linux-kernel - [RFC PATCH v1 16/18] x86: Do not specify encrypted memory for VGA mapping

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Date:	Tue, 26 Apr 2016 17:58:45 -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 16/18] x86: Do not specify encrypted memory for VGA
 mapping

Since the VGA memory needs to be accessed unencrypted be sure that the
memory encryption mask is not set for the VGA range being mapped.

Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
---
 arch/x86/include/asm/vga.h |   13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/x86/include/asm/vga.h b/arch/x86/include/asm/vga.h
index c4b9dc2..55fe164 100644
--- a/arch/x86/include/asm/vga.h
+++ b/arch/x86/include/asm/vga.h
@@ -7,12 +7,25 @@
 #ifndef _ASM_X86_VGA_H
 #define _ASM_X86_VGA_H
 
+#include <asm/mem_encrypt.h>
+
 /*
  *	On the PC, we can just recalculate addresses and then
  *	access the videoram directly without any black magic.
+ *	To support memory encryption however, we need to access
+ *	the videoram as un-encrypted memory.
  */
 
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+#define VGA_MAP_MEM(x, s)					\
+({								\
+	unsigned long start = (unsigned long)phys_to_virt(x);	\
+	sme_set_mem_dec((void *)start, s);			\
+	start;							\
+})
+#else
 #define VGA_MAP_MEM(x, s) (unsigned long)phys_to_virt(x)
+#endif
 
 #define vga_readb(x) (*(x))
 #define vga_writeb(x, y) (*(y) = (x))