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.
Paolo
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