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Subject: Re: [PATCH] KVM: arm/arm64: vgic-its: Check hopefully the last
 DISCARD command error
To:     Auger Eric <eric.auger@redhat.com>, <maz@kernel.org>
CC:     <andre.przywara@arm.com>, <linux-arm-kernel@lists.infradead.org>,
        <kvmarm@lists.cs.columbia.edu>, <linux-kernel@vger.kernel.org>,
        <wanghaibin.wang@huawei.com>
References: <20191225133014.1825-1-yuzenghui@huawei.com>
 <f9997198-c990-d638-24d0-41d6280a9d8a@redhat.com>
From:   Zenghui Yu <yuzenghui@huawei.com>
Message-ID: <41c88abb-433a-f87c-c858-7f2eb4c40926@huawei.com>
Date:   Tue, 14 Jan 2020 15:10:16 +0800
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Hi Eric,

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:
>>
>>   - [ ... (those which we have already handled) ]
> nit: I would remove the above and simply say the discard is supposed to
> fail if the collection is not mapped to any target redistributor. If an
> ITE exists then the ite->collection is non NULL.

I think this is not always true. Let's talk about the following scenario
(a bit insane, though):

1. First map a LPI to an unmapped Collection, then ite->collection is
    non NULL and its target_addr is COLLECTION_NOT_MAPPED.

2. Then issue MAPC and unMAPC(V=0) commands on this Collection, the
    ite->collection will be NULL, see vgic_its_free_collection().

Discard the LPI mapping after "1" or "2", we will both encounter the
unmapped collection command error.

> 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?

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 != ite->collection'.
We can safely get rid of it.

> 
> Reviewed-by: Eric Auger <eric.auger@redhat.com>
> 

Thanks for that. I'll change the commit message with your suggestion and
add your R-b in v2.


Thanks,
Zenghui