Re: [PATCH v2] iommu/iova: Reset max32_alloc_size after cleaning

[<yf.wang@mediatek.com>]

From: yf.wang@mediatek.com <yf.wang@medaitek.com>

On Thu, 2022-03-03 at 07:52 +0800, Miles Chen wrote:
> Thanks for your explanation.
> 
> YF showed me some numbers yesterday and maybe we can have a further
> discussion in that test case. (It looks like that some iovas are
> freed but
> their pfn_lo(s) are less than cached_iova->pfn_lo, so
> max32_alloc_size is not
> reset. So there are enought free iovas but the allocation still
> failed)
> 
> __cached_rbnode_delete_update(struct iova_domain *iovad, struct iova
> *free)
> {
>       struct iova *cached_iova;
> 
>       cached_iova = to_iova(iovad->cached32_node);
>       if (free == cached_iova ||
>               (free->pfn_hi < iovad->dma_32bit_pfn &&
>                free->pfn_lo >= cached_iova->pfn_lo)) {
>               iovad->cached32_node = rb_next(&free->node);
>               iovad->max32_alloc_size = iovad->dma_32bit_pfn;
>       }
>       ...
> }
> 
> Hi YF,
> Could your share your observation of the iova allocation failure you
> hit?
> 
> Thanks,
> Miles

Hi Miles & Robin,

The scenario we encountered in our actual test:
An iova domain with a 3GB iova region (0x4000_0000~0x1_0000_0000),
only alloc iova total size 614788KB), then alloc iova size=0x731f000
fail, and then the retry mechanism is free 300 cache iova at first,
and then retry still fail, the reason for fail is blocked by the
check condition (size >= iovad->max32_alloc_size) and goto iova32_full
directly.

Why is no reset max32_alloc_size in __cached_rbnode_delete_update?
Because of the pfn_lo of the freed cache iova is smaller than the
current cached32_node's pfn_lo (free->pfn_lo < cached_iova->pfn_lo),
so will not execute (iovad->max32_alloc_size = iovad->dma_32bit_pfn),
is blocked by the check condition (free->pfn_lo >= cached_iova-
>pfn_lo).

The issue observed during stress testing, when alloc fail reset
max32_alloc_size to retry can help to allocate iova to those lower
addresses.


The following is the actual stress test log dump: 
('pfn_lo', 'size' and 'pfn_hi' has iova_shift in dump log)
size:                 0x731f000
max32_alloc_size:     0x731f000
cached_iova:          0xffffff814751a1c0
cached_iova->pfn_lo:  0xf3500000
cached_iova->pfn_hi:  0xf35ff000

1.__alloc_and_insert_iova_range_fail
[name:iova&]__alloc_and_insert_iova_range_fail:
iovad:0xffffff80d5be2808
  {granule:0x1000, start_pfn:0x40000, dma_32bit_pfn:0x100000,
  max32_alloc_size:0x731f},size:0x731f

2.dump all iova nodes of rbtree, contain cached iova:
[name:iova&]dump_iova_rbtree start, iovad:0xffffff80d5be2808
  {rbroot:0xffffff814751a4c0, cached_node:0xffffff80d5be2860,
  cached32_node:0xffffff814751a1c0, granule:0x1000, start_pfn:0x40000,
  dma_32bit_pfn:0x100000, max32_alloc_size:0x731f}

('pfn_lo', 'size' and 'pfn_hi' has iova_shift in dump log)
[name:iova&]index    iova_object       pfn_lo     size       pfn_hi
[name:iova&]  1 0xffffff814751ae00  0x40800000  0x4c9000     0x40cc8000
[name:iova&]  2 0xffffff807c960880  0x40d00000  0xc4000      0x40dc3000
  ...322 lines of log are omitted here...
[name:iova&]325 0xffffff814751a1c0  0xf3500000  0x100000     0xf35ff000
[name:iova&]326 0xffffff8004552080  0xf3600000  0x100000     0xf36ff000
[name:iova&]327 0xffffff80045524c0  0xf3700000  0xbc000      0xf37bb000
[name:iova&]328 0xffffff814751a700  0xf3800000  0x265000     0xf3a64000
[name:iova&]329 0xffffff8004552180  0xf3c00000  0xa13000     0xf4612000
[name:iova&]330 0xffffff80c1b3eb40  0xf4800000  0xb400000    0xffbff000
[name:iova&]331 0xffffff80d6e0b580  0xffcff000  0x1000       0xffcff000
[name:iova&]332 0xffffff80c8395140  0xffd00000  0x80000      0xffd7f000
[name:iova&]333 0xffffff80c8395000  0xffde0000  0x20000      0xffdff000
[name:iova&]334 0xffffff80c8395380  0xffe00000  0x80000      0xffe7f000
[name:iova&]335 0xffffff80c8395880  0xffec0000  0x20000      0xffedf000
[name:iova&]336 0xffffff80c83957c0  0xffef9000  0x1000       0xffef9000
[name:iova&]337 0xffffff80c83956c0  0xffefa000  0x1000       0xffefa000
[name:iova&]338 0xffffff80c8395f40  0xffefb000  0x1000       0xffefb000
[name:iova&]339 0xffffff80c8395a80  0xffefc000  0x4000       0xffeff000
[name:iova&]340 0xffffff80c1b3e840  0xfff00000  0x100000     0xfffff000
[name:iova&]341 0xffffff80d5be2860  0xfffffffffffff000 0x1000
0xfffffffffffff000
[name:iova&]dump_iova_rbtree done, iovad:0xffffff80d5be2808,
  count:341, total_size:625876KB

