Re: [PATCH 5/6] powerpc/64: Only WARN if __pa()/__va() called with bad addresses

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 06/04/2022 à 16:58, Michael Ellerman a écrit :
> We added checks to __pa() / __va() to ensure they're only called with
> appropriate addresses. But using BUG_ON() is too strong, it means
> virt_addr_valid() will BUG when DEBUG_VIRTUAL is enabled.
> 
> Instead switch them to warnings, arm64 does the same.
> 
> Fixes: 4dd7554a6456 ("powerpc/64: Add VIRTUAL_BUG_ON checks for __va and __pa addresses")
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> ---
>   arch/powerpc/include/asm/page.h | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
> index f2c5c26869f1..40a27a56ee40 100644
> --- a/arch/powerpc/include/asm/page.h
> +++ b/arch/powerpc/include/asm/page.h
> @@ -216,6 +216,12 @@ static inline bool pfn_valid(unsigned long pfn)
>   #define __pa(x) ((phys_addr_t)(unsigned long)(x) - VIRT_PHYS_OFFSET)
>   #else
>   #ifdef CONFIG_PPC64
> +
> +#ifdef CONFIG_DEBUG_VIRTUAL
> +#define VIRTUAL_WARN_ON(x)	WARN_ON(x)
> +#else
> +#define VIRTUAL_WARN_ON(x)
> +#endif

Could be:

#define VIRTUAL_WARN_ON(x)	WARN_ON(IS_ENABLED(CONFIG_DEBUG_VIRTUAL) && (x))

>   /*
>    * gcc miscompiles (unsigned long)(&static_var) - PAGE_OFFSET
>    * with -mcmodel=medium, so we use & and | instead of - and + on 64-bit.
> @@ -223,13 +229,13 @@ static inline bool pfn_valid(unsigned long pfn)
>    */
>   #define __va(x)								\
>   ({									\
> -	VIRTUAL_BUG_ON((unsigned long)(x) >= PAGE_OFFSET);		\
> +	VIRTUAL_WARN_ON((unsigned long)(x) >= PAGE_OFFSET);		\
>   	(void *)(unsigned long)((phys_addr_t)(x) | PAGE_OFFSET);	\
>   })
>   
>   #define __pa(x)								\
>   ({									\
> -	VIRTUAL_BUG_ON((unsigned long)(x) < PAGE_OFFSET);		\
> +	VIRTUAL_WARN_ON((unsigned long)(x) < PAGE_OFFSET);		\
>   	(unsigned long)(x) & 0x0fffffffffffffffUL;			\
>   })
>   

Isn't it dangerous to WARN (or BUG) here ? __pa() can be used very early 
during boot, like in prom_init.c

Some other architectures have a __pa_nodebug(). The __pa() does the 
WARN() then calls __pa_nodebug(). Early users call __pa_nodebug() directly.

Christophe