Re: [RFC][PATCH 1/2] mm/vmalloc: Add IO mapping space reused interface.

Richard Lee
2014-05-13T06:21:26Z

On Tue, May 13, 2014 at 11:13 AM, Rob Herring <robherring2@gmail.com> wrote:
> On Sun, May 11, 2014 at 9:19 PM, Richard Lee <superlibj8301@gmail.com> wrote:
>> For the IO mapping, for the same physical address space maybe
>> mapped more than one time, for example, in some SoCs:
>> 0x20000000 ~ 0x20001000: are global control IO physical map,
>> and this range space will be used by many drivers.
>
> What address or who the user is isn't really relevant.
>
>> And then if each driver will do the same ioremap operation, we
>> will waste to much malloc virtual spaces.
>
> s/malloc/vmalloc/
>
>>
>> This patch add the IO mapping space reusing interface:
>> - find_vm_area_paddr: used to find the exsit vmalloc area using
>
> s/exsit/exist/
>

Yes, see the next version.

[...]
>> +{
>> + struct vmap_area *va;
>> +
>> + va = find_vmap_area((unsigned long)addr);
>> + if (!va || !(va->flags & VM_VM_AREA) || !va->vm)
>> + return 1;
>> +
>> + if (va->vm->used <= 1)
>> + return 1;
>> +
>> + --va->vm->used;
>
> What lock protects this? You should use atomic ops here.
>

Yes, it is.

[...]
>> + if (!(flags & VM_IOREMAP))
>> + return NULL;
>> +
>> + rcu_read_lock();
>> + list_for_each_entry_rcu(va, &vmap_area_list, list) {
>> + phys_addr_t phys_addr;
>> +
>> + if (!va || !(va->flags & VM_VM_AREA) || !va->vm)
>> + continue;
>> +
>> + phys_addr = va->vm->phys_addr;
>> +
>> + if (paddr < phys_addr || paddr + size > phys_addr + va->vm->size)
>> + continue;
>> +
>> + *offset = paddr - phys_addr;
>> +
>> + if (va->vm->flags & VM_IOREMAP && va->vm->size >= size) {
>> + va->vm->used++;
>
> What lock protects this? It looks like you are modifying this with
> only a rcu reader lock.

I'll try to use the proper lock ops for this later.

Thanks very much,

Richard

>
>> + rcu_read_unlock();
>> + return va->vm;
>> + }
>> + }
>> + rcu_read_unlock();
>> +
>> + return NULL;
>> +}
>> +
>> /**
>> * find_vm_area - find a continuous kernel virtual area
>> * @addr: base address
>> --
>> 1.8.4
>>
>>
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