linux-kernel - [RFC PATCH 02/18] KVM: nVMX: Decouple EPT RWX bits from EPT Violation protection bits

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Message-ID: <20250313203702.575156-3-jon@nutanix.com>
Date: Thu, 13 Mar 2025 13:36:41 -0700
From: Jon Kohler <jon@...anix.com>
To: seanjc@...gle.com, pbonzini@...hat.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc: Jon Kohler <jon@...anix.com>, Nikolay Borisov <nik.borisov@...e.com>
Subject: [RFC PATCH 02/18] KVM: nVMX: Decouple EPT RWX bits from EPT Violation protection bits

From: Sean Christopherson <seanjc@...gle.com>

Define independent macros for the RWX protection bits that are enumerated
via EXIT_QUALIFICATION for EPT Violations, and tie them to the RWX bits in
EPT entries via compile-time asserts.  Piggybacking the EPTE defines works
for now, but it creates holes in the EPT_VIOLATION_xxx macros and will
cause headaches if/when KVM emulates Mode-Based Execution (MBEC), or any
other features that introduces additional protection information.

Opportunistically rename EPT_VIOLATION_RWX_MASK to EPT_VIOLATION_PROT_MASK
so that it doesn't become stale if/when MBEC support is added.

No functional change intended.

Cc: Jon Kohler <jon@...anix.com>
Cc: Nikolay Borisov <nik.borisov@...e.com>
Reviewed-by: Nikolay Borisov <nik.borisov@...e.com>
Link: https://lore.kernel.org/r/20250227000705.3199706-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
(cherry picked from commit 61146f67e4cb67064ce3003d94ee19302d314fff)
(cherry picked from commit 8cddacdb6a6a459c9425b4abd4c982cec89c25e4)

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

diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
index aabc223c6498..8707361b24da 100644
--- a/arch/x86/include/asm/vmx.h
+++ b/arch/x86/include/asm/vmx.h
@@ -580,14 +580,23 @@ enum vm_entry_failure_code {
 /*
  * Exit Qualifications for EPT Violations
  */
-#define EPT_VIOLATION_RWX_SHIFT		3
 #define EPT_VIOLATION_ACC_READ		BIT(0)
 #define EPT_VIOLATION_ACC_WRITE		BIT(1)
 #define EPT_VIOLATION_ACC_INSTR		BIT(2)
-#define EPT_VIOLATION_RWX_MASK		(VMX_EPT_RWX_MASK << EPT_VIOLATION_RWX_SHIFT)
+#define EPT_VIOLATION_PROT_READ		BIT(3)
+#define EPT_VIOLATION_PROT_WRITE	BIT(4)
+#define EPT_VIOLATION_PROT_EXEC		BIT(5)
+#define EPT_VIOLATION_PROT_MASK		(EPT_VIOLATION_PROT_READ  | \
+					 EPT_VIOLATION_PROT_WRITE | \
+					 EPT_VIOLATION_PROT_EXEC)
 #define EPT_VIOLATION_GVA_IS_VALID	BIT(7)
 #define EPT_VIOLATION_GVA_TRANSLATED	BIT(8)
 
+#define EPT_VIOLATION_RWX_TO_PROT(__epte) (((__epte) & VMX_EPT_RWX_MASK) << 3)
+
+static_assert(EPT_VIOLATION_RWX_TO_PROT(VMX_EPT_RWX_MASK) ==
+	      (EPT_VIOLATION_PROT_READ | EPT_VIOLATION_PROT_WRITE | EPT_VIOLATION_PROT_EXEC));
+
 /*
  * Exit Qualifications for NOTIFY VM EXIT
  */
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index ae7d39ff2d07..9bc3fc4a238b 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -510,8 +510,7 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
 		 * Note, pte_access holds the raw RWX bits from the EPTE, not
 		 * ACC_*_MASK flags!
 		 */
-		walker->fault.exit_qualification |= (pte_access & VMX_EPT_RWX_MASK) <<
-						     EPT_VIOLATION_RWX_SHIFT;
+		walker->fault.exit_qualification |= EPT_VIOLATION_RWX_TO_PROT(pte_access);
 	}
 #endif
 	walker->fault.address = addr;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 87206dabf020..7a98f03ef146 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5831,7 +5831,7 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
 	error_code |= (exit_qualification & EPT_VIOLATION_ACC_INSTR)
 		      ? PFERR_FETCH_MASK : 0;
 	/* ept page table entry is present? */
-	error_code |= (exit_qualification & EPT_VIOLATION_RWX_MASK)
+	error_code |= (exit_qualification & EPT_VIOLATION_PROT_MASK)
 		      ? PFERR_PRESENT_MASK : 0;
 
 	if (error_code & EPT_VIOLATION_GVA_IS_VALID)
-- 
2.43.0