linux-kernel - Re: [PATCH] KVM: VMX: Report up-to-date exit qualification to userspace

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Message-ID: <ZcOqEBTJ5espqX0E@google.com>
Date: Wed, 7 Feb 2024 08:04:32 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Chao Gao <chao.gao@...el.com>
Cc: kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: VMX: Report up-to-date exit qualification to userspace

On Fri, Dec 29, 2023, Chao Gao wrote:
> Use vmx_get_exit_qual() to read the exit qualification.
> 
> vcpu->arch.exit_qualification is cached for EPT violation only and even
> for EPT violation, it is stale at this point because the up-to-date
> value is cached later in handle_ept_violation().

Oof, vcpu->arch.exit_qualification is *gross*.  At a glance, it should be
straightforward to get rid of it and use the fault structure to pass the info
that comes from the MMU.  I'll post a patch, assuming it works.

As for this patch, I'll get it applied for 6.9.

---
 arch/x86/include/asm/kvm_host.h |  3 ---
 arch/x86/kvm/kvm_emulate.h      |  1 +
 arch/x86/kvm/mmu/paging_tmpl.h  | 14 +++++++-------
 arch/x86/kvm/vmx/nested.c       |  5 ++++-
 arch/x86/kvm/vmx/vmx.c          |  2 --
 5 files changed, 12 insertions(+), 13 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index ad5319a503f0..7ef4715d43d6 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -993,9 +993,6 @@ struct kvm_vcpu_arch {
 
 	u64 msr_kvm_poll_control;
 
-	/* set at EPT violation at this point */
-	unsigned long exit_qualification;
-
 	/* pv related host specific info */
 	struct {
 		bool pv_unhalted;
diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
index 4351149484fb..b5791a66637e 100644
--- a/arch/x86/kvm/kvm_emulate.h
+++ b/arch/x86/kvm/kvm_emulate.h
@@ -26,6 +26,7 @@ struct x86_exception {
 	bool nested_page_fault;
 	u64 address; /* cr2 or nested page fault gpa */
 	u8 async_page_fault;
+	unsigned long exit_qualification;
 };
 
 /*
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 4d4e98fe4f35..7a87097cb45b 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -497,21 +497,21 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
 	 * The other bits are set to 0.
 	 */
 	if (!(errcode & PFERR_RSVD_MASK)) {
-		vcpu->arch.exit_qualification &= (EPT_VIOLATION_GVA_IS_VALID |
-						  EPT_VIOLATION_GVA_TRANSLATED);
+		walker->fault.exit_qualification = 0;
+
 		if (write_fault)
-			vcpu->arch.exit_qualification |= EPT_VIOLATION_ACC_WRITE;
+			walker->fault.exit_qualification |= EPT_VIOLATION_ACC_WRITE;
 		if (user_fault)
-			vcpu->arch.exit_qualification |= EPT_VIOLATION_ACC_READ;
+			walker->fault.exit_qualification |= EPT_VIOLATION_ACC_READ;
 		if (fetch_fault)
-			vcpu->arch.exit_qualification |= EPT_VIOLATION_ACC_INSTR;
+			walker->fault.exit_qualification |= EPT_VIOLATION_ACC_INSTR;
 
 		/*
 		 * Note, pte_access holds the raw RWX bits from the EPTE, not
 		 * ACC_*_MASK flags!
 		 */
-		vcpu->arch.exit_qualification |= (pte_access & VMX_EPT_RWX_MASK) <<
-						 EPT_VIOLATION_RWX_SHIFT;
+		walker->fault.exit_qualification |= (pte_access & VMX_EPT_RWX_MASK) <<
+						     EPT_VIOLATION_RWX_SHIFT;
 	}
 #endif
 	walker->fault.address = addr;
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 994e014f8a50..15141b08c604 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -407,10 +407,13 @@ static void nested_ept_invalidate_addr(struct kvm_vcpu *vcpu, gpa_t eptp,
 static void nested_ept_inject_page_fault(struct kvm_vcpu *vcpu,
 		struct x86_exception *fault)
 {
+	unsigned long exit_qualification = fault->exit_qualification;
 	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	u32 vm_exit_reason;
-	unsigned long exit_qualification = vcpu->arch.exit_qualification;
+
+	exit_qualification |= vmx_get_exit_qual(vcpu) &
+			      (EPT_VIOLATION_GVA_IS_VALID | EPT_VIOLATION_GVA_TRANSLATED);
 
 	if (vmx->nested.pml_full) {
 		vm_exit_reason = EXIT_REASON_PML_FULL;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index e262bc2ba4e5..1de022af7dcb 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5771,8 +5771,6 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
 	error_code |= (exit_qualification & EPT_VIOLATION_GVA_TRANSLATED) != 0 ?
 	       PFERR_GUEST_FINAL_MASK : PFERR_GUEST_PAGE_MASK;
 
-	vcpu->arch.exit_qualification = exit_qualification;
-
 	/*
 	 * Check that the GPA doesn't exceed physical memory limits, as that is
 	 * a guest page fault.  We have to emulate the instruction here, because

base-commit: 873eef46b33c86be414d60bd00390e64fc0f006f
--