Re: [PATCH v2] kvm: Faults which trigger IO release the mmap_sem

Wanpeng Li
2014-09-18T00:29:17Z

Hi Andres,
On Wed, Sep 17, 2014 at 10:51:48AM -0700, Andres Lagar-Cavilla wrote:
[...]
> static inline int check_user_page_hwpoison(unsigned long addr)
> {
> int rc, flags = FOLL_TOUCH | FOLL_HWPOISON | FOLL_WRITE;
>@@ -1177,9 +1214,15 @@ static int hva_to_pfn_slow(unsigned long addr, bool *async, bool write_fault,
> 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);
>+ } else {
>+ /*
>+ * By now we have tried gup_fast, and possibly async_pf, and we
>+ * are certainly not atomic. Time to retry the gup, allowing
>+ * mmap semaphore to be relinquished in the case of IO.
>+ */
>+ npages = kvm_get_user_page_io(current, current->mm, addr,
>+ write_fault, page);
>+ }

try_async_pf
gfn_to_pfn_async
__gfn_to_pfn async = false
__gfn_to_pfn_memslot
hva_to_pfn
hva_to_pfn_fast
hva_to_pfn_slow
kvm_get_user_page_io

page will always be ready after kvm_get_user_page_io which leads to APF
don't need to work any more.

Regards,
Wanpeng Li

> if (npages != 1)
> return npages;
>
>--
>2.1.0.rc2.206.gedb03e5
>
>--
>To unsubscribe, send a message with 'unsubscribe linux-mm' in
>the body to majordomo@kvack.org. For more info on Linux MM,
>see: http://www.linux-mm.org/ .
>Don't email: email@kvack.org