Re: [PATCH RFC] mm: Add debug_virt_to_phys()

[Laura Abbott]

On 11/11/2016 04:44 PM, 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@xxxxxxxxx>
> ---
>  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
>  
>  #define phys_to_virt phys_to_virt
>  static inline void *phys_to_virt(phys_addr_t x)
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index b71086d25195..c9e436b28523 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -186,11 +186,15 @@ extern u64			kimage_voffset;
>   * 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
>  
>  #define phys_to_virt phys_to_virt
>  static inline void *phys_to_virt(phys_addr_t x)
> diff --git a/include/asm-generic/memory_model.h b/include/asm-generic/memory_model.h
> index 5148150cc80b..426085757258 100644
> --- a/include/asm-generic/memory_model.h
> +++ b/include/asm-generic/memory_model.h
> @@ -80,6 +80,10 @@
>  #define page_to_pfn __page_to_pfn
>  #define pfn_to_page __pfn_to_page
>  
> +#ifdef CONFIG_DEBUG_VM
> +unsigned long debug_virt_to_phys(volatile void *address);
> +#endif /* CONFIG_DEBUG_VM */
> +
>  #endif /* __ASSEMBLY__ */
>  
>  #endif
> diff --git a/mm/debug.c b/mm/debug.c
> index 9feb699c5d25..72b2ca9b11f4 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -161,4 +161,19 @@ void dump_mm(const struct mm_struct *mm)
>  	);
>  }
>  
> +#include <asm/memory.h>
> +#include <linux/mm.h>
> +
> +unsigned long debug_virt_to_phys(volatile void *address)
> +{
> +	BUG_ON(is_vmalloc_addr((const void *)address));
> +#if defined(CONFIG_ARM) || defined(CONFIG_ARM64) || defined(CONFIG_UNICORE32) || \
> +	defined(CONFIG_MICROBLAZE)
> +	return __virt_to_phys(address);
> +#else
> +	return virt_to_phys(address);
> +#endif
> +}
> +EXPORT_SYMBOL(debug_virt_to_phys);
> +
>  #endif		/* CONFIG_DEBUG_VM */
> 

is_vmalloc_addr is necessary but not sufficient. This misses
cases like module addresses. The x86 version (CONFIG_DEBUG_VIRTUAL)
bounds checks against the known linear map to catch all cases.
I'm for a generic approach to this if it can catch all cases
that an architecture specific version would catch.

Thanks,
Laura