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Re: [PATCH] target/s390x/tcg: SPX: check validity of new prefix

From: David Hildenbrand
Subject: Re: [PATCH] target/s390x/tcg: SPX: check validity of new prefix
Date: Mon, 27 Jun 2022 19:10:46 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0

On 27.06.22 19:06, Janis Schoetterl-Glausch wrote:
> On 6/27/22 18:27, David Hildenbrand wrote:
>> On 27.06.22 15:12, Janis Schoetterl-Glausch wrote:
>>> According to the architecture, SET PREFIX must try to access the new
>>> prefix area and recognize an addressing exception if the area is not
>>> accessible.
>>> For qemu this check prevents a crash in cpu_map_lowcore after an
>>> inaccessible prefix area has been set.
>> I don't think that's possible. Our memory increments are 1 MiB and one
>> would have to cross a 1~MiB range with the second page to trigger that.
>> IIRC that's impossible with SPX address alignment requirements?
> Are you saying that checking the first page is sufficient?

Yes, unless I'm wrong. :)

/* Due to alignment and QEMU memory sizes, it's sufficient to check the
first page only. */

> I'm not sure that this the case for the architecture in general,
> but I guess it is true for tcg. Do you want me to remove the second check?

Should have been clearer (and I somehow thought we'd be checking the
first page already :))

Reviewed-by: David Hildenbrand <david@redhat.com>


David / dhildenb

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