Re: [PATCH v1 6/7] kvm/x86: Hyper-V SynIC message slot pending clearing at SINT ack

[Andrey Smetanin <asmetanin@virtuozzo.com>]

On 11/26/2015 05:43 PM, Paolo Bonzini wrote:
>
>
> On 26/11/2015 10:06, Andrey Smetanin wrote:
>>
>>
>> On 11/25/2015 08:14 PM, Paolo Bonzini wrote:
>>>
>>>
>>> On 25/11/2015 17:55, Andrey Smetanin wrote:
>>>>>
>>>>> +    gpa = synic->msg_page & PAGE_MASK;
>>>>> +    page = kvm_vcpu_gfn_to_page(vcpu, gpa >> PAGE_SHIFT);
>>>>> +    if (is_error_page(page)) {
>>>>> +        vcpu_err(vcpu, "Hyper-V SynIC can't get msg page, gpa
>>>>> 0x%llx\n",
>>>>> +             gpa);
>>>>> +        return;
>>>>> +    }
>>>>> +    msg_page = kmap_atomic(page);
>>>>
>>>> But the message page is not being pinned, is it?
>>>>
>>>> Actually I don't know anything about pinning.
>>>> Is it pinning against page swapping ?
>>>
>>> Yes.  Unless the page is pinned, kmap_atomic can fail.
>> kmap_atomic() can't fail for a valid page struct. Does
>> kvm_vcpu_gfn_to_page() can provide invalid page(swapped page) struct
>> which may pass is_error_page(page) check but can leads to incorrect
>> behavior inside kmap_atomic()?
>
> No, you're right.  Nevermind, I was confused because I thought you
> needed kmap_atomic rather than kmap.  Here using kmap_atomic is just an
> optimization, so it's okay.  (If you needed kmap_atomic, the problem
> would have been that kvm_vcpu_gfn_to_page() can sleep).
>
> In patch 7/7 you're also not in atomic context, so kvm_vcpu_gfn_to_page
> is okay.
>
> Shouldn't have reviewed the patch when tired. :)
>
> Then the patches look good, I think.  With a testcase I can try them out
> and hopefully merge them for Linux 4.5 / QEMU 2.6.
Thank you!

We already have a working Hyper-V SynIC timers kvm-unit-tests test case.
We are going to send appropriate patches seria into kvm-unit-tests git.

But  kvm-unit-tests master now broken:
 > make
objcopy -O elf32-i386 x86/memory.elf x86/memory.flat
make: *** No rule to make target 'x86/pku.o', needed by 'x86/pku.elf'. 
Stop.

The problem is in latest commit 3da70799dd3cf1169c4668b4a3fd6f598528b8b9.

The commit adds 'pku' test case building, but not added any pku.c 
implementation file.

[root@asm-pc kvm-unit-tests]# ls -al x86/pku.c
ls: cannot access x86/pku.c: No such file or directory


Could you please fix it ?
>
> Paolo
>