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

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Message-Id: <20180117125506.26f3813c@mschwideX1>
Date:   Wed, 17 Jan 2018 12:55:06 +0100
From:   Martin Schwidefsky <schwidefsky@...ibm.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>
Cc:     Florian Weimer <fweimer@...hat.com>, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, kvm@...r.kernel.org,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Paolo Bonzini <pbonzini@...hat.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 Wed, 17 Jan 2018 12:14:52 +0100
Christian Borntraeger <borntraeger@...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.

> > 
> > This looks like something other architectures may want as well.  

Yes, that is likely.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.