Patch "x86/mce: Annotate mce_rd/wrmsrl() with noinstr" has been added to the 5.8-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    x86/mce: Annotate mce_rd/wrmsrl() with noinstr

to the 5.8-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-mce-annotate-mce_rd-wrmsrl-with-noinstr.patch
and it can be found in the queue-5.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit da43b0f9542f40da1920398599a9c7f3309e419e
Author: Borislav Petkov <bp@xxxxxxx>
Date:   Mon Sep 14 19:21:28 2020 +0200

    x86/mce: Annotate mce_rd/wrmsrl() with noinstr
    
    [ Upstream commit e100777016fdf6ec3a9d7c1773b15a2b5eca6c55 ]
    
    They do get called from the #MC handler which is already marked
    "noinstr".
    
    Commit
    
      e2def7d49d08 ("x86/mce: Make mce_rdmsrl() panic on an inaccessible MSR")
    
    already got rid of the instrumentation in the MSR accessors, fix the
    annotation now too, in order to get rid of:
    
      vmlinux.o: warning: objtool: do_machine_check()+0x4a: call to mce_rdmsrl() leaves .noinstr.text section
    
    Signed-off-by: Borislav Petkov <bp@xxxxxxx>
    Link: https://lkml.kernel.org/r/20200915194020.28807-1-bp@xxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 14e4b4d17ee5b..d8dca24feccbe 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -371,16 +371,25 @@ static int msr_to_offset(u32 msr)
 }
 
 /* MSR access wrappers used for error injection */
-static u64 mce_rdmsrl(u32 msr)
+static noinstr u64 mce_rdmsrl(u32 msr)
 {
 	u64 v;
 
 	if (__this_cpu_read(injectm.finished)) {
-		int offset = msr_to_offset(msr);
+		int offset;
+		u64 ret;
 
+		instrumentation_begin();
+
+		offset = msr_to_offset(msr);
 		if (offset < 0)
-			return 0;
-		return *(u64 *)((char *)this_cpu_ptr(&injectm) + offset);
+			ret = 0;
+		else
+			ret = *(u64 *)((char *)this_cpu_ptr(&injectm) + offset);
+
+		instrumentation_end();
+
+		return ret;
 	}
 
 	if (rdmsrl_safe(msr, &v)) {
@@ -396,13 +405,19 @@ static u64 mce_rdmsrl(u32 msr)
 	return v;
 }
 
-static void mce_wrmsrl(u32 msr, u64 v)
+static noinstr void mce_wrmsrl(u32 msr, u64 v)
 {
 	if (__this_cpu_read(injectm.finished)) {
-		int offset = msr_to_offset(msr);
+		int offset;
 
+		instrumentation_begin();
+
+		offset = msr_to_offset(msr);
 		if (offset >= 0)
 			*(u64 *)((char *)this_cpu_ptr(&injectm) + offset) = v;
+
+		instrumentation_end();
+
 		return;
 	}
 	wrmsrl(msr, v);