linux-kernel - Re: [PATCH RFC V3 5/9] x86/pks: Add PKS kernel API

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Date:   Fri, 16 Oct 2020 22:42:16 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Fenghua Yu <fenghua.yu@...el.com>, x86@...nel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH RFC V3 5/9] x86/pks: Add PKS kernel API

On Fri, Oct 16, 2020 at 01:07:47PM +0200, Peter Zijlstra wrote:
> On Fri, Oct 09, 2020 at 12:42:54PM -0700, ira.weiny@...el.com wrote:
> > +static inline void pks_update_protection(int pkey, unsigned long protection)
> > +{
> > +	current->thread.saved_pkrs = update_pkey_val(current->thread.saved_pkrs,
> > +						     pkey, protection);
> > +	preempt_disable();
> > +	write_pkrs(current->thread.saved_pkrs);
> > +	preempt_enable();
> > +}
> 
> write_pkrs() already disables preemption itself. Wrapping it in yet
> another layer is useless.

I was thinking the update to saved_pkrs needed this protection as well and that
was to be included in the preemption disable.  But that too is incorrect.

I've removed this preemption disable.

Thanks,
Ira