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@google.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

On Tue, Oct 28, 2025 at 03:30:40PM -0700, Jim Mattson wrote:
> 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@google.com>

Reviewed-by: Yosry Ahmed <yosry.ahmed@linux.dev>

> ---
>  .../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
>