KVM: x86/mmu: Skip invalid roots when zapping leaf SPTEs for GFN range

When zapping a GFN in response to an APICv or MTRR change, don't zap SPTEs
for invalid roots as KVM only needs to ensure the guest can't use stale
mappings for the GFN.  Unlike kvm_tdp_mmu_unmap_gfn_range(), which must
zap "unreachable" SPTEs to ensure KVM doesn't mark a page accessed/dirty,
kvm_tdp_mmu_zap_leafs() isn't used (and isn't intended to be used) to
handle freeing of host memory.

Link: https://lore.kernel.org/r/20240111020048.844847-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

arch/x86/kvm/mmu/tdp_mmu.c

@@ -830,16 +830,16 @@ static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root,
 }
 
 /*
- * Zap leaf SPTEs for the range of gfns, [start, end), for all roots. Returns
- * true if a TLB flush is needed before releasing the MMU lock, i.e. if one or
- * more SPTEs were zapped since the MMU lock was last acquired.
+ * Zap leaf SPTEs for the range of gfns, [start, end), for all *VALID** roots.
+ * Returns true if a TLB flush is needed before releasing the MMU lock, i.e. if
+ * one or more SPTEs were zapped since the MMU lock was last acquired.
  */
 bool kvm_tdp_mmu_zap_leafs(struct kvm *kvm, gfn_t start, gfn_t end, bool flush)
 {
 	struct kvm_mmu_page *root;
 
 	lockdep_assert_held_write(&kvm->mmu_lock);
-	for_each_tdp_mmu_root_yield_safe(kvm, root)
+	for_each_valid_tdp_mmu_root_yield_safe(kvm, root, -1)
 		flush = tdp_mmu_zap_leafs(kvm, root, start, end, true, flush);
 
 	return flush;