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Date:   Mon, 30 Aug 2021 21:02:23 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     Borislav Petkov <bp@alien8.de>,
        LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [patch 01/10] x86/fpu/signal: Clarify exception handling in
 restore_fpregs_from_user()
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On Mon, Aug 30, 2021 at 10:09:27PM +0200, Thomas Gleixner wrote:

> +++ b/arch/x86/include/asm/fpu/internal.h
> @@ -88,7 +88,11 @@ static inline void fpstate_init_soft(str
>  #endif
>  extern void save_fpregs_to_fpstate(struct fpu *fpu);
>  
> -/* Returns 0 or the negated trap number, which results in -EFAULT for #PF */
> +/*
> + * Returns 0 on success or the negated trap number when the operation
> + * raises an exception (The exception fixup function ex_handler_fault()
> + * stores the trap number in EAX).
> + */
>  #define user_insn(insn, output, input...)				\
>  ({									\
>  	int err;							\
> @@ -199,7 +203,8 @@ static inline void fxsave(struct fxregs_
>  
>  /*
>   * After this @err contains 0 on success or the negated trap number when
> - * the operation raises an exception. For faults this results in -EFAULT.
> + * the operation raises an exception (The exception fixup function
> + * ex_handler_fault() stores the trap number in EAX).
>   */
>  #define XSTATE_OP(op, st, lmask, hmask, err)				\
>  	asm volatile("1:" op "\n\t"					\

Incidentally, why do we bother with negation in those?  Why not have
user_insn(), XSTATE_OP() and kernel_insn_err() return 0 or trap number...