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Tue, 29 Oct 2024 21:46:34 +0000 Message-ID: Date: Tue, 29 Oct 2024 14:46:30 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 01/16] x86/cpu: Enumerate the LASS feature bits To: "Kirill A. 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For example, text_poke_mem* doesn't get flagged by SMAP but only by LASS. I guess the answer is related to paging but it would be useful to describe it in a commit message or a comment. I am imagining a scenario where someone needs to use one of these stac()/clac() pairs but isn't sure which one to use. Both of them would seem to work but one is better suited than other. >> + * LASS (X86_FEATURE_LASS) enforcement, which helps readability and >> + * avoids AC flag flipping on CPUs that don't support LASS. >> + */ > > Maybe add a new line here? The comment is for the group of helpers, not > for clac() specifically. > Also, it might be better to move the common text "/* Note: a barrier is implicit in alternative() */" to the above comment as well. Repeating it 4 times makes it unnecessarily distracting to read the code. >> static __always_inline void clac(void) >> { >> /* Note: a barrier is implicit in alternative() */ >> @@ -39,6 +45,18 @@ static __always_inline void stac(void) >> alternative("", __ASM_STAC, X86_FEATURE_SMAP); >> } >> >> +static __always_inline void lass_clac(void) >> +{ >> + /* Note: a barrier is implicit in alternative() */ >> + alternative("", __ASM_CLAC, X86_FEATURE_LASS); >> +} >> + >> +static __always_inline void lass_stac(void) >> +{ >> + /* Note: a barrier is implicit in alternative() */ >> + alternative("", __ASM_STAC, X86_FEATURE_LASS); >> +} >> +