linux-kernel - Re: [PATCH 1/2] KVM: s390: Don't indicate suppression on dirtying, failing memop

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Message-ID: <6f385869-3f3b-d985-6804-02943a8dee07@linux.ibm.com>
Date:   Fri, 1 Apr 2022 19:40:30 +0200
From:   Janis Schoetterl-Glausch <scgl@...ux.ibm.com>
To:     Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH 1/2] KVM: s390: Don't indicate suppression on dirtying,
 failing memop

On 4/1/22 19:13, Christian Borntraeger wrote:
> 
> 
> Am 01.04.22 um 19:02 schrieb Janis Schoetterl-Glausch:
>> If user space uses a memop to emulate an instruction and that
>> memop fails, the execution of the instruction ends.
>> Instruction execution can end in different ways, one of which is
>> suppression, which requires that the instruction execute like a no-op.
>> A writing memop that spans multiple pages and fails due to key
>> protection can modified guest memory. Therefore do not indicate a
>> suppressing instruction ending in this case.

A writing memop that spans multiple pages and fails due to key
protection can modified guest memory, as a result, the likely
correct ending is termination. Therefore do not indicate a
suppressing instruction ending in this case.

?

It's phrased a bit vaguely, because we don't really know what user space wants
when emulating an instruction, I guess it could try to revert the changes?
And the TEID does not indicate termination, it only indicates that
the guest cannot assume that the instruction was suppressed.

> 
> Make it explicit in the changelog that this is "terminating" instead of
> "suppressing". z/VM has the same logic and the architecture allows for
> terminating in those cases (even for ESOP2).
>  >
>> Signed-off-by: Janis Schoetterl-Glausch <scgl@...ux.ibm.com>
>> ---