[PATCH v5 05/12] x86/alternative: support ALTERNATIVE_TERNARY

Juergen Gross
2021-03-08T12:29:57Z

Add ALTERNATIVE_TERNARY support for replacing an initial instruction
with either of two instructions depending on a feature:

ALTERNATIVE_TERNARY "default_instr", FEATURE_NR,
"feature_on_instr", "feature_off_instr"

which will start with "default_instr" and at patch time will, depending
on FEATURE_NR being set or not, patch that with either
"feature_on_instr" or "feature_off_instr".

Signed-off-by: Juergen Gross <jgross@suse.com>
---
V3:
- new patch
V4:
- use X86_FEATURE_ALWAYS instead of negated feature (Boris Petkov)
- unfortunately this isn't enough to get rid of the "not feature"
support, as this is needed in the patch "x86/paravirt: switch
functions with custom code to ALTERNATIVE", too
V5:
- carve out the "not feature" part
---
arch/x86/include/asm/alternative-asm.h | 4 ++++
arch/x86/include/asm/alternative.h | 6 ++++++
2 files changed, 10 insertions(+)

diff --git a/arch/x86/include/asm/alternative-asm.h b/arch/x86/include/asm/alternative-asm.h
index 9a1763550217..ba0aad81d3bb 100644
--- a/arch/x86/include/asm/alternative-asm.h
+++ b/arch/x86/include/asm/alternative-asm.h
@@ -115,6 +115,10 @@
.popsection
.endm

+#define ALTERNATIVE_TERNARY(oldinstr, feature, newinstr1, newinstr2) \
+ ALTERNATIVE_2 oldinstr, newinstr2, X86_FEATURE_ALWAYS, \
+ newinstr1, feature
+
#endif /* __ASSEMBLY__ */

#endif /* _ASM_X86_ALTERNATIVE_ASM_H */
diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index b9749cf21ada..693991f8fe89 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -183,6 +183,9 @@ static inline int alternatives_text_reserved(void *start, void *end)
ALTINSTR_REPLACEMENT(newinstr2, 2) \
".popsection\n"

+#define ALTERNATIVE_TERNARY(oldinstr, feature, newinstr1, newinstr2) \
+ ALTERNATIVE_2(oldinstr, newinstr2, X86_FEATURE_ALWAYS, newinstr1, feature)
+
#define ALTERNATIVE_3(oldinsn, newinsn1, feat1, newinsn2, feat2, newinsn3, feat3) \
OLDINSTR_3(oldinsn, 1, 2, 3) \
".pushsection .altinstructions,\"a\"\n" \
@@ -214,6 +217,9 @@ static inline int alternatives_text_reserved(void *start, void *end)
#define alternative_2(oldinstr, newinstr1, feature1, newinstr2, feature2) \
asm_inline volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2) ::: "memory")

+#define alternative_ternary(oldinstr, feature, newinstr1, newinstr2) \
+ asm_inline volatile(ALTERNATIVE_TERNARY(oldinstr, feature, newinstr1, newinstr2) ::: "memory")
+
/*
* Alternative inline assembly with input.
*
--
2.26.2