3.alloc fail, flushing rcache and retry.
[name:iova&]alloc_iova_fast, flushing rcache and retry,
  iovad:0xffffff80d5be2808, size:0x731f, limit_pfn:0xfffff

4.retry is executed into the __alloc_and_insert_iova_range function:
[name:iova&]__alloc_and_insert_iova_range fail goto iova32_full,
  iovad:0xffffff80d5be2808 {granule:0x1000, start_pfn:0x40000,
  dma_32bit_pfn:0x100000, max32_alloc_size:0x731f},size:0x731f

5.dump all iova nodes of rbtree, current caches is already empty:
[name:iova&]dump_iova_rbtree start, iovad:0xffffff80d5be2808
  {rbroot:0xffffff80fe76da80, cached_node:0xffffff80d5be2860,
  cached32_node:0xffffff814751a1c0, granule:0x1000, start_pfn:0x40000,
  dma_32bit_pfn:0x100000, max32_alloc_size:0x731f}

('pfn_lo', 'size' and 'pfn_hi' has iova_shift in dump log)
[name:iova&]index    iova_object       pfn_lo     size       pfn_hi
[name:iova&]  1 0xffffff814751ae00  0x40800000  0x4c9000     0x40cc8000
[name:iova&]  2 0xffffff807c960880  0x40d00000  0xc4000      0x40dc3000
[name:iova&]  3 0xffffff81487ce840  0x40e00000  0x37a000     0x41179000
[name:iova&]  4 0xffffff80fe76d600  0x41200000  0x2400000    0x435ff000
[name:iova&]  5 0xffffff8004552000  0x46800000  0x47e2000    0x4afe1000
[name:iova&]  6 0xffffff807c960a40  0x50200000  0x400000     0x505ff000
[name:iova&]  7 0xffffff818cdb5780  0x50600000  0x265000     0x50864000
[name:iova&]  8 0xffffff814751a440  0x50a00000  0x2ae000     0x50cad000
[name:iova&]  9 0xffffff818cdb5d40  0x50e00000  0x4c9000     0x512c8000
[name:iova&] 10 0xffffff81487cef40  0x51400000  0x1a25000    0x52e24000
[name:iova&] 11 0xffffff818cdb5140  0x53c00000  0x400000     0x53fff000
[name:iova&] 12 0xffffff814751a7c0  0x54000000  0x400000     0x543ff000
[name:iova&] 13 0xffffff80fe76d2c0  0x54500000  0xbc000      0x545bb000
[name:iova&] 14 0xffffff81487ce0c0  0x54600000  0x400000     0x549ff000
[name:iova&] 15 0xffffff80fe76d740  0x54a00000  0xbc000      0x54abb000
[name:iova&] 16 0xffffff8004552440  0x54b00000  0xbc000      0x54bbb000
[name:iova&] 17 0xffffff80fe76db80  0x54c00000  0x47e2000    0x593e1000
[name:iova&] 18 0xffffff818cdb5440  0x65000000  0x400000     0x653ff000
[name:iova&] 19 0xffffff8004552880  0x65400000  0x47e2000    0x69be1000
[name:iova&] 20 0xffffff814751acc0  0x6c7e0000  0x20000      0x6c7ff000
[name:iova&] 21 0xffffff80fe76d700  0x6c800000  0x47e2000    0x70fe1000
//0x70fe1000 - 0xebc00000 = 0x7ac1f000:This free range is large enough
[name:iova&] 22 0xffffff80fe76da80  0xebc00000  0x400000     0xebfff000
[name:iova&] 23 0xffffff80045523c0  0xec000000  0x400000     0xec3ff000
[name:iova&] 24 0xffffff8004552780  0xec400000  0x400000     0xec7ff000
[name:iova&] 25 0xffffff814751a1c0  0xf3500000  0x100000     0xf35ff000
[name:iova&] 26 0xffffff8004552080  0xf3600000  0x100000     0xf36ff000
[name:iova&] 27 0xffffff80045524c0  0xf3700000  0xbc000      0xf37bb000
[name:iova&] 28 0xffffff814751a700  0xf3800000  0x265000     0xf3a64000
[name:iova&] 29 0xffffff8004552180  0xf3c00000  0xa13000     0xf4612000
[name:iova&] 30 0xffffff80c1b3eb40  0xf4800000  0xb400000    0xffbff000
[name:iova&] 31 0xffffff80d6e0b580  0xffcff000  0x1000       0xffcff000
[name:iova&] 32 0xffffff80c8395140  0xffd00000  0x80000      0xffd7f000
[name:iova&] 33 0xffffff80c8395000  0xffde0000  0x20000      0xffdff000
[name:iova&] 34 0xffffff80c8395380  0xffe00000  0x80000      0xffe7f000
[name:iova&] 35 0xffffff80c8395880  0xffec0000  0x20000      0xffedf000
[name:iova&] 36 0xffffff80c83957c0  0xffef9000  0x1000       0xffef9000
[name:iova&] 37 0xffffff80c83956c0  0xffefa000  0x1000       0xffefa000
[name:iova&] 38 0xffffff80c8395f40  0xffefb000  0x1000       0xffefb000
[name:iova&] 39 0xffffff80c8395a80  0xffefc000  0x4000       0xffeff000
[name:iova&] 40 0xffffff80c1b3e840  0xfff00000  0x100000     0xfffff000
[name:iova&] 41 0xffffff80d5be2860  0xfffffffffffff000 0x1000
0xfffffffffffff000
[name:iova&]dump_iova_rbtree done, iovad:0xffffff80d5be2808,
count:41, total_size:614788KB

Thanks,
Yunfei.