linux-kernel - [tip:x86/asm] x86/io: Unroll string I/O when SEV is active

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Date:   Tue, 7 Nov 2017 06:47:53 -0800
From:   tip-bot for Tom Lendacky <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     bp@...en8.de, thomas.lendacky@....com, mingo@...nel.org,
        bp@...e.de, tglx@...utronix.de, hpa@...or.com,
        linux-kernel@...r.kernel.org, andriy.shevchenko@...ux.intel.com,
        brijesh.singh@....com, David.Laight@...LAB.COM, arnd@...db.de
Subject: [tip:x86/asm] x86/io: Unroll string I/O when SEV is active

Commit-ID:  606b21d4a6498c23632a4693c81b7b24feedd038
Gitweb:     https://git.kernel.org/tip/606b21d4a6498c23632a4693c81b7b24feedd038
Author:     Tom Lendacky <thomas.lendacky@....com>
AuthorDate: Fri, 20 Oct 2017 09:30:55 -0500
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Tue, 7 Nov 2017 15:35:59 +0100

x86/io: Unroll string I/O when SEV is active

Secure Encrypted Virtualization (SEV) does not support string I/O, so
unroll the string I/O operation into a loop operating on one element at
a time.

[ tglx: Gave the static key a real name instead of the obscure __sev ]

Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
Signed-off-by: Brijesh Singh <brijesh.singh@....com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Borislav Petkov <bp@...e.de>
Tested-by: Borislav Petkov <bp@...e.de>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: kvm@...r.kernel.org
Cc: David Laight <David.Laight@...LAB.COM>
Cc: Borislav Petkov <bp@...en8.de>
Link: https://lkml.kernel.org/r/20171020143059.3291-14-brijesh.singh@amd.com

---
 arch/x86/include/asm/io.h | 43 +++++++++++++++++++++++++++++++++++++++----
 arch/x86/mm/mem_encrypt.c |  8 ++++++++
 2 files changed, 47 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index 11398d5..93ae8ae 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -266,6 +266,21 @@ static inline void slow_down_io(void)
 
 #endif
 
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+#include <linux/jump_label.h>
+
+extern struct static_key_false sev_enable_key;
+static inline bool sev_key_active(void)
+{
+	return static_branch_unlikely(&sev_enable_key);
+}
+
+#else /* !CONFIG_AMD_MEM_ENCRYPT */
+
+static inline bool sev_key_active(void) { return false; }
+
+#endif /* CONFIG_AMD_MEM_ENCRYPT */
+
 #define BUILDIO(bwl, bw, type)						\
 static inline void out##bwl(unsigned type value, int port)		\
 {									\
@@ -296,14 +311,34 @@ static inline unsigned type in##bwl##_p(int port)			\
 									\
 static inline void outs##bwl(int port, const void *addr, unsigned long count) \
 {									\
-	asm volatile("rep; outs" #bwl					\
-		     : "+S"(addr), "+c"(count) : "d"(port) : "memory");	\
+	if (sev_key_active()) {						\
+		unsigned type *value = (unsigned type *)addr;		\
+		while (count) {						\
+			out##bwl(*value, port);				\
+			value++;					\
+			count--;					\
+		}							\
+	} else {							\
+		asm volatile("rep; outs" #bwl				\
+			     : "+S"(addr), "+c"(count)			\
+			     : "d"(port) : "memory");			\
+	}								\
 }									\
 									\
 static inline void ins##bwl(int port, void *addr, unsigned long count)	\
 {									\
-	asm volatile("rep; ins" #bwl					\
-		     : "+D"(addr), "+c"(count) : "d"(port) : "memory");	\
+	if (sev_key_active()) {						\
+		unsigned type *value = (unsigned type *)addr;		\
+		while (count) {						\
+			*value = in##bwl(port);				\
+			value++;					\
+			count--;					\
+		}							\
+	} else {							\
+		asm volatile("rep; ins" #bwl				\
+			     : "+D"(addr), "+c"(count)			\
+			     : "d"(port) : "memory");			\
+	}								\
 }
 
 BUILDIO(b, b, char)
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index fd9c7bb..d29b783 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -41,6 +41,8 @@ static char sme_cmdline_off[] __initdata = "off";
  */
 u64 sme_me_mask __section(.data) = 0;
 EXPORT_SYMBOL_GPL(sme_me_mask);
+DEFINE_STATIC_KEY_FALSE(sev_enable_key);
+EXPORT_SYMBOL_GPL(sev_enable_key);
 
 static bool sev_enabled __section(.data);
 
@@ -313,6 +315,12 @@ void __init mem_encrypt_init(void)
 	if (sev_active())
 		dma_ops = &sev_dma_ops;
 
+	/*
+	 * With SEV, we need to unroll the rep string I/O instructions.
+	 */
+	if (sev_active())
+		static_branch_enable(&sev_enable_key);
+
 	pr_info("AMD %s active\n",
 		sev_active() ? "Secure Encrypted Virtualization (SEV)"
 			     : "Secure Memory Encryption (SME)");