Re: [PATCH 1/6] powerpc/mm/32: Use pfn_valid to check if pointer is in RAM

From: christophe leroy <christophe.leroy@c-s.fr>
To: "Jonathan Neuschäfer" <j.neuschaefer@gmx.net>,
	linuxppc-dev@lists.ozlabs.org
Cc: linux-kernel@vger.kernel.org,
	Michael Ellerman <mpe@ellerman.id.au>,
	linux-mm@kvack.org, Joel Stanley <joel@jms.id.au>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Balbir Singh <bsingharora@gmail.com>,
	Guenter Roeck <linux@roeck-us.net>
Subject: Re: [PATCH 1/6] powerpc/mm/32: Use pfn_valid to check if pointer is in RAM
Date: Tue, 20 Feb 2018 18:45:09 +0100	[thread overview]
Message-ID: <0d14cb2c-dd00-d258-cb15-302b2a9d684f@c-s.fr> (raw)
In-Reply-To: <20180220161424.5421-2-j.neuschaefer@gmx.net>

Le 20/02/2018 à 17:14, Jonathan Neuschäfer a écrit :
> The Nintendo Wii has a memory layout that places two chunks of RAM at
> non-adjacent addresses, and MMIO between them. Currently, the allocation
> of these MMIO areas is made possible by declaring the MMIO hole as
> reserved memory and allowing reserved memory to be allocated (cf.
> wii_memory_fixups).
> 
> This patch is the first step towards proper support for discontiguous
> memory on PPC32 by using pfn_valid to check if a pointer points into
> RAM, rather than open-coding the check. It should result in no
> functional difference.
> 
> Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
> ---
>   arch/powerpc/mm/pgtable_32.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
> index d35d9ad3c1cd..b5c009893a44 100644
> --- a/arch/powerpc/mm/pgtable_32.c
> +++ b/arch/powerpc/mm/pgtable_32.c
> @@ -147,7 +147,7 @@ __ioremap_caller(phys_addr_t addr, unsigned long size, unsigned long flags,
>   	 * Don't allow anybody to remap normal RAM that we're using.
>   	 * mem_init() sets high_memory so only do the check after that.
>   	 */
> -	if (slab_is_available() && (p < virt_to_phys(high_memory)) &&
> +	if (slab_is_available() && pfn_valid(__phys_to_pfn(p)) &&

I'm not sure this is equivalent:

high_memory = (void *) __va(max_low_pfn * PAGE_SIZE);
#define ARCH_PFN_OFFSET		((unsigned long)(MEMORY_START >> PAGE_SHIFT))
#define pfn_valid(pfn)		((pfn) >= ARCH_PFN_OFFSET && (pfn) < max_mapnr)
set_max_mapnr(max_pfn);

So in the current implementation it checks against max_low_pfn while 
your patch checks against max_pfn

	max_low_pfn = max_pfn = memblock_end_of_DRAM() >> PAGE_SHIFT;
#ifdef CONFIG_HIGHMEM
	max_low_pfn = lowmem_end_addr >> PAGE_SHIFT;
#endif

Christophe

>   	    !(__allow_ioremap_reserved && memblock_is_region_reserved(p, size))) {
>   		printk("__ioremap(): phys addr 0x%llx is RAM lr %ps\n",
>   		       (unsigned long long)p, __builtin_return_address(0));
> 

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