Date: Wed, 21 Jun 2017 15:40:01 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Andy Lutomirski <luto@kernel.org>
cc: x86@kernel.org, linux-kernel@vger.kernel.org,
        Borislav Petkov <bp@alien8.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Nadav Amit <nadav.amit@gmail.com>, Rik van Riel <riel@redhat.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>, Juergen Gross <jgross@suse.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [PATCH v3 10/11] x86/mm: Enable CR4.PCIDE on supported systems
In-Reply-To: <alpine.DEB.2.20.1706211127460.2328@nanos>
Message-ID: <alpine.DEB.2.20.1706211539080.2328@nanos>
References: <cover.1498022414.git.luto@kernel.org> <57c1d18b1c11f9bc9a3bcf8bdee38033415e1a13.1498022414.git.luto@kernel.org> <alpine.DEB.2.20.1706211127460.2328@nanos>
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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