From mboxrd@z Thu Jan  1 00:00:00 1970
From: Heiko Carstens <heiko.carstens@de.ibm.com>
Subject: Re: [PATCH 4/6] s390: add system call to run tasks with modified
 branch prediction
Date: Wed, 17 Jan 2018 14:25:49 +0100
Message-ID: <20180117132549.GC5708@osiris>
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Cc: Christian Borntraeger <borntraeger@de.ibm.com>,
        Florian Weimer <fweimer@redhat.com>,
        linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org,
        kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
        Cornelia Huck <cohuck@redhat.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jon Masters <jcm@redhat.com>,
        Marcus Meissner <meissner@suse.de>,
        Jiri Kosina <jkosina@suse.cz>
To: Martin Schwidefsky <schwidefsky@de.ibm.com>
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On Wed, Jan 17, 2018 at 12:55:06PM +0100, Martin Schwidefsky wrote:
> On Wed, 17 Jan 2018 12:14:52 +0100
> Christian Borntraeger <borntraeger@de.ibm.com> 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?
> 
> The prctl interface seems to be usable to set a per-thread control
> as well. But there is no architecture specific prctl as far as I
> can see. Maybe a common PR_SET_NOBP with an arch function like
> arch_set_nobp.

There is for example PR_MPX_ENABLE_MANAGEMENT, which is x86 specific. On
the other hand x86 even has an arch_prctl() system call... ;)