linux-kernel - [PATCH v2 2/4] KVM: selftests: Use a loop to walk guest page tables

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Message-ID: <20251028225827.2269128-3-jmattson@google.com>
Date: Tue, 28 Oct 2025 15:30:40 -0700
From: Jim Mattson <jmattson@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Shuah Khan <shuah@...nel.org>, 
	Sean Christopherson <seanjc@...gle.com>, Marc Zyngier <maz@...nel.org>, 
	Oliver Upton <oliver.upton@...ux.dev>, Joey Gouly <joey.gouly@....com>, 
	Suzuki K Poulose <suzuki.poulose@....com>, Zenghui Yu <yuzenghui@...wei.com>, 
	Andrew Jones <ajones@...tanamicro.com>, Huacai Chen <chenhuacai@...nel.org>, 
	Bibo Mao <maobibo@...ngson.cn>, Jim Mattson <jmattson@...gle.com>, 
	"Pratik R. Sampat" <prsampat@....com>, James Houghton <jthoughton@...gle.com>, linux-kernel@...r.kernel.org, 
	kvm@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev
Subject: [PATCH v2 2/4] KVM: selftests: Use a loop to walk guest page tables

Walk the guest page tables via a loop when searching for a PTE,
instead of using unique variables for each level of the page tables.

This simplifies the code and makes it easier to support 5-level paging
in the future.

Signed-off-by: Jim Mattson <jmattson@...gle.com>
---
 .../testing/selftests/kvm/lib/x86/processor.c | 23 ++++++++-----------
 1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/tools/testing/selftests/kvm/lib/x86/processor.c b/tools/testing/selftests/kvm/lib/x86/processor.c
index 738f2a44083f..720c678187b5 100644
--- a/tools/testing/selftests/kvm/lib/x86/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86/processor.c
@@ -307,7 +307,8 @@ static bool vm_is_target_pte(uint64_t *pte, int *level, int current_level)
 uint64_t *__vm_get_page_table_entry(struct kvm_vm *vm, uint64_t vaddr,
 				    int *level)
 {
-	uint64_t *pml4e, *pdpe, *pde;
+	uint64_t *pte = &vm->pgd;
+	int current_level;
 
 	TEST_ASSERT(!vm->arch.is_pt_protected,
 		    "Walking page tables of protected guests is impossible");
@@ -328,19 +329,15 @@ uint64_t *__vm_get_page_table_entry(struct kvm_vm *vm, uint64_t vaddr,
 	TEST_ASSERT(vaddr == (((int64_t)vaddr << 16) >> 16),
 		"Canonical check failed.  The virtual address is invalid.");
 
-	pml4e = virt_get_pte(vm, &vm->pgd, vaddr, PG_LEVEL_512G);
-	if (vm_is_target_pte(pml4e, level, PG_LEVEL_512G))
-		return pml4e;
-
-	pdpe = virt_get_pte(vm, pml4e, vaddr, PG_LEVEL_1G);
-	if (vm_is_target_pte(pdpe, level, PG_LEVEL_1G))
-		return pdpe;
-
-	pde = virt_get_pte(vm, pdpe, vaddr, PG_LEVEL_2M);
-	if (vm_is_target_pte(pde, level, PG_LEVEL_2M))
-		return pde;
+	for (current_level = vm->pgtable_levels;
+	     current_level > PG_LEVEL_4K;
+	     current_level--) {
+		pte = virt_get_pte(vm, pte, vaddr, current_level);
+		if (vm_is_target_pte(pte, level, current_level))
+			return pte;
+	}
 
-	return virt_get_pte(vm, pde, vaddr, PG_LEVEL_4K);
+	return virt_get_pte(vm, pte, vaddr, PG_LEVEL_4K);
 }
 
 uint64_t *vm_get_page_table_entry(struct kvm_vm *vm, uint64_t vaddr)
-- 
2.51.1.851.g4ebd6896fd-goog