linux-kernel - Re: [PATCH v5 3/3] ARM: mm: use static_vm for managing static mapped areas

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Date:	Tue, 05 Feb 2013 13:12:51 -0600
From:	Rob Herring <robherring2@...il.com>
To:	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
CC:	Rob Herring <rob.herring@...xeda.com>,
	Russell King <linux@....linux.org.uk>, js1304@...il.com,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5 3/3] ARM: mm: use static_vm for managing static mapped
 areas

On 02/05/2013 12:13 PM, Nicolas Pitre wrote:
> On Tue, 5 Feb 2013, Rob Herring wrote:
> 
>> On 02/04/2013 10:44 PM, Nicolas Pitre wrote:
>>> On Tue, 5 Feb 2013, Joonsoo Kim wrote:
>>>
>>>> A static mapped area is ARM-specific, so it is better not to use
>>>> generic vmalloc data structure, that is, vmlist and vmlist_lock
>>>> for managing static mapped area. And it causes some needless overhead and
>>>> reducing this overhead is better idea.
>>>>
>>>> Now, we have newly introduced static_vm infrastructure.
>>>> With it, we don't need to iterate all mapped areas. Instead, we just
>>>> iterate static mapped areas. It helps to reduce an overhead of finding
>>>> matched area. And architecture dependency on vmalloc layer is removed,
>>>> so it will help to maintainability for vmalloc layer.
>>>>
>>>> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
>>
>> [snip]
>>
>>>> @@ -859,17 +864,12 @@ static void __init pci_reserve_io(void)
>>>>  {
>>>>  	struct vm_struct *vm;
>>>>  	unsigned long addr;
>>>> +	struct static_vm *svm;
>>>>  
>>>> -	/* we're still single threaded hence no lock needed here */
>>>> -	for (vm = vmlist; vm; vm = vm->next) {
>>>> -		if (!(vm->flags & VM_ARM_STATIC_MAPPING))
>>>> -			continue;
>>>> -		addr = (unsigned long)vm->addr;
>>>> -		addr &= ~(SZ_2M - 1);
>>>> -		if (addr == PCI_IO_VIRT_BASE)
>>>> -			return;
>>>> +	svm = find_static_vm_vaddr((void *)PCI_IO_VIRT_BASE);
>>>> +	if (svm)
>>>> +		return;
>>>>
>>>> -	}
>>>>  
>>>>  	vm_reserve_area_early(PCI_IO_VIRT_BASE, SZ_2M, pci_reserve_io);
>>>>  }
>>>
>>> The replacement code is not equivalent.  I can't recall why the original 
>>> is as it is, but it doesn't look right to me.  The 2MB round down 
>>> certainly looks suspicious.
>>
>> The PCI mapping is at a fixed, aligned 2MB mapping. If we find any
>> virtual address within that region already mapped, it is an error.
> 
> Ah, OK.  This wasn't clear looking at the code.
> 
>> We probably should have had a WARN here.
> 
> Indeed.
> 
>>>
>>> The replacement code should be better.  However I'd like you to get an 
>>> ACK from Rob Herring as well for this patch.
>>
>> It doesn't appear to me the above case is handled. The virt addr is
>> checked whether it is within an existing mapping, but not whether the
>> new mapping would overlap an existing mapping. It would be good to check
>> for this generically rather than specifically for the PCI i/o mapping.
> 
> Agreed.  However that is checked already in vm_area_add_early().  
> Therefore the overlap test here is redundant.

Ah, right. In that case:

Acked-by: Rob Herring <rob.herring@...xeda.com>

Rob

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