From nobody Sat Jul 25 01:02:36 2026 Received: from smtpbgsg2.qq.com (smtpbgsg2.qq.com [54.254.200.128]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C186D3451DA; Tue, 21 Jul 2026 11:56:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=54.254.200.128 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784634977; cv=none; b=nN5DlTd3H6sv48ghAmMsf7MjuMO6/YbodPSOLoqrBFVPyiR8WjvzedagLK3ypcc6cDjJbVaPn332gAibhUXpaIq06MqEG0wqFez7Rg/xNG2vDx6g1e1iJcPkiziLnXh71VWE68n83bgl5cjnrAxpzcQI8agsFp5/Y6+fjd0yHn4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784634977; c=relaxed/simple; bh=OiKYjHgs8yfl3D/5jJm7sEOb7graCNa31cNxuR7adJM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=i2lEaGdpCd8VfCztZjnWzgoeA9tvr7M37boNPw9dw6mqzYwQu254Bzp+bOVoOpQmTYdMXAURlZwIuQJf18d/51/artyCXTDtOmwl3rq4zz26aqQ9GZJCwlLynL6Vdugu21Ji5YmkX88RU3iZwLVNnL4TW7sLb7p1/+IuZy9oINI= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=haiwei.tech; spf=pass smtp.mailfrom=haiwei.tech; arc=none smtp.client-ip=54.254.200.128 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=haiwei.tech Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=haiwei.tech X-QQ-mid: zesmtpsz6t1784634963t6e8a6e90 X-QQ-Originating-IP: 7UTGWJP3KrvUOqnlyru4WDx7yxHshRvG5L4FHHW3S5o= Received: from rsl ( [183.242.33.186]) by bizesmtp.qq.com (ESMTP) with id ; Tue, 21 Jul 2026 19:56:00 +0800 (CST) X-QQ-SSF: 0000000000000000000000000000000 X-QQ-GoodBg: 0 X-BIZMAIL-ID: 18011628127360508405 EX-QQ-RecipientCnt: 14 From: JinRui To: Anup Patel , Paolo Bonzini , Shuah Khan , Paul Walmsley , Palmer Dabbelt , Albert Ou Cc: Atish Patra , Alexandre Ghiti , kvm@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, jinrui Subject: [PATCH v4] KVM: selftests: riscv: Add lazy V extension enablement for guests Date: Tue, 21 Jul 2026 11:55:58 +0000 Message-ID: <759A31C23819178D+20260721115558.341592-1-jinrui@haiwei.tech> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260721112454.330498-1-jinrui@haiwei.tech> References: <20260721112454.330498-1-jinrui@haiwei.tech> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-QQ-SENDSIZE: 520 Feedback-ID: zesmtpsz:haiwei.tech:qybglogicsvrgz:qybglogicsvrgz6b-0 X-QQ-XMAILINFO: NU1WQlQcW6dRJYxTTHGKZf+WGTLga1Es9GITG2SkkbjAr/a9F3XSzSGY BlIoILboLIoBK1ndhh3Ea1Y5xfQXUcNsuQy6XQvWdBceZl6pRRRz020jYsDyepFEak3vHdu K3ne9iRMRtdYEDi2zvRFuFmyIePydK+zPuOZ+D8V/MdlGnT0CcGVbtyw8yRUVacDJLdcN3x 7xadjVRKOMjd+PX5+Fx+0orK9PFSvScFH1GDAPwfUXBe75N/CGJxsTIDQp20fX+IeI8MkSQ gQZsFf3BOWO+z5KdxnqxhW7H2Bg2TQREnx1QkVrt5k8LdurpwVxPdofC4SdnDLudkdzgPcy j+XB3+PmR5X19BXloxDck4swc1f9J7l3vJQpR0MnEXDK22YEqivfzjB5xMwWkExwTezxk1N 9IViXG8kYEyibsg1wzJ/vz1cFstEOQPL1TMhRtvNa9M3c7OkhkPygeUlIceHAegwy5P/vFy arI8RsmSXXsCT1BSWjfNVbX6l+uAPnwMOimKE4wy2/oE7HZZSBO4VJjv27njVYHVMcUowrw 6YltTD/WcACtCaLfgID2hPk+1oMvJM5Z3ZKShYGPVdXtmXS061QYJHkYKxmatgpC+q8Grjh b6OjQemARTN8C4HCx7t7Ox/LlTWm0hcSQCDjDU3ni9xGZjbL0ZSNhpNfaMJGy84C1R30w9Z bz9XTeu2yaJ7lDlVL6finqZNjuG1cLew4Lavr6otdk5wxId7S4RkG0SxmS86AiOcRTvQX7g 2UrXD7fqtNoTBomuUhr/u/9Rc+fZPas7Qk//KVjOKmQxY4zcHbLjsA9MGFTlAtlNc6ewN8K S1uxuMGnW+ZJSqp0HiGGiGzgplBs5GfB2dFtrZjIQ8kOq7zI9v+MMcdPdDll/SFkUS6pqu4 Wb39DvBDdgolknX2sd7r5B5wvwCmi9L1k81IMPhkx2O/d05pTSUqi2uktL6KEiJwIFpBAw6 qMGUCBTxbDTfXQJ9LYHeRVOC8vHxKzflJNfCREq7EszxUALrnrmufXXh3sImJVJP9b4gkSp s8H6GLHn12RAE0Ks5mNMpgvKFT2KWvm2vU23745SQpo4Y4cU8O6UiloUg4tHX9C4HL0r5S4 