KVM: cleanup: limit the number of pages per memory slot

Commit Message

Takuya Yoshikawa April 13, 2010, 1:47 p.m. UTC

None

Patch

===

This patch limits the number of pages per memory slot to make
us free from extra care about type issues.

Signed-off-by: Takuya Yoshikawa <[e-mail]>
---
 include/linux/kvm_host.h |    6 ++++++
 virt/kvm/kvm_main.c      |   11 ++++++-----
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 169d077..5583063 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -105,6 +105,12 @@  struct kvm_vcpu {
 	struct kvm_vcpu_arch arch;
 };
 
+/*
+ * Some of the bitops functions do not support too long bitmaps.
+ * This number must be determined not to exceed such limits.
+ */
+#define KVM_MEM_MAX_NR_PAGES ((1UL << 31) - 1)
+
 struct kvm_memory_slot {
 	gfn_t base_gfn;
 	unsigned long npages;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 6fe79c4..799ff1f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -553,6 +553,10 @@  int __kvm_set_memory_region(struct kvm *kvm,
 	base_gfn = mem->guest_phys_addr >> PAGE_SHIFT;
 	npages = mem->memory_size >> PAGE_SHIFT;
 
+	r = -EINVAL;
+	if (npages > KVM_MEM_MAX_NR_PAGES)
+		goto out;
+
 	if (!npages)
 		mem->flags &= ~KVM_MEM_LOG_DIRTY_PAGES;
 
@@ -1183,13 +1187,10 @@  void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
 	memslot = gfn_to_memslot_unaliased(kvm, gfn);
 	if (memslot && memslot->dirty_bitmap) {
 		unsigned long rel_gfn = gfn - memslot->base_gfn;
-		unsigned long *p = memslot->dirty_bitmap +
-					rel_gfn / BITS_PER_LONG;
-		int offset = rel_gfn % BITS_PER_LONG;
 
 		/* avoid RMW */
-		if (!generic_test_le_bit(offset, p))
-			generic___set_le_bit(offset, p);
+		if (!generic_test_le_bit(rel_gfn, memslot->dirty_bitmap))
+			generic___set_le_bit(rel_gfn, memslot->dirty_bitmap);
 	}
 }