linux-kernel - [PATCH 10/18] KVM: x86: Keep track of instruction length during faults

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Message-ID: <20240609154945.55332-11-nsaenz@amazon.com>
Date: Sun, 9 Jun 2024 15:49:39 +0000
From: Nicolas Saenz Julienne <nsaenz@...zon.com>
To: <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>
CC: <pbonzini@...hat.com>, <seanjc@...gle.com>, <vkuznets@...hat.com>,
	<linux-doc@...r.kernel.org>, <linux-hyperv@...r.kernel.org>,
	<linux-arch@...r.kernel.org>, <linux-trace-kernel@...r.kernel.org>,
	<graf@...zon.de>, <dwmw2@...radead.org>, <paul@...zon.com>,
	<nsaenz@...zon.com>, <mlevitsk@...hat.com>, <jgowans@...zon.com>,
	<corbet@....net>, <decui@...rosoft.com>, <tglx@...utronix.de>,
	<mingo@...hat.com>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>,
	<x86@...nel.org>, <amoorthy@...gle.com>
Subject: [PATCH 10/18] KVM: x86: Keep track of instruction length during faults

Both VMX and SVM provide the length of the instruction
being run at the time of the page fault. Save it within 'struct
kvm_page_fault', as it'll become useful in the future.

Signed-off-by: Nicolas Saenz Julienne <nsaenz@...zon.com>
---
 arch/x86/kvm/mmu/mmu.c          | 11 ++++++++---
 arch/x86/kvm/mmu/mmu_internal.h |  5 ++++-
 arch/x86/kvm/vmx/vmx.c          | 16 ++++++++++++++--
 3 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 8d74bdef68c1d..39b113afefdfc 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4271,7 +4271,8 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
 	      work->arch.cr3 != kvm_mmu_get_guest_pgd(vcpu, vcpu->arch.mmu))
 		return;
 
-	kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, work->arch.error_code, true, NULL);
+	kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, work->arch.error_code,
+			      true, NULL, 0);
 }
 
 static inline u8 kvm_max_level_for_order(int order)
@@ -5887,7 +5888,7 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
 
 	if (r == RET_PF_INVALID) {
 		r = kvm_mmu_do_page_fault(vcpu, cr2_or_gpa, error_code, false,
-					  &emulation_type);
+					  &emulation_type, insn_len);
 		if (KVM_BUG_ON(r == RET_PF_INVALID, vcpu->kvm))
 			return -EIO;
 	}
@@ -5924,8 +5925,12 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
 	if (!mmio_info_in_cache(vcpu, cr2_or_gpa, direct) && !is_guest_mode(vcpu))
 		emulation_type |= EMULTYPE_ALLOW_RETRY_PF;
 emulate:
+	/*
+	 * x86_emulate_instruction() expects insn to contain data if
+	 * insn_len > 0.
+	 */
 	return x86_emulate_instruction(vcpu, cr2_or_gpa, emulation_type, insn,
-				       insn_len);
+				       insn ? insn_len : 0);
 }
 EXPORT_SYMBOL_GPL(kvm_mmu_page_fault);
 
diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index ce2fcd19ba6be..a0cde1a0e39b0 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -192,6 +192,7 @@ struct kvm_page_fault {
 	const gpa_t addr;
 	const u64 error_code;
 	const bool prefetch;
+	const u8 insn_len;
 
 	/* Derived from error_code.  */
 	const bool exec;
@@ -288,11 +289,13 @@ static inline void kvm_mmu_prepare_memory_fault_exit(struct kvm_vcpu *vcpu,
 }
 
 static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
-					u64 err, bool prefetch, int *emulation_type)
+					u64 err, bool prefetch,
+					int *emulation_type, u8 insn_len)
 {
 	struct kvm_page_fault fault = {
 		.addr = cr2_or_gpa,
 		.error_code = err,
+		.insn_len = insn_len,
 		.exec = err & PFERR_FETCH_MASK,
 		.write = err & PFERR_WRITE_MASK,
 		.present = err & PFERR_PRESENT_MASK,
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index ac0682fece604..9ba38e0b0c7a8 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5807,11 +5807,13 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
 	if (unlikely(allow_smaller_maxphyaddr && !kvm_vcpu_is_legal_gpa(vcpu, gpa)))
 		return kvm_emulate_instruction(vcpu, 0);
 
-	return kvm_mmu_page_fault(vcpu, gpa, error_code, NULL, 0);
+	return kvm_mmu_page_fault(vcpu, gpa, error_code, NULL,
+				  vmcs_read32(VM_EXIT_INSTRUCTION_LEN));
 }
 
 static int handle_ept_misconfig(struct kvm_vcpu *vcpu)
 {
+	u8 insn_len = 0;
 	gpa_t gpa;
 
 	if (vmx_check_emulate_instruction(vcpu, EMULTYPE_PF, NULL, 0))
@@ -5828,7 +5830,17 @@ static int handle_ept_misconfig(struct kvm_vcpu *vcpu)
 		return kvm_skip_emulated_instruction(vcpu);
 	}
 
-	return kvm_mmu_page_fault(vcpu, gpa, PFERR_RSVD_MASK, NULL, 0);
+	/*
+	 * Using VMCS.VM_EXIT_INSTRUCTION_LEN on EPT misconfig depends on
+	 * undefined behavior: Intel's SDM doesn't mandate the VMCS field be
+	 * set when EPT misconfig occurs.  In practice, real hardware updates
+	 * VM_EXIT_INSTRUCTION_LEN on EPT misconfig, but other hypervisors
+	 * (namely Hyper-V) don't set it due to it being undefined behavior.
+	 */
+	if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
+		insn_len = vmcs_read32(VM_EXIT_INSTRUCTION_LEN);
+
+	return kvm_mmu_page_fault(vcpu, gpa, PFERR_RSVD_MASK, NULL, insn_len);
 }
 
 static int handle_nmi_window(struct kvm_vcpu *vcpu)
-- 
2.40.1