linux-kernel - Re: [PATCH 4/6] s390: add system call to run tasks with modified branch prediction

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Message-ID: <299df1a8-f78d-15be-7217-6f201ea849c7@redhat.com>
Date:   Wed, 17 Jan 2018 12:50:21 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>,
        Florian Weimer <fweimer@...hat.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Heiko Carstens <heiko.carstens@...ibm.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jon Masters <jcm@...hat.com>,
        Marcus Meissner <meissner@...e.de>,
        Jiri Kosina <jkosina@...e.cz>
Subject: Re: [PATCH 4/6] s390: add system call to run tasks with modified
 branch prediction

On 17/01/2018 12:14, Christian Borntraeger wrote:
> 
> 
> On 01/17/2018 11:03 AM, Florian Weimer wrote:
>> On 01/17/2018 10:48 AM, Martin Schwidefsky wrote:
>>>          rc = syscall(__NR_s390_modify_bp);
>>>          if (rc) {
>>>                  perror("s390_modify_bp");
>>>                  exit(EXIT_FAILURE);
>>>          }
>>
>> Isn't this traditionally done through personality or prctl?
> 
> I think we want this per thread (and not per process). So I assume personality
> will not work out. Can a prctl be done per thread?

Yes, prctls can be either per-process (e.g. PR_SET_CHILD_SUBREAPER or
PR_SET_DUMPABLE) or per-thread (e.g. PR_SET_NAME or PR_SET_SECCOMP).

Paolo