linux-kernel - Re: [NEEDS-REVIEW] [PATCH V3 04/10] x86/pks: Preserve the PKRS MSR on context switch

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Message-ID: <20201218041012.GC2506510@iweiny-DESK2.sc.intel.com>
Date:   Thu, 17 Dec 2020 20:10:12 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-doc@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>,
        Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [NEEDS-REVIEW] [PATCH V3 04/10] x86/pks: Preserve the PKRS MSR
 on context switch

On Thu, Dec 17, 2020 at 12:41:50PM -0800, Dave Hansen wrote:
> On 11/6/20 3:29 PM, ira.weiny@...el.com wrote:
> >  void disable_TSC(void)
> > @@ -644,6 +668,8 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p)
> >  
> >  	if ((tifp ^ tifn) & _TIF_SLD)
> >  		switch_to_sld(tifn);
> > +
> > +	pks_sched_in();
> >  }
> 
> Does the selftest for this ever actually schedule()?

At this point I'm not sure.  This code has been in since the beginning.  So its
seen a lot of soak time.

> 
> I see it talking about context switching, but I don't immediately see
> how it would.

We were trying to force parent and child to run on the same CPU.  I suspect
something is wrong in the timing of that test.

Ira