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SubjectRe: [PATCH 04/23] x86, tlb: make CR4-based TLB flushes more robust

On Wed, 1 Nov 2017, Dave Hansen wrote:

> On 11/01/2017 02:25 PM, Thomas Gleixner wrote:
> >> cr4 = this_cpu_read(cpu_tlbstate.cr4);
> >> - /* clear PGE */
> >> - native_write_cr4(cr4 & ~X86_CR4_PGE);
> >> - /* write old PGE again and flush TLBs */
> >> + /*
> >> + * This function is only called on systems that support X86_CR4_PGE
> >> + * and where always set X86_CR4_PGE. Warn if we are called without
> >> + * PGE set.
> >> + */
> >> + WARN_ON_ONCE(!(cr4 & X86_CR4_PGE));
> > Because if CR4_PGE is not set, this warning triggers. So this defeats the
> > toggle mode you are implementing.
>
> The warning is there because there is probably plenty of *other* stuff
> that breaks if we have X86_FEATURE_PGE=1, but CR4.PGE=0.
>
> The point of this was to make this function do the right thing no matter
> what, but warn if it gets called in an unexpected way.

Fair enough. Can you please reflect that in the changelog ?

Thanks,

tglx

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