KVM: MMU: Make gfn_to_page() always safe
In case the page is not present in the guest memory map, return a dummy
page the guest can scribble on.
This simplifies error checking in its users.
Signed-off-by: Izik Eidus <izike@qumranet.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index 1879b40..47000be 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -993,6 +993,12 @@
return r;
}
+int is_error_page(struct page *page)
+{
+ return page == bad_page;
+}
+EXPORT_SYMBOL_GPL(is_error_page);
+
gfn_t unalias_gfn(struct kvm *kvm, gfn_t gfn)
{
int i;
@@ -1034,7 +1040,7 @@
gfn = unalias_gfn(kvm, gfn);
slot = __gfn_to_memslot(kvm, gfn);
if (!slot)
- return NULL;
+ return bad_page;
return slot->phys_mem[gfn - slot->base_gfn];
}
EXPORT_SYMBOL_GPL(gfn_to_page);
@@ -1054,7 +1060,7 @@
struct page *page;
page = gfn_to_page(kvm, gfn);
- if (!page)
+ if (is_error_page(page))
return -EFAULT;
page_virt = kmap_atomic(page, KM_USER0);
@@ -1092,7 +1098,7 @@
struct page *page;
page = gfn_to_page(kvm, gfn);
- if (!page)
+ if (is_error_page(page))
return -EFAULT;
page_virt = kmap_atomic(page, KM_USER0);
@@ -1130,7 +1136,7 @@
struct page *page;
page = gfn_to_page(kvm, gfn);
- if (!page)
+ if (is_error_page(page))
return -EFAULT;
page_virt = kmap_atomic(page, KM_USER0);
@@ -3068,7 +3074,7 @@
pgoff = ((address - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
page = gfn_to_page(kvm, pgoff);
- if (!page)
+ if (is_error_page(page))
return NOPAGE_SIGBUS;
get_page(page);
if (type != NULL)
@@ -3383,7 +3389,7 @@
.cls = &kvm_sysdev_class,
};
-hpa_t bad_page_address;
+struct page *bad_page;
static inline
struct kvm_vcpu *preempt_notifier_to_vcpu(struct preempt_notifier *pn)
@@ -3512,7 +3518,6 @@
static __init int kvm_init(void)
{
- static struct page *bad_page;
int r;
r = kvm_mmu_module_init();
@@ -3523,16 +3528,13 @@
kvm_arch_init();
- bad_page = alloc_page(GFP_KERNEL);
+ bad_page = alloc_page(GFP_KERNEL | __GFP_ZERO);
if (bad_page == NULL) {
r = -ENOMEM;
goto out;
}
- bad_page_address = page_to_pfn(bad_page) << PAGE_SHIFT;
- memset(__va(bad_page_address), 0, PAGE_SIZE);
-
return 0;
out:
@@ -3545,7 +3547,7 @@
static __exit void kvm_exit(void)
{
kvm_exit_debug();
- __free_page(pfn_to_page(bad_page_address >> PAGE_SHIFT));
+ __free_page(bad_page);
kvm_mmu_module_exit();
}