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Message-ID: <8d09dc2e-2d2d-e5f6-8cc7-eecfc94a17b2@linux.ibm.com>
Date:   Wed, 19 Jan 2022 13:46:43 +0100
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Subject: Re: [RFC PATCH v1 06/10] KVM: s390: Add vm IOCTL for key checked
 guest absolute memory access
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To:     Thomas Huth <thuth@redhat.com>,
        Janis Schoetterl-Glausch <scgl@linux.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>
Cc:     David Hildenbrand <david@redhat.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        kvm@vger.kernel.org, linux-s390@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20220118095210.1651483-1-scgl@linux.ibm.com>
 <20220118095210.1651483-7-scgl@linux.ibm.com>
 <a3a143f8-8fd5-49bf-9b2b-2f7cb04732de@redhat.com>
From:   Christian Borntraeger <borntraeger@linux.ibm.com>
In-Reply-To: <a3a143f8-8fd5-49bf-9b2b-2f7cb04732de@redhat.com>
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Am 19.01.22 um 12:52 schrieb Thomas Huth:
> On 18/01/2022 10.52, Janis Schoetterl-Glausch wrote:
>> Channel I/O honors storage keys and is performed on absolute memory.
>> For I/O emulation user space therefore needs to be able to do key
>> checked accesses.
> 
> Can't we do the checking in userspace? We already have functions for handling the storage keys there (see hw/s390x/s390-skeys-kvm.c), so why can't we do the checking in QEMU?

That would separate the key check from the memory operation. Potentially for a long time.
Wenn we piggy back on access_guest_abs_with_key we use mvcos in the host and thus do the key check in lockstep with the keycheck which is the preferrable solution.

I would also like to avoid reading guest storage keys via the ioctl that was done for migration in the I/O path just to do a single key check. This has peformance concerns.