linux-kernel - Re: [PATCH v1 1/3] powerpc: Fix eh field when calling lwarx on PPC32

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Date:   Tue, 2 Aug 2022 13:13:15 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Pali Rohár <pali@...nel.org>,
        stable@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/3] powerpc: Fix eh field when calling lwarx on PPC32

Hi!

On Tue, Aug 02, 2022 at 11:02:36AM +0200, Christophe Leroy wrote:
> Commit 9401f4e46cf6 ("powerpc: Use lwarx/ldarx directly instead of
> PPC_LWARX/LDARX macros") properly handled the eh field of lwarx
> in asm/bitops.h but failed to clear it for PPC32 in
> asm/simple_spinlock.h
> 
> So, do as in arch_atomic_try_cmpxchg_lock(), set it to 1 if PPC64
> but set it to 0 if PPC32. For that use IS_ENABLED(CONFIG_PPC64) which
> returns 1 when CONFIG_PPC64 is set and 0 otherwise.
> 
> Reported-by: Pali Rohár <pali@...nel.org>

Reviewed-by: Segher Boessenkool <segher@...nel.crashing.org>

> +	unsigned int eh = IS_ENABLED(CONFIG_PPC64);
>  
>  	token = LOCK_TOKEN;
>  	__asm__ __volatile__(
> -"1:	lwarx		%0,0,%2,1\n\
> +"1:	lwarx		%0,0,%2,%3\n\
>  	cmpwi		0,%0,0\n\
>  	bne-		2f\n\
>  	stwcx.		%1,0,%2\n\
> @@ -59,7 +60,7 @@ static inline unsigned long __arch_spin_trylock(arch_spinlock_t *lock)
>  	PPC_ACQUIRE_BARRIER
>  "2:"
>  	: "=&r" (tmp)
> -	: "r" (token), "r" (&lock->slock)
> +	: "r" (token), "r" (&lock->slock), "i" (eh)
>  	: "cr0", "memory");

That should work yes.  But please note that "n" is prefered if a number
is required (like here), not some other constant, as allowed by "i".

Thanks!


Segher