hva_to_pfn_fast() currently just fails for faults where establishing
writable mappings is forbidden, which is unnecessary. Instead, try
getting the page without passing FOLL_WRITE. This allows the
aforementioned faults to (potentially) be resolved without falling back
to slow GUP.
Suggested-by: James Houghton <jthoughton@xxxxxxxxxx>
Signed-off-by: Anish Moorthy <amoorthy@xxxxxxxxxx>
---
virt/kvm/kvm_main.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 13aa2ed11d0d..a7e6320dd7f0 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2508,7 +2508,7 @@ static inline int check_user_page_hwpoison(unsigned long addr)
}
/*
- * The fast path to get the writable pfn which will be stored in @pfn,
+ * The fast path to get the pfn which will be stored in @pfn,
* true indicates success, otherwise false is returned. It's also the
* only part that runs if we can in atomic context.
*/
@@ -2522,10 +2522,9 @@ static bool hva_to_pfn_fast(unsigned long addr, bool write_fault,
* or the caller allows to map a writable pfn for a read fault
* request.
*/
- if (!(write_fault || writable))
- return false;
+ unsigned int gup_flags = (write_fault || writable) ? FOLL_WRITE : 0;
- if (get_user_page_fast_only(addr, FOLL_WRITE, page)) {
+ if (get_user_page_fast_only(addr, gup_flags, page)) {
*pfn = page_to_pfn(page[0]);
if (writable)
--
2.42.0.283.g2d96d420d3-goog
