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

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Message-ID: <CAHPCO9G8nqVfBXw3ej_Ot8CUkKgVB5QiZtkd9y+JBOBAaeJ7GQ@mail.gmail.com>
Date:	Tue, 13 May 2014 14:21:24 +0800
From:	Richard Lee <superlibj8301@...il.com>
To:	Rob Herring <robherring2@...il.com>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Richard Lee <superlibj@...il.com>
Subject: Re: [RFC][PATCH 1/2] mm/vmalloc: Add IO mapping space reused interface.

On Tue, May 13, 2014 at 11:13 AM, Rob Herring <robherring2@...il.com> wrote:
> On Sun, May 11, 2014 at 9:19 PM, Richard Lee <superlibj8301@...il.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
>>
>>
>> _______________________________________________
>> linux-arm-kernel mailing list
>> linux-arm-kernel@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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