
>
>To avoid repeating the same paragraph three times I would create a
>helper function, kvm_riscv_check_load_guest_page_fault(), with the
>paragraph placed in that function along with the utrap.scause
>exception type check.
>
>Thanks,
>drew
Thanks for the suggestion! I'll incorporate this change in the next version.
Thanks,
Fangyu
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2025-11-11 13:55 [PATCH v2] RISC-V: KVM: Fix guest page fault within HLV* instructions fangyu.yu
2025-11-12 19:41 ` Andrew Jones
2025-11-14 0:38 ` fangyu.yu
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