Commit d7461823 authored by Sean Christopherson's avatar Sean Christopherson
Browse files

KVM: x86/mmu: Skip invalid TDP MMU roots when write-protecting SPTEs 

When write-protecting SPTEs, don't process invalid roots as invalid roots
are unreachable, i.e. can't be used to access guest memory and thus don't
need to be write-protected.

Note, this is *almost* a nop for kvm_tdp_mmu_clear_dirty_pt_masked(),
which is called under slots_lock, i.e. is mutually exclusive with
kvm_mmu_zap_all_fast().  But it's possible for something other than the
"fast zap" thread to grab a reference to an invalid root and thus keep a
root alive (but completely empty) after kvm_mmu_zap_all_fast() completes.

The kvm_tdp_mmu_write_protect_gfn() case is more interesting as KVM write-
protects SPTEs for reasons other than dirty logging, e.g. if a KVM creates
a SPTE for a nested VM while a fast zap is in-progress.

Add another TDP MMU iterator to visit only valid roots, and
opportunistically convert kvm_tdp_mmu_get_vcpu_root_hpa() to said iterator.

Link: https://lore.kernel.org/r/20240111020048.844847-6-seanjc@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent 99b85fda

arch/x86/kvm/mmu/tdp_mmu.c

+13 −9
Original line number Diff line number Diff line
@@ -171,12 +171,19 @@ static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm, 
 * Holding mmu_lock for write obviates the need for RCU protection as the list

 * is guaranteed to be stable.

 */

#define for_each_tdp_mmu_root(_kvm, _root, _as_id)				\

#define __for_each_tdp_mmu_root(_kvm, _root, _as_id, _only_valid)		\

	list_for_each_entry(_root, &_kvm->arch.tdp_mmu_roots, link)		\

		if (kvm_lockdep_assert_mmu_lock_held(_kvm, false) &&		\

		    _as_id >= 0 && kvm_mmu_page_as_id(_root) != _as_id) {	\

		    ((_as_id >= 0 && kvm_mmu_page_as_id(_root) != _as_id) ||	\

		     ((_only_valid) && (_root)->role.invalid))) {		\

		} else



#define for_each_tdp_mmu_root(_kvm, _root, _as_id)			\

	__for_each_tdp_mmu_root(_kvm, _root, _as_id, false)



#define for_each_valid_tdp_mmu_root(_kvm, _root, _as_id)		\

	__for_each_tdp_mmu_root(_kvm, _root, _as_id, true)



static struct kvm_mmu_page *tdp_mmu_alloc_sp(struct kvm_vcpu *vcpu)

{

	struct kvm_mmu_page *sp;
@@ -224,11 +231,8 @@ hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu) 


	lockdep_assert_held_write(&kvm->mmu_lock);



	/*

	 * Check for an existing root before allocating a new one.  Note, the

	 * role check prevents consuming an invalid root.

	 */

	for_each_tdp_mmu_root(kvm, root, kvm_mmu_role_as_id(role)) {

	/* Check for an existing root before allocating a new one. */

	for_each_valid_tdp_mmu_root(kvm, root, kvm_mmu_role_as_id(role)) {

		if (root->role.word == role.word &&

		    kvm_tdp_mmu_get_root(root))

			goto out;
@@ -1639,7 +1643,7 @@ void kvm_tdp_mmu_clear_dirty_pt_masked(struct kvm *kvm, 
{

	struct kvm_mmu_page *root;



	for_each_tdp_mmu_root(kvm, root, slot->as_id)

	for_each_valid_tdp_mmu_root(kvm, root, slot->as_id)

		clear_dirty_pt_masked(kvm, root, gfn, mask, wrprot);

}
@@ -1757,7 +1761,7 @@ bool kvm_tdp_mmu_write_protect_gfn(struct kvm *kvm, 
	bool spte_set = false;



	lockdep_assert_held_write(&kvm->mmu_lock);

	for_each_tdp_mmu_root(kvm, root, slot->as_id)

	for_each_valid_tdp_mmu_root(kvm, root, slot->as_id)

		spte_set |= write_protect_gfn(kvm, root, gfn, min_level);



	return spte_set;