linux-kernel - Re: [PATCH 10/14] x86/alternative: Convert ALTERNATIVE

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Date: Fri, 31 May 2024 13:00:55 -0400
From: Brian Gerst <brgerst@...il.com>
To: Borislav Petkov <bp@...nel.org>
Cc: X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>, 
	"Borislav Petkov (AMD)" <bp@...en8.de>
Subject: Re: [PATCH 10/14] x86/alternative: Convert ALTERNATIVE_3()

On Fri, May 31, 2024 at 8:41 AM Borislav Petkov <bp@...nel.org> wrote:
>
> From: "Borislav Petkov (AMD)" <bp@...en8.de>
>
> Fixup label numbering too as the new macros have new label numbers.
>
> Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
> ---
>  arch/x86/include/asm/alternative.h | 24 ++++--------------------
>  arch/x86/kernel/fpu/xstate.h       |  4 ++--
>  2 files changed, 6 insertions(+), 22 deletions(-)
>
> diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
> index 73ee18705ef1..0df99855e003 100644
> --- a/arch/x86/include/asm/alternative.h
> +++ b/arch/x86/include/asm/alternative.h
> @@ -277,26 +277,10 @@ static inline int alternatives_text_reserved(void *start, void *end)
>         N_ALTERNATIVE_2(oldinstr, newinstr_no, X86_FEATURE_ALWAYS,      \
>                       newinstr_yes, ft_flags)
>
> -#define ALTERNATIVE_3(oldinsn, newinsn1, ft_flags1, newinsn2, ft_flags2, \
> -                       newinsn3, ft_flags3)                            \
> -       OLDINSTR_3(oldinsn, 1, 2, 3)                                    \
> -       ".pushsection .altinstructions,\"a\"\n"                         \
> -       ALTINSTR_ENTRY(ft_flags1, 1)                                    \
> -       ALTINSTR_ENTRY(ft_flags2, 2)                                    \
> -       ALTINSTR_ENTRY(ft_flags3, 3)                                    \
> -       ".popsection\n"                                                 \
> -       ".pushsection .altinstr_replacement, \"ax\"\n"                  \
> -       ALTINSTR_REPLACEMENT(newinsn1, 1)                               \
> -       ALTINSTR_REPLACEMENT(newinsn2, 2)                               \
> -       ALTINSTR_REPLACEMENT(newinsn3, 3)                               \
> -       ".popsection\n"
> -
> -
> -#define N_ALTERNATIVE_3(oldinst, newinst1, flag1, newinst2, flag2,     \
> -                     newinst3, flag3)                                  \
> -       N_ALTERNATIVE(N_ALTERNATIVE_2(oldinst, newinst1, flag1, newinst2, flag2), \
> -                     newinst3, flag3)
> -
> +#define ALTERNATIVE_3(oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2, \
> +                       newinstr3, ft_flags3)                           \
> +       N_ALTERNATIVE(N_ALTERNATIVE_2(oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2), \
> +                     newinstr3, ft_flags3)
>  /*
>   * Alternative instructions for different CPU types or capabilities.
>   *
> diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
> index 05df04f39628..4fe8501efc6c 100644
> --- a/arch/x86/kernel/fpu/xstate.h
> +++ b/arch/x86/kernel/fpu/xstate.h
> @@ -108,7 +108,7 @@ static inline u64 xfeatures_mask_independent(void)
>   *
>   * We use XSAVE as a fallback.
>   *
> - * The 661 label is defined in the ALTERNATIVE* macros as the address of the
> + * The 771 label is defined in the ALTERNATIVE* macros as the address of the
>   * original instruction which gets replaced. We need to use it here as the
>   * address of the instruction where we might get an exception at.
>   */
> @@ -120,7 +120,7 @@ static inline u64 xfeatures_mask_independent(void)
>                      "\n"                                               \
>                      "xor %[err], %[err]\n"                             \
>                      "3:\n"                                             \
> -                    _ASM_EXTABLE_TYPE_REG(661b, 3b, EX_TYPE_EFAULT_REG, %[err]) \
> +                    _ASM_EXTABLE_TYPE_REG(771b, 3b, EX_TYPE_EFAULT_REG, %[err]) \
>                      : [err] "=r" (err)                                 \
>                      : "D" (st), "m" (*st), "a" (lmask), "d" (hmask)    \
>                      : "memory")
> --
> 2.43.0
>
>

Just add a label at the start of this macro, so it doesn't depend on
the internal labels of ALTERNATIVE().  Something like:
    asm volatile("1:" ALTERNATIVE_3(XSAVE, \
    ...
     _ASM_EXTABLE_TYPE_REG(1b, 3b, EX_TYPE_EFAULT_REG, %[err]) \
    ...


Brian Gerst