linux-kernel - Re: [PATCH v2 3/3] rseq: optimise rseq_get_rseq_cs() and clear_rseq

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Date:   Tue, 13 Apr 2021 20:22:08 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        paulmck <paulmck@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
        Arjun Roy <arjunroy@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/3] rseq: optimise rseq_get_rseq_cs() and clear_rseq_cs()

On Tue, Apr 13, 2021 at 8:00 PM Mathieu Desnoyers
<mathieu.desnoyers@...icios.com> wrote:
>

> As long as the ifdefs are localized within clearly identified wrappers in the
> rseq code I don't mind doing the special-casing there.
>
> The point which remains is that I don't think we want to optimize for speed
> on 32-bit architectures when it adds special-casing and complexity to the 32-bit
> build. I suspect there is less and less testing performed on 32-bit architectures
> nowadays, and it's good that as much code as possible is shared between 32-bit and
> 64-bit builds to share the test coverage.
>

Quite frankly V1 was fine, I can't really make it looking better.

> Thanks,
>
> Mathieu
>
> >
> >
> >>
> >> Thanks,
> >>
> >> Mathieu
> >>
> >> >
> >> > diff --git a/kernel/rseq.c b/kernel/rseq.c
> >> > index
> >> > f2eee3f7f5d330688c81cb2e57d47ca6b843873e..537b1f684efa11069990018ffa3642c209993011
> >> > 100644
> >> > --- a/kernel/rseq.c
> >> > +++ b/kernel/rseq.c
> >> > @@ -136,6 +136,10 @@ static int rseq_get_cs_ptr(struct rseq_cs __user **uptrp,
> >> > {
> >> >        u32 ptr;
> >> >
> >> > +       if (get_user(ptr, &rseq->rseq_cs.ptr.padding))
> >> > +               return -EFAULT;
> >> > +       if (ptr)
> >> > +               return -EINVAL;
> >> >        if (get_user(ptr, &rseq->rseq_cs.ptr.ptr32))
> >> >                return -EFAULT;
> >> >        *uptrp = (struct rseq_cs __user *)ptr;
> >> > @@ -150,8 +154,9 @@ static int rseq_get_rseq_cs(struct task_struct *t,
> >> > struct rseq_cs *rseq_cs)
> >> >        u32 sig;
> >> >        int ret;
> >> >
> >> > -       if (rseq_get_cs_ptr(&urseq_cs, t->rseq))
> >> > -               return -EFAULT;
> >> > +       ret = rseq_get_cs_ptr(&urseq_cs, t->rseq);
> >> > +       if (ret)
> >> > +               return ret;
> >> >        if (!urseq_cs) {
> >> >                memset(rseq_cs, 0, sizeof(*rseq_cs));
> >> >                return 0;
> >> > @@ -237,7 +242,8 @@ static int clear_rseq_cs(struct task_struct *t)
> >> > #ifdef CONFIG_64BIT
> >> >        return put_user(0UL, &t->rseq->rseq_cs.ptr64);
> >> > #else
> >> > -       return put_user(0UL, &t->rseq->rseq_cs.ptr.ptr32);
> >> > +       return put_user(0UL, &t->rseq->rseq_cs.ptr.ptr32) |
> >> > +              put_user(0UL, &t->rseq->rseq_cs.ptr.padding);
> >> > #endif
> >> >  }
> >>
> >> --
> >> Mathieu Desnoyers
> >> EfficiOS Inc.
> > > http://www.efficios.com
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com