linux-kernel - Re: [PATCH v1 1/1] KVM: s390/mm: Properly reset no-dat

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Date:   Thu, 9 Nov 2023 14:11:48 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Claudio Imbrenda <imbrenda@...ux.ibm.com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        frankja@...ux.ibm.com, nrb@...ux.ibm.com, nsg@...ux.ibm.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com, svens@...ux.ibm.com,
        agordeev@...ux.ibm.com,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
Subject: Re: [PATCH v1 1/1] KVM: s390/mm: Properly reset no-dat

Am 09.11.23 um 13:36 schrieb Claudio Imbrenda:
> When the CMMA state needs to be reset, the no-dat bit also needs to be
> reset. Failure to do so could cause issues in the guest, since the
> guest expects the bit to be cleared after a reset.

This happens during reset of a guest (or whenever QEMU calls the CLR_CMMA thingi).
I think after reset a normal Linux guest has no DAT tables and very likely
a cpu reset (with explicit full guest flush) will happen. It will very likely
also set the CMMA state during boot before setting up its DAT tables.
So for the normal reboot this should be ok. But I can imagine cases that would
not be ok. So maybe add cc stable?