KVM: Handle vma regions with no backing page

This patch allows VMAs that contain no backing page to be used for guest
memory.  This is useful for assigning mmio regions to a guest.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 37 insertions, 12 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b6a59498b5a7..f9dd20606c40 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -532,6 +532,7 @@ pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn)
         struct page *page[1];
         unsigned long addr;
         int npages;
+        pfn_t pfn;
 
         might_sleep();
 
@@ -544,19 +545,38 @@ pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn)
         npages = get_user_pages(current, current->mm, addr, 1, 1, 1, page,
                                 NULL);
 
-        if (npages != 1) {
-                get_page(bad_page);
-                return page_to_pfn(bad_page);
-        }
+        if (unlikely(npages != 1)) {
+                struct vm_area_struct *vma;
 
-        return page_to_pfn(page[0]);
+                vma = find_vma(current->mm, addr);
+                if (vma == NULL || addr < vma->vm_start ||
+                    !(vma->vm_flags & VM_PFNMAP)) {
+                        get_page(bad_page);
+                        return page_to_pfn(bad_page);
+                }
+
+                pfn = ((addr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
+                BUG_ON(pfn_valid(pfn));
+        } else
+                pfn = page_to_pfn(page[0]);
+
+        return pfn;
 }
 
 EXPORT_SYMBOL_GPL(gfn_to_pfn);
 
 struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
 {
-        return pfn_to_page(gfn_to_pfn(kvm, gfn));
+        pfn_t pfn;
+
+        pfn = gfn_to_pfn(kvm, gfn);
+        if (pfn_valid(pfn))
+                return pfn_to_page(pfn);
+
+        WARN_ON(!pfn_valid(pfn));
+
+        get_page(bad_page);
+        return bad_page;
 }
 
 EXPORT_SYMBOL_GPL(gfn_to_page);
@@ -569,7 +589,8 @@ EXPORT_SYMBOL_GPL(kvm_release_page_clean);
 
 void kvm_release_pfn_clean(pfn_t pfn)
 {
-        put_page(pfn_to_page(pfn));
+        if (pfn_valid(pfn))
+                put_page(pfn_to_page(pfn));
 }
 EXPORT_SYMBOL_GPL(kvm_release_pfn_clean);
 
@@ -594,21 +615,25 @@ EXPORT_SYMBOL_GPL(kvm_set_page_dirty);
 
 void kvm_set_pfn_dirty(pfn_t pfn)
 {
-        struct page *page = pfn_to_page(pfn);
-        if (!PageReserved(page))
-                SetPageDirty(page);
+        if (pfn_valid(pfn)) {
+                struct page *page = pfn_to_page(pfn);
+                if (!PageReserved(page))
+                        SetPageDirty(page);
+        }
 }
 EXPORT_SYMBOL_GPL(kvm_set_pfn_dirty);
 
 void kvm_set_pfn_accessed(pfn_t pfn)
 {
-        mark_page_accessed(pfn_to_page(pfn));
+        if (pfn_valid(pfn))
+                mark_page_accessed(pfn_to_page(pfn));
 }
 EXPORT_SYMBOL_GPL(kvm_set_pfn_accessed);
 
 void kvm_get_pfn(pfn_t pfn)
 {
-        get_page(pfn_to_page(pfn));
+        if (pfn_valid(pfn))
+                get_page(pfn_to_page(pfn));
 }
 EXPORT_SYMBOL_GPL(kvm_get_pfn);