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x86/retpoline: Add X86_FEATURE_RETPOLINE_COMMON and split RETPLINE/RETPOLINE_AMD

PATCH New Andi Kleen 1 participant 2 messages Jan 10, 2018

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Andi Kleen

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PATCH v2 1/2 x86/retpoline: Add X86_FEATURE_RETPOLINE_COMMON and split RETPLINE/RETPOLINE_AMD

From: Andi Kleen <[email protected]>

On 64bit we want to split X86_FEATURE_RETPOLINE and X86_FEATURE_RETPOLINE_AMD, so that only one is set. This enables new simpler ALTERNATIVE sequences.

But 32bit requires a common flag because it uses common code for both.

So add a new X86_FEATURE_RETPOLINE_COMMON that is always set when either X86_FEATURE_RETPOLINE or X86_FEATURE_RETPOLINE_AMD are set.

And then unset X86_FEATURE_RETPOLINE for AMD.

Signed-off-by Andi Kleen <[email protected]>
---
 arch/x86/include/asm/cpufeatures.h | 1 +
 arch/x86/kernel/cpu/bugs.c         | 5 ++++-
 2 files changed, 5 insertions(+), 1 deletion(-)
arch/x86/include/asm/cpufeatures.h +1 -0
index f275447862f4..54ec16ef08d8 100644
@@ -211,6 +211,7 @@
 #define X86_FEATURE_AVX512_4FMAPS	( 7*32+17) /* AVX-512 Multiply Accumulation Single precision */
 
 #define X86_FEATURE_MBA			( 7*32+18) /* Memory Bandwidth Allocation */
+#define X86_FEATURE_RETPOLINE_COMMON	( 7*32+19) /* Common code for both RETPOLINE and RETPOLINE_AMD */
 
 /* Virtualization flags: Linux defined, word 8 */
 #define X86_FEATURE_TPR_SHADOW		( 8*32+ 0) /* Intel TPR Shadow */
arch/x86/kernel/cpu/bugs.c +4 -1
index b957f771a5b7..241eae66a86b 100644
@@ -155,8 +155,10 @@ void __init spectre_v2_check_boottime_disable(void)
 	retpoline_generic:
 		spectre_v2_enabled = retp_compiler() ?
 			SPECTRE_V2_RETPOLINE_GENERIC : SPECTRE_V2_RETPOLINE_MINIMAL;
+		setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
 	}
-	setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
+	setup_force_cpu_cap(X86_FEATURE_RETPOLINE_COMMON);
+
 	return;
 #else
 retpoline:

@@ -167,6 +169,7 @@ void __init spectre_v2_check_boottime_disable(void)
 disable:
 	setup_clear_cpu_cap(X86_FEATURE_RETPOLINE);
 	setup_clear_cpu_cap(X86_FEATURE_RETPOLINE_AMD);
+	setup_clear_cpu_cap(X86_FEATURE_RETPOLINE_COMMON);
 	return;
 }
Signature · 1 line
2.14.3
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#1 lore raw

PATCH v2 2/2 x86/retpoline: Use X86_RETPOLINE_COMMON to enable 32bit retpoline

From: Andi Kleen <[email protected]>

32bit uses a single retpoline sequence for AMD/Intel. Previously X86_RETPOLINE was always set for AMD/Intel but that's not true anymore. So now use the new X86_FEATURE_RETPOLINE_COMMON flag that is set for both.

Signed-off-by Andi Kleen <[email protected]>
---
 arch/x86/include/asm/nospec-branch.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
arch/x86/include/asm/nospec-branch.h +2 -2
index c1cef78f0e12..bbd5343f2fea 100644
@@ -116,7 +116,7 @@
 # define CALL_NOSPEC ALTERNATIVE(				\
 	"call *%[thunk_target]\n",				\
 	"call __x86_indirect_thunk_%V[thunk_target]\n",		\
-	X86_FEATURE_RETPOLINE)
+	X86_FEATURE_RETPOLINE_COMMON)
 # define THUNK_TARGET(addr) [thunk_target] "r" (addr)
 #elif defined(CONFIG_X86_32) && defined(CONFIG_RETPOLINE)
 /*

@@ -142,7 +142,7 @@
 	"       .align 16\n"					\
 	"do_call%=:\n"						\
 	"	call   do_retpoline%=;\n",			\
-	X86_FEATURE_RETPOLINE)
+	X86_FEATURE_RETPOLINE_COMMON)
 
 # define THUNK_TARGET(addr) [thunk_target] "rm" (addr)
 #else /* No retpoline */
Signature · 1 line
2.14.3