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Subject[PATCH v0 07/12] x86, microcode, AMD: Check before applying a patch
Date
From: Borislav Petkov <borislav.petkov@amd.com>

Make sure we're actually applying a microcode patch to a core which
really needs it.

This brings only a very very very minor slowdown on F10:

0.032218828 sec vs 0.056010626 sec with this patch.

And small speedup on F15:

0.487089449 sec vs 0.180551162 sec (from perf output).

Also, fixup comments while at it.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
---
arch/x86/kernel/microcode_amd.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/microcode_amd.c b/arch/x86/kernel/microcode_amd.c
index 94213387a3d1..8fdf7d99b804 100644
--- a/arch/x86/kernel/microcode_amd.c
+++ b/arch/x86/kernel/microcode_amd.c
@@ -202,11 +202,18 @@ static int apply_microcode_amd(int cpu)
if (mc_amd == NULL)
return 0;

- wrmsrl(MSR_AMD64_PATCH_LOADER, (u64)(long)&mc_amd->hdr.data_code);
- /* get patch id after patching */
rdmsr(MSR_AMD64_PATCH_LEVEL, rev, dummy);

- /* check current patch id and patch's id for match */
+ /* need to apply patch? */
+ if (rev >= mc_amd->hdr.patch_id) {
+ c->microcode = rev;
+ return 0;
+ }
+
+ wrmsrl(MSR_AMD64_PATCH_LOADER, (u64)(long)&mc_amd->hdr.data_code);
+
+ /* verify patch application was successful */
+ rdmsr(MSR_AMD64_PATCH_LEVEL, rev, dummy);
if (rev != mc_amd->hdr.patch_id) {
pr_err("CPU%d: update failed for patch_level=0x%08x\n",
cpu, mc_amd->hdr.patch_id);
--
1.7.11.rc1


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