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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Wed, 25 Nov 2015 18:14:43 +0100
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Subject: Re: [Qemu-devel] [PATCH v1 6/7] kvm/x86: Hyper-V SynIC message slot
 pending clearing at SINT ack
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To: asmetanin@virtuozzo.com, kvm@vger.kernel.org
Cc: Gleb Natapov <gleb@kernel.org>, Haiyang Zhang <haiyangz@microsoft.com>, qemu-devel@nongnu.org, Roman Kagan <rkagan@virtuozzo.com>, "Denis V. Lunev" <den@openvz.org>, Vitaly Kuznetsov <vkuznets@redhat.com>, "K. Y. Srinivasan" <kys@microsoft.com>



On 25/11/2015 17:55, Andrey Smetanin wrote:
>>
>> +    gpa =3D synic->msg_page & PAGE_MASK;
>> +    page =3D 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 =3D 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.

However, I don't think that kvm_hv_notify_acked_sint is called from
atomic context.  It is only called from apic_set_eoi.  Could you just
use kvm_vcpu_write_guest_page?

By the way, do you need to do this also in kvm_get_apic_interrupt, for
auto EOI interrupts?

Thanks,

Paolo

> Could you please clarify and provide an API to use in this case ?