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

[Rob Herring <robherring2@gmail.com>]

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/

>   the IO physical address.
> - vm_area_is_aready_to_free: before vfree the IO mapped areas
>   using this to do the check that if this area is used by more
>   than one consumer.
>
> Signed-off-by: Richard Lee <superlibj@gmail.com>
> ---
>  include/linux/vmalloc.h |  5 ++++
>  mm/vmalloc.c            | 63 +++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 68 insertions(+)
>
> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> index 4b8a891..2b811f6 100644
> --- a/include/linux/vmalloc.h
> +++ b/include/linux/vmalloc.h
> @@ -34,6 +34,7 @@ struct vm_struct {
>         struct page             **pages;
>         unsigned int            nr_pages;
>         phys_addr_t             phys_addr;
> +       unsigned int            used;
>         const void              *caller;
>  };
>
> @@ -100,6 +101,10 @@ static inline size_t get_vm_area_size(const struct vm_struct *area)
>         return area->size - PAGE_SIZE;
>  }
>
> +extern int vm_area_is_aready_to_free(phys_addr_t addr);
> +struct vm_struct *find_vm_area_paddr(phys_addr_t paddr, size_t size,
> +                                    unsigned long *offset,
> +                                    unsigned long flags);
>  extern struct vm_struct *get_vm_area(unsigned long size, unsigned long flags);
>  extern struct vm_struct *get_vm_area_caller(unsigned long size,
>                                         unsigned long flags, const void *caller);
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index bf233b2..f75b7b3 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1293,6 +1293,7 @@ static void setup_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va,
>         vm->addr = (void *)va->va_start;
>         vm->size = va->va_end - va->va_start;
>         vm->caller = caller;
> +       vm->used = 1;
>         va->vm = vm;
>         va->flags |= VM_VM_AREA;
>         spin_unlock(&vmap_area_lock);
> @@ -1383,6 +1384,68 @@ struct vm_struct *get_vm_area_caller(unsigned long size, unsigned long flags,
>                                   NUMA_NO_NODE, GFP_KERNEL, caller);
>  }
>
> +int vm_area_is_aready_to_free(phys_addr_t addr)

aready is not a word.

> +{
> +       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.

> +
> +       return 0;
> +}
> +
> +/**
> + *     find_vm_area_paddr  -  find a continuous kernel virtual area using the
> + *                     physical addreess.
> + *     @paddr:         base physical address
> + *     @size:          size of the physical area range
> + *     @offset:        the start offset of the vm area
> + *     @flags:         %VM_IOREMAP for I/O mappings
> + *
> + *     Search for the kernel VM area, whoes physical address starting at @paddr,
> + *     and if the exsit VM area's size is large enough, then just return it, or
> + *     return NULL.
> + */
> +struct vm_struct *find_vm_area_paddr(phys_addr_t paddr, size_t size,
> +                                    unsigned long *offset,
> +                                    unsigned long flags)
> +{
> +       struct vmap_area *va;
> +
> +       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.

> +                       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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