linux-kernel - [PATCH v2] RISC-V: KVM: Delegate kvm unhandled faults to VS mode

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Message-Id: <20250710133030.88940-1-luxu.kernel@bytedance.com>
Date: Thu, 10 Jul 2025 21:30:30 +0800
From: Xu Lu <luxu.kernel@...edance.com>
To: rkrcmar@...tanamicro.com,
	cleger@...osinc.com,
	anup@...infault.org,
	atish.patra@...ux.dev,
	paul.walmsley@...ive.com,
	palmer@...belt.com,
	aou@...s.berkeley.edu,
	alex@...ti.fr
Cc: kvm@...r.kernel.org,
	kvm-riscv@...ts.infradead.org,
	linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Xu Lu <luxu.kernel@...edance.com>
Subject: [PATCH v2] RISC-V: KVM: Delegate kvm unhandled faults to VS mode

Delegate faults which are not handled by kvm to VS mode to avoid
unnecessary traps to HS mode. These faults include illegal instruction
fault, instruction access fault, load access fault and store access
fault.

The delegation of illegal instruction fault is particularly important
to guest applications that use vector instructions frequently. In such
cases, an illegal instruction fault will be raised when guest user thread
uses vector instruction the first time and then guest kernel will enable
user thread to execute following vector instructions.

The fw pmu event counters remain undeleted so that guest can still get
these events via sbi call. Guest will only see zero count on these
events and know 'firmware' has delegated these faults.

Signed-off-by: Xu Lu <luxu.kernel@...edance.com>
---
 arch/riscv/include/asm/kvm_host.h |  4 ++++
 arch/riscv/kvm/vcpu_exit.c        | 18 ------------------
 2 files changed, 4 insertions(+), 18 deletions(-)

diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
index 85cfebc32e4cf..e04851cf0115c 100644
--- a/arch/riscv/include/asm/kvm_host.h
+++ b/arch/riscv/include/asm/kvm_host.h
@@ -44,7 +44,11 @@
 #define KVM_REQ_STEAL_UPDATE		KVM_ARCH_REQ(6)
 
 #define KVM_HEDELEG_DEFAULT		(BIT(EXC_INST_MISALIGNED) | \
+					 BIT(EXC_INST_ACCESS)     | \
+					 BIT(EXC_INST_ILLEGAL)    | \
 					 BIT(EXC_BREAKPOINT)      | \
+					 BIT(EXC_LOAD_ACCESS)     | \
+					 BIT(EXC_STORE_ACCESS)    | \
 					 BIT(EXC_SYSCALL)         | \
 					 BIT(EXC_INST_PAGE_FAULT) | \
 					 BIT(EXC_LOAD_PAGE_FAULT) | \
diff --git a/arch/riscv/kvm/vcpu_exit.c b/arch/riscv/kvm/vcpu_exit.c
index 6e0c184127956..6e2302c65e193 100644
--- a/arch/riscv/kvm/vcpu_exit.c
+++ b/arch/riscv/kvm/vcpu_exit.c
@@ -193,11 +193,6 @@ int kvm_riscv_vcpu_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
 	ret = -EFAULT;
 	run->exit_reason = KVM_EXIT_UNKNOWN;
 	switch (trap->scause) {
-	case EXC_INST_ILLEGAL:
-		kvm_riscv_vcpu_pmu_incr_fw(vcpu, SBI_PMU_FW_ILLEGAL_INSN);
-		vcpu->stat.instr_illegal_exits++;
-		ret = vcpu_redirect(vcpu, trap);
-		break;
 	case EXC_LOAD_MISALIGNED:
 		kvm_riscv_vcpu_pmu_incr_fw(vcpu, SBI_PMU_FW_MISALIGNED_LOAD);
 		vcpu->stat.load_misaligned_exits++;
@@ -208,19 +203,6 @@ int kvm_riscv_vcpu_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
 		vcpu->stat.store_misaligned_exits++;
 		ret = vcpu_redirect(vcpu, trap);
 		break;
-	case EXC_LOAD_ACCESS:
-		kvm_riscv_vcpu_pmu_incr_fw(vcpu, SBI_PMU_FW_ACCESS_LOAD);
-		vcpu->stat.load_access_exits++;
-		ret = vcpu_redirect(vcpu, trap);
-		break;
-	case EXC_STORE_ACCESS:
-		kvm_riscv_vcpu_pmu_incr_fw(vcpu, SBI_PMU_FW_ACCESS_STORE);
-		vcpu->stat.store_access_exits++;
-		ret = vcpu_redirect(vcpu, trap);
-		break;
-	case EXC_INST_ACCESS:
-		ret = vcpu_redirect(vcpu, trap);
-		break;
 	case EXC_VIRTUAL_INST_FAULT:
 		if (vcpu->arch.guest_context.hstatus & HSTATUS_SPV)
 			ret = kvm_riscv_vcpu_virtual_insn(vcpu, run, trap);
-- 
2.20.1