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

Gleb Natapov
2014-09-18T06:13:26Z

On Thu, Sep 18, 2014 at 08:29:17AM +0800, Wanpeng Li wrote:
> 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
*async = false

> __gfn_to_pfn_memslot
> hva_to_pfn
> hva_to_pfn_fast
> hva_to_pfn_slow
hva_to_pfn_slow checks async not *async.

> 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
> >
> >--
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--
Gleb.