linux-kernel - Re: [PATCH v3 10/11] x86/mm: Enable CR4.PCIDE on supported systems

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Date:   Wed, 21 Jun 2017 15:40:01 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andy Lutomirski <luto@...nel.org>
cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...en8.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Nadav Amit <nadav.amit@...il.com>,
        Rik van Riel <riel@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [PATCH v3 10/11] x86/mm: Enable CR4.PCIDE on supported systems

On Wed, 21 Jun 2017, Thomas Gleixner wrote:

> On Tue, 20 Jun 2017, Andy Lutomirski wrote:
> > +	/* Set up PCID */
> > +	if (cpu_has(c, X86_FEATURE_PCID)) {
> > +		if (cpu_has(c, X86_FEATURE_PGE)) {
> > +			cr4_set_bits(X86_CR4_PCIDE);
> 
> So I assume that you made sure that the PCID bits in CR3 are zero under all
> circumstances as setting PCIDE would cause a #GP if not.

And what happens on kexec etc? We need to reset the asid and PCIDE I assume.

Thanks,

	tglx