On Wed, Oct 09, 2024 at 09:34:37AM +0200, Peter Zijlstra wrote:
> You need ifdeffery either way around, either directly like this or for
> that macro. This is simple and straight forward.
Nothing in this file full of macros is simple. In any case, I would've done
this as the ifdeffery is shorter and the macro is simpler. We have this coding
pattern in a lot of headers, abstracting 32-bit vs 64-bit machine details, and
it is a very common and familiar one:
/*
* In 32bit mode, the memory operand must be a %cs reference. The data
* segments may not be usable (vm86 mode), and the stack segment may not be
* flat (ESPFIX32).
*/
#ifdef CONFIG_X86_64
#define VERW_ARG "verw mds_verw_sel(%rip)"
#else /* CONFIG_X86_32 */
#define VERW_ARG "verw %cs:mds_verw_sel"
#endif
/*
* Macro to execute VERW instruction that mitigate transient data sampling
* attacks such as MDS. On affected systems a microcode update overloaded VERW
* instruction to also clear the CPU buffers. VERW clobbers CFLAGS.ZF.
*
* Note: Only the memory operand variant of VERW clears the CPU buffers.
*/
.macro CLEAR_CPU_BUFFERS
ALTERNATIVE "", VERW_ARG, X86_FEATURE_CLEAR_CPU_BUF
.endm
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
