KVM: use 'writable' as a hint to map writable pfn
In current code, we always map writable pfn for the read fault, in order
to support readonly memslot, we map writable pfn only if 'writable'
is not NULL
Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index aa4a38a..c89d1b5 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1054,6 +1054,14 @@
if (!(async || atomic))
return false;
+ /*
+ * Fast pin a writable pfn only if it is a write fault request
+ * or the caller allows to map a writable pfn for a read fault
+ * request.
+ */
+ if (!(write_fault || writable))
+ return false;
+
npages = __get_user_pages_fast(addr, 1, 1, page);
if (npages == 1) {
*pfn = page_to_pfn(page[0]);
@@ -1093,7 +1101,7 @@
return npages;
/* map read fault as writable if possible */
- if (unlikely(!write_fault)) {
+ if (unlikely(!write_fault) && writable) {
struct page *wpage[1];
npages = __get_user_pages_fast(addr, 1, 1, wpage);
@@ -1109,6 +1117,20 @@
return npages;
}
+/*
+ * Pin guest page in memory and return its pfn.
+ * @addr: host virtual address which maps memory to the guest
+ * @atomic: whether this function can sleep
+ * @async: whether this function need to wait IO complete if the
+ * host page is not in the memory
+ * @write_fault: whether we should get a writable host page
+ * @writable: whether it allows to map a writable host page for !@write_fault
+ *
+ * The function will map a writable host page for these two cases:
+ * 1): @write_fault = true
+ * 2): @write_fault = false && @writable, @writable will tell the caller
+ * whether the mapping is writable.
+ */
static pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
bool write_fault, bool *writable)
{