x86/bugs: Reverse instruction order of CLEAR_CPU_BUFFERS

JIRA: https://issues.redhat.com/browse/RHEL-31226
Upstream Status: RHEL only

In the CLEAR_CPU_BUFFERS macro, the use of a VERW instruction with %rip
relative addressing in the newinstr portion of ALTERNATIVE depends on the
presence of commit 270a69c ("x86/alternative: Support relocations
in alternatives") and related ones. Break that dependency by reversing
the ordering of the two instructions and use ALT_NOT() for the feature
flag so that the correct %rip offset will be present without any special
handling.

This will also allow the RDFS fix to be backported to older RHEL releases
without requiring an additional set of x86/alternative commits.

Signed-off-by: Waiman Long <longman@redhat.com>

Author: Waiman-Long

arch/x86/include/asm/nospec-branch.h

@@ -323,7 +323,7 @@
  * Note: Only the memory operand variant of VERW clears the CPU buffers.
  */
 .macro CLEAR_CPU_BUFFERS
-	ALTERNATIVE "", __stringify(verw _ASM_RIP(mds_verw_sel)), X86_FEATURE_CLEAR_CPU_BUF
+	ALTERNATIVE __stringify(verw _ASM_RIP(mds_verw_sel)), "", ALT_NOT(X86_FEATURE_CLEAR_CPU_BUF)
 .endm
 
 #else /* __ASSEMBLY__ */