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Re: [patch 3/3] x86/process: Optimize TIF_NOTSC switch

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On Thu, 15 Dec 2016, Andy Lutomirski wrote:
> On Thu, Dec 15, 2016 at 8:44 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> > +static inline void cr4_toggle_bits(unsigned long mask)
> > +{
> > +       unsigned long cr4;
> > +
> > +       cr4 = this_cpu_read(cpu_tlbstate.cr4);
> > +       cr4 ^= mask;
> > +       this_cpu_write(cpu_tlbstate.cr4, cr4);
> > +       __write_cr4(cr4);
> > +}
> 
> This scares me for the same reason as BTF, although this should at
> least be less fragile.  But how about:

If that is fragile then all cr4 manipulation code is fragile because it
relies on cpu_tlbstate.cr4. The TIF flag and that per cpu thing are kept in
sync.

Thanks,

	tglx

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[patch 3/3] x86/process: Optimize TIF_NOTSC switch Thomas Gleixner <tglx@linutronix.de> - 2016-12-15 17:50 +0100
  Re: [patch 3/3] x86/process: Optimize TIF_NOTSC switch Andy Lutomirski <luto@amacapital.net> - 2016-12-15 18:40 +0100
    Re: [patch 3/3] x86/process: Optimize TIF_NOTSC switch Thomas Gleixner <tglx@linutronix.de> - 2016-12-16 10:00 +0100
      Re: [patch 3/3] x86/process: Optimize TIF_NOTSC switch Andy Lutomirski <luto@amacapital.net> - 2016-12-16 19:40 +0100

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