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Subject: Re: [PATCH 2/2] xen-pciback: prepare for the split for stub and PV
To:     Oleksandr Andrushchenko <Oleksandr_Andrushchenko@epam.com>,
        Stefano Stabellini <sstabellini@kernel.org>
Cc:     "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "boris.ostrovsky@oracle.com" <boris.ostrovsky@oracle.com>,
        "julien@xen.org" <julien@xen.org>,
        "jbeulich@suse.com" <jbeulich@suse.com>,
        Oleksandr Andrushchenko <andr2000@gmail.com>
References: <20210922101422.2319240-1-andr2000@gmail.com>
 <20210922101422.2319240-2-andr2000@gmail.com>
 <alpine.DEB.2.21.2109221407350.17979@sstabellini-ThinkPad-T480s>
 <4552e4b6-21a8-4829-16b4-7cda8ba0c0d1@epam.com>
From:   Juergen Gross <jgross@suse.com>
Message-ID: <7880dee9-7372-5a25-db55-018f21e8b08c@suse.com>
Date:   Thu, 23 Sep 2021 11:05:03 +0200
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From: Juergen Gross <jgross@suse.com>
To: Oleksandr Andrushchenko <Oleksandr_Andrushchenko@epam.com>,
 Stefano Stabellini <sstabellini@kernel.org>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
 "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
 "boris.ostrovsky@oracle.com" <boris.ostrovsky@oracle.com>,
 "julien@xen.org" <julien@xen.org>, "jbeulich@suse.com" <jbeulich@suse.com>,
 Oleksandr Andrushchenko <andr2000@gmail.com>
Message-ID: <7880dee9-7372-5a25-db55-018f21e8b08c@suse.com>
Subject: Re: [PATCH 2/2] xen-pciback: prepare for the split for stub and PV
References: <20210922101422.2319240-1-andr2000@gmail.com>
 <20210922101422.2319240-2-andr2000@gmail.com>
 <alpine.DEB.2.21.2109221407350.17979@sstabellini-ThinkPad-T480s>
 <4552e4b6-21a8-4829-16b4-7cda8ba0c0d1@epam.com>
In-Reply-To: <4552e4b6-21a8-4829-16b4-7cda8ba0c0d1@epam.com>

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On 23.09.21 11:02, Oleksandr Andrushchenko wrote:
>=20
> On 23.09.21 00:10, Stefano Stabellini wrote:
>> On Wed, 22 Sep 2021, Oleksandr Andrushchenko wrote:
>>> --- a/drivers/xen/xen-pciback/xenbus.c
>>> +++ b/drivers/xen/xen-pciback/xenbus.c
>>> @@ -743,6 +743,9 @@ const struct xen_pcibk_backend *__read_mostly xen=
_pcibk_backend;
>>>   =20
>>>    int __init xen_pcibk_xenbus_register(void)
>>>    {
>>> +	if (!xen_pcibk_pv_support())
>>> +		return 0;
>> Is this truly enough to stop the PV backend from initializing? Have yo=
u
>> actually tested it to make sure? If it works, amazing! I am quite happ=
y
>> about this approach :-)
>=20
> Well, I put some logs into the driver and saw nothing obvious pointing
>=20
> to any backend activities (probably this is also because I don't have a=
ny
>=20
> frontend). I see that the xenbus driver is not registered. In XenStore =
I see:
>=20
> root@dom0:~# xenstore-ls -f | grep pci
> /local/domain/0/backend/pci =3D ""
> /local/domain/0/backend/pci/2 =3D ""
> /local/domain/0/backend/pci/2/0 =3D ""
> /local/domain/0/backend/pci/2/0/frontend =3D "/local/domain/2/device/pc=
i/0"
> /local/domain/0/backend/pci/2/0/frontend-id =3D "2"
> /local/domain/0/backend/pci/2/0/online =3D "1"
> /local/domain/0/backend/pci/2/0/state =3D "1"
> /local/domain/0/backend/pci/2/0/domain =3D "DomU"
> /local/domain/0/backend/pci/2/0/key-0 =3D "0000:03:00.0"
> /local/domain/0/backend/pci/2/0/dev-0 =3D "0000:03:00.0"
> /local/domain/0/backend/pci/2/0/opts-0 =3D "msitranslate=3D0,power_mgmt=
=3D0,permissive=3D0,rdm_policy=3Dstrict"
> /local/domain/0/backend/pci/2/0/state-0 =3D "1"
> /local/domain/0/backend/pci/2/0/num_devs =3D "1"
> /local/domain/2/device/pci =3D ""
> /local/domain/2/device/pci/0 =3D ""
> /local/domain/2/device/pci/0/backend =3D "/local/domain/0/backend/pci/2=
/0"
> /local/domain/2/device/pci/0/backend-id =3D "0"
> /local/domain/2/device/pci/0/state =3D "1"
> /libxl/pci =3D ""
> /libxl/pci/0000-03-00-0 =3D ""
> /libxl/pci/0000-03-00-0/domid =3D "2"
>=20
> But IIUIC these come from the toolstack
>=20
> @Juergen, do you know how to check if the backend is indeed not running=

>=20
> or the above should be enough to prove?

I don't see how the backend could be running without being registered
with xenbus. It won't receive any watches, so there is no way a
connection with a frontend could be established.


Juergen


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