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

[Wanpeng Li]

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 majord...@kvack.org.  For more info on Linux MM,
>see: http://www.linux-mm.org/ .
>Don't email: <a href=mailto:"d...@kvack.org";> em...@kvack.org </a>
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html