KVM: Disable large pages on misaligned memory slots

If a slots guest physical address and host virtual address unequal (mod large page size), then we would erronously try to back guest large pages with host large pages. Detect this misalignment and diable large page support for the trouble slot. Cc: [email protected] Signed-off-by: Avi Kivity <[email protected]>
iegor · Jun 10, 2009 · ac04527 · ac04527
1 parent a0861c0
commit ac04527
Showing 1 changed file with 9 additions and 1 deletion.
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
@@ -1086,7 +1086,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 {
 	int r;
 	gfn_t base_gfn;
-	unsigned long npages;
+	unsigned long npages, ugfn;
 	int largepages;
 	unsigned long i;
 	struct kvm_memory_slot *memslot;
@@ -1177,6 +1177,14 @@ int __kvm_set_memory_region(struct kvm *kvm,
 			new.lpage_info[0].write_count = 1;
 		if ((base_gfn+npages) % KVM_PAGES_PER_HPAGE)
 			new.lpage_info[largepages-1].write_count = 1;
+		ugfn = new.userspace_addr >> PAGE_SHIFT;
+		/*
+		 * If the gfn and userspace address are not aligned wrt each
+		 * other, disable large page support for this slot
+		 */
+		if ((base_gfn ^ ugfn) & (KVM_PAGES_PER_HPAGE - 1))
+			for (i = 0; i < largepages; ++i)
+				new.lpage_info[i].write_count = 1;
 	}
 
 	/* Allocate page dirty bitmap if needed */