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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>
This commit is contained in:
Izik Eidus 2007-10-17 19:17:48 +02:00 committed by Avi Kivity
parent 9647c14c98
commit cea7bb2128
4 changed files with 23 additions and 29 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
drivers/kvm/kvm.h
View File

@ -565,8 +565,9 @@ static inline int is_error_hpa(hpa_t hpa) { return hpa >> HPA_MSB; }
hpa_t gva_to_hpa(struct kvm_vcpu *vcpu, gva_t gva);
struct page *gva_to_page(struct kvm_vcpu *vcpu, gva_t gva);
extern hpa_t bad_page_address;
extern struct page *bad_page;
int is_error_page(struct page *page);
gfn_t unalias_gfn(struct kvm *kvm, gfn_t gfn);
struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn);
int kvm_read_guest_page(struct kvm *kvm, gfn_t gfn, void *data, int offset,

26
drivers/kvm/kvm_main.c
View File

@ -993,6 +993,12 @@ static int kvm_vm_ioctl_set_irqchip(struct kvm *kvm, struct kvm_irqchip *chip)
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 @@ struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
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 @@ int kvm_read_guest_page(struct kvm *kvm, gfn_t gfn, void *data, int offset,
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 @@ int kvm_write_guest_page(struct kvm *kvm, gfn_t gfn, const void *data,
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 @@ int kvm_clear_guest_page(struct kvm *kvm, gfn_t gfn, int offset, int len)
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 @@ static struct page *kvm_vm_nopage(struct vm_area_struct *vma,
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 @@ static struct sys_device kvm_sysdev = {
.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 @@ EXPORT_SYMBOL_GPL(kvm_exit_x86);
static __init int kvm_init(void)
{
static struct page *bad_page;
int r;
r = kvm_mmu_module_init();
@ -3523,16 +3528,13 @@ static __init int kvm_init(void)
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 @@ out4:
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();
}

16
drivers/kvm/mmu.c
View File

@ -850,23 +850,17 @@ static void page_header_update_slot(struct kvm *kvm, void *pte, gpa_t gpa)
__set_bit(slot, &page_head->slot_bitmap);
}
hpa_t safe_gpa_to_hpa(struct kvm *kvm, gpa_t gpa)
{
hpa_t hpa = gpa_to_hpa(kvm, gpa);
return is_error_hpa(hpa) ? bad_page_address | (gpa & ~PAGE_MASK): hpa;
}
hpa_t gpa_to_hpa(struct kvm *kvm, gpa_t gpa)
{
struct page *page;
hpa_t hpa;
ASSERT((gpa & HPA_ERR_MASK) == 0);
page = gfn_to_page(kvm, gpa >> PAGE_SHIFT);
if (!page)
return gpa | HPA_ERR_MASK;
return ((hpa_t)page_to_pfn(page) << PAGE_SHIFT)
| (gpa & (PAGE_SIZE-1));
hpa = ((hpa_t)page_to_pfn(page) << PAGE_SHIFT) | (gpa & (PAGE_SIZE-1));
if (is_error_page(page))
return hpa | HPA_ERR_MASK;
return hpa;
}
hpa_t gva_to_hpa(struct kvm_vcpu *vcpu, gva_t gva)

7
drivers/kvm/paging_tmpl.h
View File

@ -72,8 +72,6 @@ static int FNAME(walk_addr)(struct guest_walker *walker,
struct kvm_vcpu *vcpu, gva_t addr,
int write_fault, int user_fault, int fetch_fault)
{
hpa_t hpa;
struct kvm_memory_slot *slot;
struct page *page;
pt_element_t *table;
pt_element_t pte;
@ -105,9 +103,8 @@ static int FNAME(walk_addr)(struct guest_walker *walker,
pgprintk("%s: table_gfn[%d] %lx\n", __FUNCTION__,
walker->level - 1, table_gfn);
slot = gfn_to_memslot(vcpu->kvm, table_gfn);
hpa = safe_gpa_to_hpa(vcpu->kvm, pte & PT64_BASE_ADDR_MASK);
page = pfn_to_page(hpa >> PAGE_SHIFT);
page = gfn_to_page(vcpu->kvm, (pte & PT64_BASE_ADDR_MASK)
>> PAGE_SHIFT);
table = kmap_atomic(page, KM_USER0);
pte = table[index];