linux-kernel - Re: [PATCH RFC] mm: Add debug_virt_to

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Message-ID: <alpine.LFD.2.20.1611112034520.1618@knanqh.ubzr>
Date:   Fri, 11 Nov 2016 20:49:13 -0500 (EST)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Florian Fainelli <f.fainelli@...il.com>
cc:     linux-kernel@...r.kernel.org, Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Chris Brandt <chris.brandt@...esas.com>,
        Pratyush Anand <panand@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Laura Abbott <labbott@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Jerome Marchand <jmarchan@...hat.com>,
        Konstantin Khlebnikov <koct9i@...il.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        "moderated list:ARM PORT" <linux-arm-kernel@...ts.infradead.org>,
        "open list:GENERIC INCLUDE/ASM HEADER FILES" 
        <linux-arch@...r.kernel.org>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>
Subject: Re: [PATCH RFC] mm: Add debug_virt_to_phys()

On Fri, 11 Nov 2016, Florian Fainelli wrote:

> When CONFIG_DEBUG_VM is turned on, virt_to_phys() maps to
> debug_virt_to_phys() which helps catch vmalloc space addresses being
> passed. This is helpful in debugging bogus drivers that just assume
> linear mappings all over the place.
> 
> For ARM, ARM64, Unicore32 and Microblaze, the architectures define
> __virt_to_phys() as being the functional implementation of the address
> translation, so we special case the debug stub to call into
> __virt_to_phys directly.
> 
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> ---
>  arch/arm/include/asm/memory.h      |  4 ++++
>  arch/arm64/include/asm/memory.h    |  4 ++++
>  include/asm-generic/memory_model.h |  4 ++++
>  mm/debug.c                         | 15 +++++++++++++++
>  4 files changed, 27 insertions(+)
> 
> diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
> index 76cbd9c674df..448dec9b8b00 100644
> --- a/arch/arm/include/asm/memory.h
> +++ b/arch/arm/include/asm/memory.h
> @@ -260,11 +260,15 @@ static inline unsigned long __phys_to_virt(phys_addr_t x)
>   * translation for translating DMA addresses.  Use the driver
>   * DMA support - see dma-mapping.h.
>   */
> +#ifndef CONFIG_DEBUG_VM
>  #define virt_to_phys virt_to_phys
>  static inline phys_addr_t virt_to_phys(const volatile void *x)
>  {
>  	return __virt_to_phys((unsigned long)(x));
>  }
> +#else
> +#define virt_to_phys debug_virt_to_phys
> +#endif
[...]

Why don't you do something more like:

 static inline phys_addr_t virt_to_phys(const volatile void *x)
 {
+        debug_virt_to_phys(x);
         return __virt_to_phys((unsigned long)(x));
 }

[...]

static inline void debug_virt_to_phys(const void *address)
{
#ifdef CONFIG_DEBUG_VM
        BUG_ON(is_vmalloc_addr(address));
#endif
}

?


Nicolas