linux-kernel - Re: [PATCH v6 12/14] KVM: s390: Extend MEM_OP ioctl by storage key checked cmpxchg

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Message-ID: <Y9I3liGZJhNtt1N5@osiris>
Date:   Thu, 26 Jan 2023 09:19:34 +0100
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Janis Schoetterl-Glausch <scgl@...ux.ibm.com>
Cc:     Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Jonathan Corbet <corbet@....net>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-s390@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        Sven Schnelle <svens@...ux.ibm.com>
Subject: Re: [PATCH v6 12/14] KVM: s390: Extend MEM_OP ioctl by storage key
 checked cmpxchg

On Wed, Jan 25, 2023 at 10:26:06PM +0100, Janis Schoetterl-Glausch wrote:
> User space can use the MEM_OP ioctl to make storage key checked reads
> and writes to the guest, however, it has no way of performing atomic,
> key checked, accesses to the guest.
> Extend the MEM_OP ioctl in order to allow for this, by adding a cmpxchg
> op. For now, support this op for absolute accesses only.
> 
> This op can be use, for example, to set the device-state-change
> indicator and the adapter-local-summary indicator atomically.
> 
> Signed-off-by: Janis Schoetterl-Glausch <scgl@...ux.ibm.com>
> ---
>  include/uapi/linux/kvm.h |   8 +++
>  arch/s390/kvm/gaccess.h  |   3 ++
>  arch/s390/kvm/gaccess.c  | 103 +++++++++++++++++++++++++++++++++++++++
>  arch/s390/kvm/kvm-s390.c |  56 ++++++++++++++++++++-
>  4 files changed, 169 insertions(+), 1 deletion(-)
...
> +		ret = cmpxchg_user_key((u8 *)hva, &old, *old_addr, new, access_key);

FWIW, this and the three others need a __user annotation:

		ret = cmpxchg_user_key((u8 __user *)hva, &old, *old_addr, new, access_key);

Otherwise you end up with sparse warnings (compile with C=1).