Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <cd79f893-c711-1a60-47d6-7c392e02fc6a@redhat.com>
Date:   Wed, 19 Jan 2022 13:53:35 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.4.0
Subject: Re: [RFC PATCH v1 06/10] KVM: s390: Add vm IOCTL for key checked
 guest absolute memory access
Content-Language: en-US
To:     Christian Borntraeger <borntraeger@linux.ibm.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>
 <8d09dc2e-2d2d-e5f6-8cc7-eecfc94a17b2@linux.ibm.com>
From:   Thomas Huth <thuth@redhat.com>
In-Reply-To: <8d09dc2e-2d2d-e5f6-8cc7-eecfc94a17b2@linux.ibm.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

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