linux-kernel - Re: [RFC PATCH v1 06/10] KVM: s390: Add vm IOCTL for key checked guest absolute memory access

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Date:   Wed, 19 Jan 2022 13:53:35 +0100
From:   Thomas Huth <thuth@...hat.com>
To:     Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janis Schoetterl-Glausch <scgl@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        kvm@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 06/10] KVM: s390: Add vm IOCTL for key checked
 guest absolute memory access

On 19/01/2022 13.46, Christian Borntraeger wrote:
> 
> 
> 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.

Ok, makes sense - Janis, could you please add this rationale to the patch 
description?

  Thomas