On Mon, Sep 05, 2022 at 06:35:17PM +0300, Kirill A. Shutemov wrote:
> What about something like this?
>
> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
> index 803241dfc473..868d2730884b 100644
> --- a/arch/x86/include/asm/uaccess.h
> +++ b/arch/x86/include/asm/uaccess.h
> @@ -30,8 +30,10 @@ static inline bool pagefault_disabled(void);
> */
> #define untagged_addr(mm, addr) ({ \
> u64 __addr = (__force u64)(addr); \
> - s64 sign = (s64)__addr >> 63; \
> - __addr &= (mm)->context.untag_mask | sign; \
> + if (static_cpu_has(X86_FEATURE_LAM)) { \
> + s64 sign = (s64)__addr >> 63; \
> + __addr &= (mm)->context.untag_mask | sign; \
> + } \
> (__force __typeof__(addr))__addr; \
> })
Well, if you go throught the trouble of adding it, might as well use a
regular static branch and only enable it once there's an actual user,
no?
