linux-kernel - [PATCH v3 14/16] KVM: selftests: Set the user bit on nested NPT PTEs

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Message-ID: <20251127013440.3324671-15-yosry.ahmed@linux.dev>
Date: Thu, 27 Nov 2025 01:34:38 +0000
From: Yosry Ahmed <yosry.ahmed@...ux.dev>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
	kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Yosry Ahmed <yosry.ahmed@...ux.dev>
Subject: [PATCH v3 14/16] KVM: selftests: Set the user bit on nested NPT PTEs

According to the APM, NPT walks are treated as user accesses. In
preparation for supporting NPT mappings, set the 'user' bit on NPTs by
adding a mask of bits to always be set on PTEs in kvm_mmu.

Signed-off-by: Yosry Ahmed <yosry.ahmed@...ux.dev>
---
 tools/testing/selftests/kvm/include/x86/processor.h | 4 ++++
 tools/testing/selftests/kvm/lib/x86/processor.c     | 6 ++++--
 tools/testing/selftests/kvm/lib/x86/svm.c           | 3 +++
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/x86/processor.h b/tools/testing/selftests/kvm/include/x86/processor.h
index 920abd14f3a6..d41245e2521b 100644
--- a/tools/testing/selftests/kvm/include/x86/processor.h
+++ b/tools/testing/selftests/kvm/include/x86/processor.h
@@ -1450,6 +1450,8 @@ struct pte_masks {
 	uint64_t x;
 	uint64_t c;
 	uint64_t s;
+
+	uint64_t always_set;
 };
 
 struct kvm_mmu {
@@ -1469,6 +1471,8 @@ struct kvm_mmu {
 #define PTE_C_MASK(mmu) ((mmu)->pte_masks.c)
 #define PTE_S_MASK(mmu) ((mmu)->pte_masks.s)
 
+#define PTE_ALWAYS_SET_MASK(mmu) ((mmu)->pte_masks.always_set)
+
 #define pte_present(mmu, pte) (!!(*(pte) & PTE_PRESENT_MASK(mmu)))
 #define pte_writable(mmu, pte) (!!(*(pte) & PTE_WRITABLE_MASK(mmu)))
 #define pte_user(mmu, pte) (!!(*(pte) & PTE_USER_MASK(mmu)))
diff --git a/tools/testing/selftests/kvm/lib/x86/processor.c b/tools/testing/selftests/kvm/lib/x86/processor.c
index b22c8c1bfdc3..749ae7522473 100644
--- a/tools/testing/selftests/kvm/lib/x86/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86/processor.c
@@ -227,7 +227,8 @@ static uint64_t *virt_create_upper_pte(struct kvm_vm *vm,
 	paddr = vm_untag_gpa(vm, paddr);
 
 	if (!pte_present(mmu, pte)) {
-		*pte = PTE_PRESENT_MASK(mmu) | PTE_WRITABLE_MASK(mmu) | PTE_X_MASK(mmu);
+		*pte = PTE_PRESENT_MASK(mmu) | PTE_WRITABLE_MASK(mmu)
+			| PTE_X_MASK(mmu) | PTE_ALWAYS_SET_MASK(mmu);
 		if (current_level == target_level)
 			*pte |= PTE_HUGE_MASK(mmu) | (paddr & PHYSICAL_PAGE_MASK);
 		else
@@ -293,7 +294,8 @@ void __virt_pg_map(struct kvm_vm *vm, struct kvm_mmu *mmu, uint64_t vaddr,
 	pte = virt_get_pte(vm, mmu, pte, vaddr, PG_LEVEL_4K);
 	TEST_ASSERT(!pte_present(mmu, pte),
 		    "PTE already present for 4k page at vaddr: 0x%lx", vaddr);
-	*pte = PTE_PRESENT_MASK(mmu) | PTE_WRITABLE_MASK(mmu) | PTE_X_MASK(mmu)
+	*pte = PTE_PRESENT_MASK(mmu) | PTE_WRITABLE_MASK(mmu)
+		| PTE_X_MASK(mmu) | PTE_ALWAYS_SET_MASK(mmu)
 		| (paddr & PHYSICAL_PAGE_MASK);
 
 	/*
diff --git a/tools/testing/selftests/kvm/lib/x86/svm.c b/tools/testing/selftests/kvm/lib/x86/svm.c
index cf3b98802164..838f218545af 100644
--- a/tools/testing/selftests/kvm/lib/x86/svm.c
+++ b/tools/testing/selftests/kvm/lib/x86/svm.c
@@ -73,6 +73,9 @@ void vm_enable_npt(struct kvm_vm *vm)
 	pte_masks.c = 0;
 	pte_masks.s = 0;
 
+	/* NPT walks are treated as user accesses, so set the 'user' bit */
+	pte_masks.always_set = pte_masks.user;
+
 	vm->arch.nested.mmu = mmu_create(vm, vm->pgtable_levels, &pte_masks);
 }
 
-- 
2.52.0.158.g65b55ccf14-goog