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

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Message-ID: <39c529db-e7bd-c216-62b7-773a51d919b6@linux.ibm.com>
Date:   Wed, 19 Jan 2022 14:17:43 +0100
From:   Janis Schoetterl-Glausch <scgl@...ux.ibm.com>
To:     Thomas Huth <thuth@...hat.com>,
        Christian Borntraeger <borntraeger@...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 1/19/22 13:53, Thomas Huth wrote:
> 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?

Will do.
> 
>  Thomas
>