linux-kernel - [RFC PATCH v1 01/18] x86: Set the write-protect cache mode for AMD processors

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Message-ID: <20160426224520.13079.67248.stgit@tlendack-t1.amdoffice.net>
Date:	Tue, 26 Apr 2016 17:45:20 -0500
From:	Tom Lendacky <thomas.lendacky@....com>
To:	<linux-arch@...r.kernel.org>, <linux-efi@...r.kernel.org>,
	<kvm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
	<x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<kasan-dev@...glegroups.com>, <linux-mm@...ck.org>,
	<iommu@...ts.linux-foundation.org>
CC:	Radim Krčmář <rkrcmar@...hat.com>,
	Arnd Bergmann <arnd@...db.de>,
	Jonathan Corbet <corbet@....net>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Joerg Roedel <joro@...tes.org>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	"Ingo Molnar" <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	"Alexander Potapenko" <glider@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Dmitry Vyukov" <dvyukov@...gle.com>
Subject: [RFC PATCH v1 01/18] x86: Set the write-protect cache mode for AMD
 processors

For AMD processors that support PAT, set the write-protect cache mode
(_PAGE_CACHE_MODE_WP) entry to the actual write-protect value (x05).

Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
---
 arch/x86/mm/pat.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index fb0604f..dda78ed 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -345,6 +345,8 @@ void pat_init(void)
 		 * we lose performance without causing a correctness issue.
 		 * Pentium 4 erratum N46 is an example for such an erratum,
 		 * although we try not to use PAT at all on affected CPUs.
+		 * AMD processors support write-protect so initialize the
+		 * PAT slot 5 appropriately.
 		 *
 		 *  PTE encoding:
 		 *      PAT
@@ -356,7 +358,7 @@ void pat_init(void)
 		 *      010    2    UC-: _PAGE_CACHE_MODE_UC_MINUS
 		 *      011    3    UC : _PAGE_CACHE_MODE_UC
 		 *      100    4    WB : Reserved
-		 *      101    5    WC : Reserved
+		 *      101    5    WC : Reserved (AMD: _PAGE_CACHE_MODE_WP)
 		 *      110    6    UC-: Reserved
 		 *      111    7    WT : _PAGE_CACHE_MODE_WT
 		 *
@@ -364,7 +366,12 @@ void pat_init(void)
 		 * corresponding types in the presence of PAT errata.
 		 */
 		pat = PAT(0, WB) | PAT(1, WC) | PAT(2, UC_MINUS) | PAT(3, UC) |
-		      PAT(4, WB) | PAT(5, WC) | PAT(6, UC_MINUS) | PAT(7, WT);
+		      PAT(4, WB) | PAT(6, UC_MINUS) | PAT(7, WT);
+
+		if (c->x86_vendor == X86_VENDOR_AMD)
+			pat |= PAT(5, WP);
+		else
+			pat |= PAT(5, WC);
 	}
 
 	if (!boot_cpu_done) {