pPcn9RFw6J+dQRCGwSxgV8= X-QQ-XMRINFO: Nq+8W0+stu50tPAe92KXseR0ZZmBTk3gLg== X-QQ-RECHKSPAM: 0 Content-Type: text/plain; charset="utf-8" From: jinrui When the cross-compiler defaults to an -march that includes the V (vector) extension, -O2 auto-vectorization generates vector instructions (e.g. vsetvli, vadd.vv) in Guest binary code. If the Guest executes a vector instruction while sstatus.VS is Off, an EXC_INST_ILLEGAL (scause=3D2) is raised. KVM's hedeleg delegates this exception to the Guest, but the selftest has no way to handle it as a bare-metal program, causing all Guest tests to fail. In contrast, a real OS kernel handles this via riscv_v_first_use_handler(), which detects the vector instruction, sets sstatus.VS to Initial, and srets to re-execute. Fix this with four changes in processor.c: 1. Delete the now-unused guest_unexp_trap() handler, which is replaced by the full exception vector table. 2. In vm_arch_vcpu_add(), notify KVM that the Guest is allowed to use the V extension via __vcpu_set_reg(V, 1) (best-effort, silently ignores errors on hardware without V). Also replace the raw stvec handler with the full exception vector table, which provides save_context/restore_context for safe lazy enablement. 3. In route_exception(), add a lazy V enablement check that runs before any test-registered handler. When the cause is a non-IRQ EXC_INST_ILLEGAL and sstatus.VS is Off, set VS to Initial and return so the faulting instruction is re-executed via sret. 4. Make vm_init_vector_tables() idempotent by checking vm->handlers before allocation, so tests that manually call it (ebreak_test, arch_timer, sbi_pmu_test) do not leak memory. The check runs before test-registered EXC_INST_ILLEGAL handlers (e.g. sbi_pmu_test) to ensure V enablement takes priority. Tested on a riscv64 host with KVM enabled: all 12 KVM selftest binaries pass. Signed-off-by: jinrui --- Changes in v4: - Add vcpu_dump() call in assert_on_unhandled_exception() to restore the register dump that was lost when guest_unexp_trap() was removed. Changes in v3: - Move v_available from a host-side static variable into struct handlers (Guest memory), fixing synchronization issue between host (writer) and Guest (reader). Changes in v2: - Add a v_available flag to prevent infinite exception loops on hosts without the V extension. - Use regs->status instead of reading the live sstatus CSR. .../selftests/kvm/lib/riscv/processor.c | 69 ++++++++++++++++--- 1 file changed, 59 insertions(+), 10 deletions(-) diff --git a/tools/testing/selftests/kvm/lib/riscv/processor.c b/tools/test= ing/selftests/kvm/lib/riscv/processor.c index ded5429f3448..bf0675cc86d6 100644 --- a/tools/testing/selftests/kvm/lib/riscv/processor.c +++ b/tools/testing/selftests/kvm/lib/riscv/processor.c @@ -297,14 +297,6 @@ void vcpu_arch_dump(FILE *stream, struct kvm_vcpu *vcp= u, u8 indent) " T3: 0x%016lx T4: 0x%016lx T5: 0x%016lx T6: 0x%016lx\n", core.regs.t3, core.regs.t4, core.regs.t5, core.regs.t6); } - -static void __aligned(16) guest_unexp_trap(void) -{ - sbi_ecall(KVM_RISCV_SELFTESTS_SBI_EXT, - KVM_RISCV_SELFTESTS_SBI_UNEXP, - 0, 0, 0, 0, 0, 0); -} - void vcpu_arch_set_entry_point(struct kvm_vcpu *vcpu, void *guest_code) { vcpu_set_reg(vcpu, RISCV_CORE_REG(regs.pc), (unsigned long)guest_code); @@ -348,8 +340,33 @@ struct kvm_vcpu *vm_arch_vcpu_add(struct kvm_vm *vm, u= 32 vcpu_id) /* Setup sscratch for guest_get_vcpuid() */ vcpu_set_reg(vcpu, RISCV_GENERAL_CSR_REG(sscratch), vcpu_id); =20 - /* Setup default exception vector of guest */ - vcpu_set_reg(vcpu, RISCV_GENERAL_CSR_REG(stvec), (unsigned long)guest_une= xp_trap); + /* + * Enable the V (vector) extension in KVM so that the compiler can + * safely generate vector instructions (e.g. via -O2 auto- + * vectorization). Silently ignore errors; the test will still work + * without V. + */ + __vcpu_set_reg(vcpu, RISCV_ISA_EXT_REG(KVM_RISCV_ISA_EXT_V), 1); + + /* + * Use the full exception vector table (which provides lazy V + * extension enablement for EXC_INST_ILLEGAL in route_exception) + * as the default exception handler. vm_init_vector_tables() is + * idempotent; tests that call it again will get a no-op. + */ + vm_init_vector_tables(vm); + vcpu_init_vector_tables(vcpu); + + /* + * Record V extension availability in the handlers struct so that + * route_exception() (called from Guest context) can check it + * without relying on a host-side global variable. + */ + { + struct handlers *h =3D addr_gva2hva(vm, vm->handlers); + + h->v_available =3D __vcpu_has_isa_ext(vcpu, KVM_RISCV_ISA_EXT_V); + } =20 return vcpu; } @@ -408,6 +425,7 @@ void assert_on_unhandled_exception(struct kvm_vcpu *vcp= u) struct ucall uc; =20 if (get_ucall(vcpu, &uc) =3D=3D UCALL_UNHANDLED) { + vcpu_dump(stderr, vcpu, 2); TEST_FAIL("Unexpected exception (vector:0x%lx, ec:0x%lx)", uc.args[0], uc.args[1]); } @@ -415,6 +433,7 @@ void assert_on_unhandled_exception(struct kvm_vcpu *vcp= u) =20 struct handlers { exception_handler_fn exception_handlers[NR_VECTORS][NR_EXCEPTIONS]; + bool v_available; }; =20 void route_exception(struct pt_regs *regs) @@ -432,6 +451,33 @@ void route_exception(struct pt_regs *regs) ec =3D 0; } =20 + /* + * Handle V (vector) extension lazy enablement before any + * registered handler. The compiler's default march may include + * V, and auto-vectorization generates vector instructions that + * trigger EXC_INST_ILLEGAL when VS (Vector Status) in sstatus + * is Off. Enable VS to Initial and re-execute the faulting + * instruction, mimicking what a real OS kernel does. + * + * This check runs before any test-registered handler, so tests + * that install their own EXC_INST_ILLEGAL handler (e.g. + * sbi_pmu_test) are not affected. + */ + if (!(regs->cause & CAUSE_IRQ_FLAG) && ec =3D=3D EXC_INST_ILLEGAL) { + /* + * If KVM supports the V extension for this Guest and VS + * (Vector Status) is Off in the saved sstatus, set it to + * Initial and sret to re-execute the faulting instruction. + * Use regs->status (saved at exception entry) rather than + * reading the live CSR to avoid a TOCTOU race with nested + * exceptions. + */ + if (handlers && handlers->v_available && !(regs->status & SR_VS)) { + regs->status |=3D SR_VS_INITIAL; + return; + } + } + if (handlers && handlers->exception_handlers[vector][ec]) return handlers->exception_handlers[vector][ec](regs); =20 @@ -448,6 +494,9 @@ void vcpu_init_vector_tables(struct kvm_vcpu *vcpu) =20 void vm_init_vector_tables(struct kvm_vm *vm) { + if (vm->handlers) + return; + vm->handlers =3D __vm_alloc(vm, sizeof(struct handlers), vm->page_size, MEM_REGION_DATA); =20 --=20 2.43.0