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From:   David Hildenbrand <david@redhat.com>
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Subject: Re: [PATCH v2 1/5] KVM: s390: vsie: Fix region 1 ASCE sanity shadow address checks
Date:   Fri, 3 Apr 2020 21:55:02 +0200
Message-Id: <67F45F4F-33CB-455A-8CB8-7D20D9A2BF2F@redhat.com>
References: <59b411eb-dabe-8cac-9270-7a9f0faa63d5@de.ibm.com>
Cc:     David Hildenbrand <david@redhat.com>, kvm@vger.kernel.org,
        linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        Vasily Gorbik <gor@linux.ibm.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Cornelia Huck <cohuck@redhat.com>,
        Janosch Frank <frankja@linux.ibm.com>, stable@vger.kernel.org
In-Reply-To: <59b411eb-dabe-8cac-9270-7a9f0faa63d5@de.ibm.com>
To:     Christian Borntraeger <borntraeger@de.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> Am 03.04.2020 um 19:56 schrieb Christian Borntraeger <borntraeger@de.ibm.c=
om>:
>=20
> =EF=BB=BF
>=20
>> On 03.04.20 17:30, David Hildenbrand wrote:
>> In case we have a region 1 ASCE, our shadow/g3 address can have any value=
.
>> Unfortunately, (-1UL << 64) is undefined and triggers sometimes,
>> rejecting valid shadow addresses when trying to walk our shadow table
>> hierarchy.
>=20
> I thin the range of the addresses do not matter.
> Took me a while to understand maybe rephrase that:
>=20
> In case we have a region 1 the following calculation=20
> (31 + ((gmap->asce & _ASCE_TYPE_MASK) >> 2)*11)
> results in 64. As shifts beyond the size are undefined the compiler is fre=
e to use
> instructions like sllg. sllg will only use 6 bits of the shift value (here=
 64)
> resulting in no shift at all. That means that ALL addresses will be reject=
ed.

Interestingly, it would not fail when shadowing the r2t, but only when tryin=
g to shadow the r3t.

>=20
> With that this makes sense.=20
>=20
> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
>=20

In case there are no other comments, can you fixup when applying, or do you w=
ant me to resend?

Cheers=