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authorFenghua Yu <fenghua.yu@intel.com>2011-05-17 15:29:12 -0700
committerH. Peter Anvin <hpa@linux.intel.com>2011-05-17 15:40:25 -0700
commit509731336313b3799cf03071d72c64fa6383895e (patch)
treec3591cee18b04a1506e048aa51698c7af7aa9fc2 /arch
parent161ec53c702ce9df2f439804dfb9331807066daa (diff)
x86, alternative, doc: Add comment for applying alternatives order
Some string operation functions may be patched twice, e.g. on enhanced REP MOVSB /STOSB processors, memcpy is patched first by fast string alternative function, then it is patched by enhanced REP MOVSB/STOSB alternative function. Add comment for applying alternatives order to warn people who may change the applying alternatives order for any reason. [ Documentation-only patch ] Signed-off-by: Fenghua Yu <fenghua.yu@intel.com> Link: http://lkml.kernel.org/r/1305671358-14478-4-git-send-email-fenghua.yu@intel.com Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kernel/alternative.c9
1 files changed, 9 insertions, 0 deletions
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 4a234677e213..f4fe15ddcf94 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -210,6 +210,15 @@ void __init_or_module apply_alternatives(struct alt_instr *start,
u8 insnbuf[MAX_PATCH_LEN];
DPRINTK("%s: alt table %p -> %p\n", __func__, start, end);
+ /*
+ * The scan order should be from start to end. A later scanned
+ * alternative code can overwrite a previous scanned alternative code.
+ * Some kernel functions (e.g. memcpy, memset, etc) use this order to
+ * patch code.
+ *
+ * So be careful if you want to change the scan order to any other
+ * order.
+ */
for (a = start; a < end; a++) {
u8 *instr = a->instr;
BUG_ON(a->replacementlen > a->instrlen);