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

Rob Herring
2013-02-05T19:12:58Z

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@lge.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@calxeda.com>

Rob