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Thu, 06 Nov 2025 21:29:52 +0800 From: fangyu.yu@linux.alibaba.com To: anup@brainfault.org Cc: alex@ghiti.fr, aou@eecs.berkeley.edu, atish.patra@linux.dev, fangyu.yu@linux.alibaba.com, graf@amazon.com, guoren@kernel.org, jiangyifei@huawei.com, kvm-riscv@lists.infradead.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, palmer@dabbelt.com, paul.walmsley@sifive.com, pbonzini@redhat.com Subject: Re: Re: [PATCH] RISC-V: KVM: Fix guest page fault within HLV* instructions Date: Thu, 6 Nov 2025 21:29:50 +0800 Message-Id: <20251106132950.80534-1-fangyu.yu@linux.alibaba.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit >> From: Fangyu Yu >> >> 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 >> --- >> 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; > >This looks like an unrelated change so drop it or send a separate patch >with proper explanation. > >> + case EXC_LOAD_GUEST_PAGE_FAULT: >> + return KVM_INSN_CONTINUE_SAME_SEPC; > >The KVM_INSN_xyz enum values are only for functions called via >system_opcode_insn() so return 1 over here just like the below >default case. > >Also, add some comments over here about why we are simply >continuing the guest. > >> + 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; > >This looks like an unrelated change so drop it or send a separate patch >with proper explanation. > >> + case EXC_LOAD_GUEST_PAGE_FAULT: >> + return KVM_INSN_CONTINUE_SAME_SEPC; > >Same comment as kvm_riscv_vcpu_virtual_insn(). > >> + 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; > >This looks like an unrelated change so drop it or send a separate patch >with proper explanation. > >> + case EXC_LOAD_GUEST_PAGE_FAULT: >> + return KVM_INSN_CONTINUE_SAME_SEPC; > >Same comment as kvm_riscv_vcpu_virtual_insn(). > >> + default: >> /* Redirect trap if we failed to read instruction */ >> utrap.sepc = ct->sepc; >> kvm_riscv_vcpu_trap_redirect(vcpu, &utrap); >> -- >> 2.49.0 >> >> > >Regards, >Anup Hi Anup: Thanks for the review. I will follow your suggestions in the next version. Thanks, Fangyu