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Subject: Re: [PATCH] KVM: arm/arm64: vgic-its: Check hopefully the last
 DISCARD command error
To:     Zenghui Yu <yuzenghui@huawei.com>, maz@kernel.org
Cc:     andre.przywara@arm.com, wanghaibin.wang@huawei.com,
        kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org
References: <20191225133014.1825-1-yuzenghui@huawei.com>
 <f9997198-c990-d638-24d0-41d6280a9d8a@redhat.com>
 <41c88abb-433a-f87c-c858-7f2eb4c40926@huawei.com>
From:   Auger Eric <eric.auger@redhat.com>
Message-ID: <615c4713-d00e-e2f7-c2d4-fa8047355c9b@redhat.com>
Date:   Tue, 14 Jan 2020 09:20:50 +0100
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Hi Zenghui,

On 1/14/20 8:10 AM, Zenghui Yu wrote:
> Hi Eric,
>=20
> On 2020/1/10 16:37, Auger Eric wrote:
>> Hi Zenghui,
>>
>> On 12/25/19 2:30 PM, Zenghui Yu wrote:
>>> DISCARD command error occurs if any of the following apply:
>>>
>>> =C2=A0 - [ ... (those which we have already handled) ]
>> nit: I would remove the above and simply say the discard is supposed t=
o
>> fail if the collection is not mapped to any target redistributor. If a=
n
>> ITE exists then the ite->collection is non NULL.
>=20
> I think this is not always true. Let's talk about the following scenari=
o
> (a bit insane, though):
>=20
> 1. First map a LPI to an unmapped Collection, then ite->collection is
> =C2=A0=C2=A0 non NULL and its target_addr is COLLECTION_NOT_MAPPED.
>=20
> 2. Then issue MAPC and unMAPC(V=3D0) commands on this Collection, the
> =C2=A0=C2=A0 ite->collection will be NULL, see vgic_its_free_collection=
().
You're right I missed that case.
>=20
> Discard the LPI mapping after "1" or "2", we will both encounter the
> unmapped collection command error.
>=20
>> What needs to be checked is its_is_collection_mapped().
>>
>> By the way update_affinity_collection() also tests ite->collection. I
>> think this is useless or do I miss something?
>=20
> Yeah, I agree. We managed to invoke update_affinity_collection(,, coll)=
,
> ensure that the 'coll' can _not_ be NULL.
> So '!ite->collection' is already a subcase of 'coll !=3D ite->collectio=
n'.
> We can safely get rid of it.
OK. But that's not for the (wrong) reason I mentioned above. So it is a
minor cleanup and you may just leave it as is and just focus on this fix.

Thanks

Eric
>=20
>>
>> Reviewed-by: Eric Auger <eric.auger@redhat.com>
>>
>=20
> Thanks for that. I'll change the commit message with your suggestion an=
d
> add your R-b in v2.
>=20
>=20
> Thanks,
> Zenghui
>=20
>=20
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>=20