KVM: Enable async page fault processing

If asynchronous hva_to_pfn() is requested call GUP with FOLL_NOWAIT to
avoid sleeping on IO. Check for hwpoison is done at the same time,
otherwise check_user_page_hwpoison() will call GUP again and will put
vcpu to sleep.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 21 insertions, 2 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 556e3efe5325..6330653480e4 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1037,6 +1037,17 @@ static pfn_t get_fault_pfn(void)
         return fault_pfn;
 }
 
+int get_user_page_nowait(struct task_struct *tsk, struct mm_struct *mm,
+        unsigned long start, int write, struct page **page)
+{
+        int flags = FOLL_TOUCH | FOLL_NOWAIT | FOLL_HWPOISON | FOLL_GET;
+
+        if (write)
+                flags |= FOLL_WRITE;
+
+        return __get_user_pages(tsk, mm, start, 1, flags, page, NULL, NULL);
+}
+
 static inline int check_user_page_hwpoison(unsigned long addr)
 {
         int rc, flags = FOLL_TOUCH | FOLL_HWPOISON | FOLL_WRITE;
@@ -1070,7 +1081,14 @@ static pfn_t hva_to_pfn(struct kvm *kvm, unsigned long addr, bool atomic,
                 if (writable)
                         *writable = write_fault;
 
-                npages = get_user_pages_fast(addr, 1, write_fault, page);
+                if (async) {
+                        down_read(&current->mm->mmap_sem);
+                        npages = get_user_page_nowait(current, current->mm,
+                                                     addr, write_fault, page);
+                        up_read(&current->mm->mmap_sem);
+                } else
+                        npages = get_user_pages_fast(addr, 1, write_fault,
+                                                     page);
 
                 /* map read fault as writable if possible */
                 if (unlikely(!write_fault) && npages == 1) {
@@ -1093,7 +1111,8 @@ static pfn_t hva_to_pfn(struct kvm *kvm, unsigned long addr, bool atomic,
                         return get_fault_pfn();
 
                 down_read(&current->mm->mmap_sem);
-                if (check_user_page_hwpoison(addr)) {
+                if (npages == -EHWPOISON ||
+                        (!async && check_user_page_hwpoison(addr))) {
                         up_read(&current->mm->mmap_sem);
                         get_page(hwpoison_page);
                         return page_to_pfn(hwpoison_page);