KVM: x86/mmu: Extend make_huge_page_split_spte() for the shadow MMU

Currently make_huge_page_split_spte() assumes execute permissions can be
granted to any 4K SPTE when splitting huge pages. This is true for the
TDP MMU but is not necessarily true for the shadow MMU, since KVM may be
shadowing a non-executable huge page.

To fix this, pass in the role of the child shadow page where the huge
page will be split and derive the execution permission from that.  This
is correct because huge pages are always split with direct shadow page
and thus the shadow page role contains the correct access permissions.

No functional change intended.

Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20220516232138.1783324-19-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 7 insertions, 8 deletions

diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
index db294c1beea2..fb1f17504138 100644
--- a/arch/x86/kvm/mmu/spte.c
+++ b/arch/x86/kvm/mmu/spte.c
@@ -246,11 +246,10 @@ static u64 make_spte_executable(u64 spte)
  * This is used during huge page splitting to build the SPTEs that make up the
  * new page table.
  */
-u64 make_huge_page_split_spte(struct kvm *kvm, u64 huge_spte, int huge_level,
+u64 make_huge_page_split_spte(struct kvm *kvm, u64 huge_spte, union kvm_mmu_page_role role,
 			      int index)
 {
 	u64 child_spte;
-	int child_level;
 
 	if (WARN_ON_ONCE(!is_shadow_present_pte(huge_spte)))
 		return 0;
@@ -259,23 +258,23 @@ u64 make_huge_page_split_spte(struct kvm *kvm, u64 huge_spte, int huge_level,
 		return 0;
 
 	child_spte = huge_spte;
-	child_level = huge_level - 1;
 
 	/*
 	 * The child_spte already has the base address of the huge page being
 	 * split. So we just have to OR in the offset to the page at the next
 	 * lower level for the given index.
 	 */
-	child_spte |= (index * KVM_PAGES_PER_HPAGE(child_level)) << PAGE_SHIFT;
+	child_spte |= (index * KVM_PAGES_PER_HPAGE(role.level)) << PAGE_SHIFT;
 
-	if (child_level == PG_LEVEL_4K) {
+	if (role.level == PG_LEVEL_4K) {
 		child_spte &= ~PT_PAGE_SIZE_MASK;
 
 		/*
-		 * When splitting to a 4K page, mark the page executable as the
-		 * NX hugepage mitigation no longer applies.
+		 * When splitting to a 4K page where execution is allowed, mark
+		 * the page executable as the NX hugepage mitigation no longer
+		 * applies.
 		 */
-		if (is_nx_huge_page_enabled(kvm))
+		if ((role.access & ACC_EXEC_MASK) && is_nx_huge_page_enabled(kvm))
 			child_spte = make_spte_executable(child_spte);
 	}