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@linux.dev>
Link: https://patch.msgid.link/20251230230150.4150236-18-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/tools/testing/selftests/kvm/include/x86/kvm_util_arch.h b/tools/testing/selftests/kvm/include/x86/kvm_util_arch.h
index 1cf84b8212c62417e45300d8fa7e21261ac2bc0c..be35d26bb32005e21378edcc924aee6ed3fa464e 100644 (file)
--- a/tools/testing/selftests/kvm/include/x86/kvm_util_arch.h
+++ b/tools/testing/selftests/kvm/include/x86/kvm_util_arch.h
@@ -22,6 +22,8 @@ struct pte_masks {
        uint64_t nx;
        uint64_t c;
        uint64_t s;
+
+       uint64_t always_set;
 };
 
 struct kvm_mmu_arch {

diff --git a/tools/testing/selftests/kvm/include/x86/processor.h b/tools/testing/selftests/kvm/include/x86/processor.h
index 115bec5eb1ebb2ccfcbccfeddf843c11ed55467b..995277cae94edd4633e2a9b2fd2297f9985f950f 100644 (file)
--- a/tools/testing/selftests/kvm/include/x86/processor.h
+++ b/tools/testing/selftests/kvm/include/x86/processor.h
@@ -1452,6 +1452,7 @@ enum pg_level {
 #define PTE_NX_MASK(mmu)               ((mmu)->arch.pte_masks.nx)
 #define PTE_C_BIT_MASK(mmu)            ((mmu)->arch.pte_masks.c)
 #define PTE_S_BIT_MASK(mmu)            ((mmu)->arch.pte_masks.s)
+#define PTE_ALWAYS_SET_MASK(mmu)       ((mmu)->arch.pte_masks.always_set)
 
 /*
  * For PTEs without a PRESENT bit (i.e. EPT entries), treat the PTE as present

diff --git a/tools/testing/selftests/kvm/lib/x86/processor.c b/tools/testing/selftests/kvm/lib/x86/processor.c
index a3a4c9a4cbcbd34650744a428a91f11761351973..5a3385d489024d66d5d6ecc20e942677064051f8 100644 (file)
--- a/tools/testing/selftests/kvm/lib/x86/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86/processor.c
@@ -231,7 +231,8 @@ static uint64_t *virt_create_upper_pte(struct kvm_vm *vm,
 
        if (!is_present_pte(mmu, pte)) {
                *pte = PTE_PRESENT_MASK(mmu) | PTE_READABLE_MASK(mmu) |
-                      PTE_WRITABLE_MASK(mmu) | PTE_EXECUTABLE_MASK(mmu);
+                      PTE_WRITABLE_MASK(mmu) | PTE_EXECUTABLE_MASK(mmu) |
+                      PTE_ALWAYS_SET_MASK(mmu);
                if (current_level == target_level)
                        *pte |= PTE_HUGE_MASK(mmu) | (paddr & PHYSICAL_PAGE_MASK);
                else
@@ -299,7 +300,7 @@ void __virt_pg_map(struct kvm_vm *vm, struct kvm_mmu *mmu, uint64_t vaddr,
                    "PTE already present for 4k page at vaddr: 0x%lx", vaddr);
        *pte = PTE_PRESENT_MASK(mmu) | PTE_READABLE_MASK(mmu) |
               PTE_WRITABLE_MASK(mmu) | PTE_EXECUTABLE_MASK(mmu) |
-              (paddr & PHYSICAL_PAGE_MASK);
+              PTE_ALWAYS_SET_MASK(mmu) | (paddr & PHYSICAL_PAGE_MASK);
 
        /*
         * Neither SEV nor TDX supports shared page tables, so only the final

diff --git a/tools/testing/selftests/kvm/lib/x86/svm.c b/tools/testing/selftests/kvm/lib/x86/svm.c
index a25a3471f5f6749621e0370400dac8ef4d684469..2e5c480c9afd481077c0f12db42e577f9fc54736 100644 (file)
--- a/tools/testing/selftests/kvm/lib/x86/svm.c
+++ b/tools/testing/selftests/kvm/lib/x86/svm.c
@@ -75,6 +75,9 @@ void vm_enable_npt(struct kvm_vm *vm)
        pte_masks = vm->mmu.arch.pte_masks;
        pte_masks.c = 0;
 
+       /* NPT walks are treated as user accesses, so set the 'user' bit. */
+       pte_masks.always_set = pte_masks.user;
+
        tdp_mmu_init(vm, vm->mmu.pgtable_levels, &pte_masks);
 }