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

[Wanpeng Li]

On Thu, Sep 18, 2014 at 09:13:26AM +0300, Gleb Natapov wrote:
>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.

Got it, thanks for your pointing out.

Reviewed-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxxxxxx>

Regards,
Wanpeng Li 

>
>> 	  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.
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