[xen master] x86/alternatives: allow replacement code snippets to be re-used

[patchbot@xxxxxxx]

commit b458596ac3b2ac3c365769d4fd278ae17aa76d22
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri May 2 09:44:49 2025 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri May 2 09:44:49 2025 +0200

    x86/alternatives: allow replacement code snippets to be re-used
    
    In a number of cases we use ALTERNATIVE_2 with both replacement insns /
    insn sequences being identical. Avoid emitting the same code twice, and
    instead alias the necessary helper labels to the existing ones.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/include/asm/alternative-asm.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/xen/arch/x86/include/asm/alternative-asm.h 
b/xen/arch/x86/include/asm/alternative-asm.h
index 83e8594f0e..22da9f89f1 100644
--- a/xen/arch/x86/include/asm/alternative-asm.h
+++ b/xen/arch/x86/include/asm/alternative-asm.h
@@ -51,6 +51,8 @@
 
 #define decl_repl(insn, nr)     .L\@_repl_s\()nr: insn; .L\@_repl_e\()nr:
 #define repl_len(nr)           (.L\@_repl_e\()nr  -     .L\@_repl_s\()nr)
+#define clone_repl(new, old)    .equiv .L\@_repl_s\()new, .L\@_repl_s\()old; \
+                                .equiv .L\@_repl_e\()new, .L\@_repl_e\()old
 
 #define as_max(a, b)           ((a) ^ (((a) ^ (b)) & -as_true((a) < (b))))
 
@@ -100,7 +102,11 @@
     .section .altinstr_replacement, "ax", @progbits
 
     decl_repl(\newinstr1, 1)
+    .ifnes "\newinstr2", "\newinstr1"
     decl_repl(\newinstr2, 2)
+    .else
+    clone_repl(2, 1)
+    .endif
 
     .popsection
 .endm
--
generated by git-patchbot for /home/xen/git/xen.git#master