linux-kernel - Re: [PATCH v5 14/18] kvm: i8254: Deactivate APICv when using in-kernel PIT re-injection mode.

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Date:   Fri, 21 Feb 2020 09:27:29 +0700
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        pbonzini@...hat.com, joro@...tes.org, vkuznets@...hat.com,
        rkagan@...tuozzo.com, graf@...zon.com, jschoenh@...zon.de,
        karahmed@...zon.de, rimasluk@...zon.com, jon.grimm@....com
Subject: Re: [PATCH v5 14/18] kvm: i8254: Deactivate APICv when using
 in-kernel PIT re-injection mode.

Alex,

On 2/19/20 1:51 AM, Alex Williamson wrote:
> On Thu, 14 Nov 2019 14:15:16 -0600
> Suravee Suthikulpanit <suravee.suthikulpanit@....com> wrote:
> 
>> AMD SVM AVIC accelerates EOI write and does not trap. This causes
>> in-kernel PIT re-injection mode to fail since it relies on irq-ack
>> notifier mechanism. So, APICv is activated only when in-kernel PIT
>> is in discard mode e.g. w/ qemu option:
>>
>>    -global kvm-pit.lost_tick_policy=discard
>>
>> Also, introduce APICV_INHIBIT_REASON_PIT_REINJ bit to be used for this
>> reason.
>>
>> Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
>> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
>> ---
> 
> Hi,
> 
> I've bisected https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.kernel.org%2Fshow_bug.cgi%3Fid%3D206579&amp;data=02%7C01%7Csuravee.suthikulpanit%40amd.com%7C4d26019120374670e2ec08d7b4a39d9f%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637176487135073269&amp;sdata=Yp1ZSoOxVphXyd60gerlaJkOF67r65emQZ4zhc%2BLFy4%3D&amp;reserved=0 (a
> kernel NULL pointer deref when using device assigned on AMD platforms)
> to this commit, e2ed4078a6ef3ddf4063329298852e24c36d46c8.  My VM is a
> very basic libvirt managed domain with an assigned NIC, I don't even
> have an OS installed:

Thanks for the bisect information. I'm currently working on reproducing this issue. On your system are you enabling AVIC 
(e.g. modprobe kvm_amd avic=1)?

Suravee