[PATCH] arm: dma-mapping: Fix mapping size value

[Ritesh Harjani]

In explaining the issue below, made a mistake of taking PAGE_SIZE
instead of PAGE_SHIFT (mistake mentioned inline).
Although numerical values and patch is correct.


On Sat, Apr 19, 2014 at 4:49 PM, Ritesh Harjani
<ritesh.harjani at gmail.com> wrote:
> I am finding an oops after following commit. I am on 3.10.30 kernel but applied
> all the latest patches from arch/arm/mm/dma-mapping.c
>
> I added some debug logs to see what is the error, on which I found that we are
> incorrectly setting mapping->size value.
> Please take a look at this and correct me if I am wrong here.
>
> FAULTY COMMIT:
> commit 68efd7d2fb32c2606f1da318b6a851
> d933813f27
> Author: Marek Szyprowski <m.szyprowski at samsung.com>
> Date:   Tue Feb 25 13:01:09 2014 +0100
>
>     arm: dma-mapping: remove order parameter from arm_iommu_create_mapping()
>
>
> OOPS LOGS:
> [26.898145] __alloc_iova#LINE: 1097 start = 0x3500
> [26.898159] __alloc_iova#LINE:1136 iova = 0x53500000
> [26.898170] __alloc_iova#LINE:1138 mapping->base= 0x50000000
> [26.898181] __alloc_iova#LINE:1140 mapping->size = 0x1000000, i = 0
> [26.924442] __free_iova, bitmap_index = 3
>
> [Ritesh]: bitmap_index should be 0 for address 0x53500000. see in alloc_iova
> above.
>
> [26.924454] __free_iova,addr = 0x53500000
> [26.924463] __free_iova,mapping->base = 0x50000000
> [26.924472] __free_iova,mapping->size = 0x1000000
> [26.924482] __free_iova,bitmap_base = 0x53000000
> [26.924490] __free_iova, start = 0x500
>
> [Ritesh]: start should be 0x3500 for address 0x53500000. see in alloc_iova
> above.
>
> [26.924533] Unable to handle kernel NULL pointer dereference at virtual
> address 000000a0
> [26.924543] pgd = e7a84000
> [26.924558] [000000a0] *pgd=00000000
> [26.924572] Internal error: Oops: 5 [#1] PREEMPT SMP ARM
> [26.924598] Modules linked in:
> [26.924613] CPU: 1 PID: 2263 Comm: BufferLiberator Not tainted 3.10.30+
> #144
> [26.924624] task: e7370a40 ti: e6e06000 task.ti: e6e06000
> [26.924644] PC is at bitmap_clear+0x48/0xd0
> [26.924659] LR is at __iommu_remove_mapping+0x130/0x164
> [26.924673] pc : [<c02d0814>]    lr : [<c001bd30>]    psr: 20000093
> [26.924673] sp : e6e07e20  ip : ffffffff  fp : e6e07e3c
> [26.924682] r10: 00000500  r9 : c1333ea8  r8 : 80000013
> [26.924692] r7 : ffffffff  r6 : 00000321  r5 : 000000a0  r4 : 00000028
> [26.924707] r3 : 00000000  r2 : 00000341  r1 : 00000500  r0 : 00000000
> [26.924730] Flags: nzCv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment
> user
> [26.924742] Control: 10c5387d  Table: 77a8406a  DAC: 00000015
>
>
> See below on how this is wrong:
>
> here iova_base = 0x50000000
> iova_size = 0x20000000
> => bits needed to map = 131072.
>         => bitmap_size = 0x4000
>         since bitmap_size > PAGE_SIZE
>         => bitmap_size = PAGE_SIZE,  extensions = 4;
>
> Now, mapping->size is currently set as bitmap_size << PAGE_SHIFT.
>         =>mapping->size = 0x1000000.
> mapping->size is the IOVA size, which one bitmap can address.
>
> Now mapping->size * extensions should be size (0x20000000).
> which is not true, => our bitmap_size is set wrong.
>
> it should be (mapping->bits << PAGE_SIZE) or say

It should be PAGE_SHIFT here.
> (BITS_PER_BYTE * bitmap_size << PAGE_SIZE)

It should be PAGE_SHIFT here.

>         => (8 * 0x1000) << 12) = 0x8000000
> With this IOVA_SIZE = extensions * mapping->size = 0x20000000
>
>
>
> PATCH:
>
> Currently mapping->size is wrongly set resulting
> in OOPS (atleast we see OOPS with extension 4).
>
> Fix this.
>
> Signed-off-by: Ritesh Harjani <ritesh.harjani at gmail.com>
> ---
>  arch/arm/mm/dma-mapping.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index f62aa06..d1701a2 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -1963,8 +1963,8 @@ arm_iommu_create_mapping(struct bus_type *bus,
> dma_addr_t base, size_t size)
>         mapping->nr_bitmaps = 1;
>         mapping->extensions = extensions;
>         mapping->base = base;
> -       mapping->size = bitmap_size << PAGE_SHIFT;
>         mapping->bits = BITS_PER_BYTE * bitmap_size;
> +       mapping->size = mapping->bits << PAGE_SHIFT;
>
>         spin_lock_init(&mapping->lock);
>
> --
> 1.8.1.3