Commit c834e5e4 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: x86/mmu: Use '0' as the one and only value for an invalid PAE root 



Use '0' to denote an invalid pae_root instead of '0' or INVALID_PAGE.
Unlike root_hpa, the pae_roots hold permission bits and thus are
guaranteed to be non-zero.  Having to deal with both values leads to
bugs, e.g. failing to set back to INVALID_PAGE, warning on the wrong
value, etc...

Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20210309224207.1218275-4-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 978c834a

arch/x86/kvm/mmu/mmu.c

+13 −11
Original line number Diff line number Diff line
@@ -3197,11 +3197,14 @@ void kvm_mmu_free_roots(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu, 
		    (mmu->root_level >= PT64_ROOT_4LEVEL || mmu->direct_map)) {

			mmu_free_root_page(kvm, &mmu->root_hpa, &invalid_list);

		} else if (mmu->pae_root) {

			for (i = 0; i < 4; ++i)

				if (mmu->pae_root[i] != 0)

					mmu_free_root_page(kvm,

							   &mmu->pae_root[i],

			for (i = 0; i < 4; ++i) {

				if (!IS_VALID_PAE_ROOT(mmu->pae_root[i]))

					continue;



				mmu_free_root_page(kvm, &mmu->pae_root[i],

						   &invalid_list);

				mmu->pae_root[i] = INVALID_PAE_ROOT;

			}

		}

		mmu->root_hpa = INVALID_PAGE;

		mmu->root_pgd = 0;
@@ -3253,8 +3256,7 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu) 
			return -EIO;



		for (i = 0; i < 4; ++i) {

			WARN_ON_ONCE(mmu->pae_root[i] &&

				     VALID_PAGE(mmu->pae_root[i]));

			WARN_ON_ONCE(IS_VALID_PAE_ROOT(mmu->pae_root[i]));



			root = mmu_alloc_root(vcpu, i << (30 - PAGE_SHIFT),

					      i << 30, PT32_ROOT_LEVEL, true);
@@ -3328,11 +3330,11 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu) 
	}



	for (i = 0; i < 4; ++i) {

		WARN_ON_ONCE(mmu->pae_root[i] && VALID_PAGE(mmu->pae_root[i]));

		WARN_ON_ONCE(IS_VALID_PAE_ROOT(mmu->pae_root[i]));



		if (mmu->root_level == PT32E_ROOT_LEVEL) {

			if (!(pdptrs[i] & PT_PRESENT_MASK)) {

				mmu->pae_root[i] = 0;

				mmu->pae_root[i] = INVALID_PAE_ROOT;

				continue;

			}

			root_gfn = pdptrs[i] >> PAGE_SHIFT;
@@ -3450,7 +3452,7 @@ void kvm_mmu_sync_roots(struct kvm_vcpu *vcpu) 
	for (i = 0; i < 4; ++i) {

		hpa_t root = vcpu->arch.mmu->pae_root[i];



		if (root && VALID_PAGE(root)) {

		if (IS_VALID_PAE_ROOT(root)) {

			root &= PT64_BASE_ADDR_MASK;

			sp = to_shadow_page(root);

			mmu_sync_children(vcpu, sp);
@@ -5307,7 +5309,7 @@ static int __kvm_mmu_create(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu) 


	mmu->pae_root = page_address(page);

	for (i = 0; i < 4; ++i)

		mmu->pae_root[i] = INVALID_PAGE;

		mmu->pae_root[i] = INVALID_PAE_ROOT;



	return 0;

}

arch/x86/kvm/mmu/mmu_audit.c

+1 −1
Original line number Diff line number Diff line
@@ -70,7 +70,7 @@ static void mmu_spte_walk(struct kvm_vcpu *vcpu, inspect_spte_fn fn) 
	for (i = 0; i < 4; ++i) {

		hpa_t root = vcpu->arch.mmu->pae_root[i];



		if (root && VALID_PAGE(root)) {

		if (IS_VALID_PAE_ROOT(root)) {

			root &= PT64_BASE_ADDR_MASK;

			sp = to_shadow_page(root);

			__mmu_spte_walk(vcpu, sp, fn, 2);

arch/x86/kvm/mmu/mmu_internal.h

+10 −0
Original line number Diff line number Diff line
@@ -20,6 +20,16 @@ extern bool dbg; 
#define MMU_WARN_ON(x) do { } while (0)

#endif



/*

 * Unlike regular MMU roots, PAE "roots", a.k.a. PDPTEs/PDPTRs, have a PRESENT

 * bit, and thus are guaranteed to be non-zero when valid.  And, when a guest

 * PDPTR is !PRESENT, its corresponding PAE root cannot be set to INVALID_PAGE,

 * as the CPU would treat that as PRESENT PDPTR with reserved bits set.  Use

 * '0' instead of INVALID_PAGE to indicate an invalid PAE root.

 */

#define INVALID_PAE_ROOT	0

#define IS_VALID_PAE_ROOT(x)	(!!(x))



struct kvm_mmu_page {

	struct list_head link;

	struct hlist_node hash_link;