KVM: propagate fault r/w information to gup(), allow read-only memory

As suggested by Andrea, pass r/w error code to gup(), upgrading read fault
to writable if host pte allows it.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 41 insertions, 10 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 475a100f3a22..2803b4db2a38 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -959,7 +959,7 @@ static pfn_t get_fault_pfn(void)
 }
 
 static pfn_t hva_to_pfn(struct kvm *kvm, unsigned long addr, bool atomic,
-                        bool *async)
+                        bool *async, bool write_fault, bool *writable)
 {
         struct page *page[1];
         int npages = 0;
@@ -968,12 +968,34 @@ static pfn_t hva_to_pfn(struct kvm *kvm, unsigned long addr, bool atomic,
         /* we can do it either atomically or asynchronously, not both */
         BUG_ON(atomic && async);
 
+        BUG_ON(!write_fault && !writable);
+
+        if (writable)
+                *writable = true;
+
         if (atomic || async)
                 npages = __get_user_pages_fast(addr, 1, 1, page);
 
         if (unlikely(npages != 1) && !atomic) {
                 might_sleep();
-                npages = get_user_pages_fast(addr, 1, 1, page);
+
+                if (writable)
+                        *writable = write_fault;
+
+                npages = get_user_pages_fast(addr, 1, write_fault, page);
+
+                /* map read fault as writable if possible */
+                if (unlikely(!write_fault) && npages == 1) {
+                        struct page *wpage[1];
+
+                        npages = __get_user_pages_fast(addr, 1, 1, wpage);
+                        if (npages == 1) {
+                                *writable = true;
+                                put_page(page[0]);
+                                page[0] = wpage[0];
+                        }
+                        npages = 1;
+                }
         }
 
         if (unlikely(npages != 1)) {
@@ -1011,11 +1033,12 @@ static pfn_t hva_to_pfn(struct kvm *kvm, unsigned long addr, bool atomic,
 
 pfn_t hva_to_pfn_atomic(struct kvm *kvm, unsigned long addr)
 {
-        return hva_to_pfn(kvm, addr, true, NULL);
+        return hva_to_pfn(kvm, addr, true, NULL, true, NULL);
 }
 EXPORT_SYMBOL_GPL(hva_to_pfn_atomic);
 
-static pfn_t __gfn_to_pfn(struct kvm *kvm, gfn_t gfn, bool atomic, bool *async)
+static pfn_t __gfn_to_pfn(struct kvm *kvm, gfn_t gfn, bool atomic, bool *async,
+                          bool write_fault, bool *writable)
 {
         unsigned long addr;
 
@@ -1028,32 +1051,40 @@ static pfn_t __gfn_to_pfn(struct kvm *kvm, gfn_t gfn, bool atomic, bool *async)
                 return page_to_pfn(bad_page);
         }
 
-        return hva_to_pfn(kvm, addr, atomic, async);
+        return hva_to_pfn(kvm, addr, atomic, async, write_fault, writable);
 }
 
 pfn_t gfn_to_pfn_atomic(struct kvm *kvm, gfn_t gfn)
 {
-        return __gfn_to_pfn(kvm, gfn, true, NULL);
+        return __gfn_to_pfn(kvm, gfn, true, NULL, true, NULL);
 }
 EXPORT_SYMBOL_GPL(gfn_to_pfn_atomic);
 
-pfn_t gfn_to_pfn_async(struct kvm *kvm, gfn_t gfn, bool *async)
+pfn_t gfn_to_pfn_async(struct kvm *kvm, gfn_t gfn, bool *async,
+                       bool write_fault, bool *writable)
 {
-        return __gfn_to_pfn(kvm, gfn, false, async);
+        return __gfn_to_pfn(kvm, gfn, false, async, write_fault, writable);
 }
 EXPORT_SYMBOL_GPL(gfn_to_pfn_async);
 
 pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn)
 {
-        return __gfn_to_pfn(kvm, gfn, false, NULL);
+        return __gfn_to_pfn(kvm, gfn, false, NULL, true, NULL);
 }
 EXPORT_SYMBOL_GPL(gfn_to_pfn);
 
+pfn_t gfn_to_pfn_prot(struct kvm *kvm, gfn_t gfn, bool write_fault,
+                      bool *writable)
+{
+        return __gfn_to_pfn(kvm, gfn, false, NULL, write_fault, writable);
+}
+EXPORT_SYMBOL_GPL(gfn_to_pfn_prot);
+
 pfn_t gfn_to_pfn_memslot(struct kvm *kvm,
                          struct kvm_memory_slot *slot, gfn_t gfn)
 {
         unsigned long addr = gfn_to_hva_memslot(slot, gfn);
-        return hva_to_pfn(kvm, addr, false, NULL);
+        return hva_to_pfn(kvm, addr, false, NULL, true, NULL);
 }
 
 int gfn_to_page_many_atomic(struct kvm *kvm, gfn_t gfn, struct page **pages,