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Draft: RDMA/core: Fix ib block iterator counter overflow

Kamal Heib requested to merge kheib/centos-stream-9:bz2166720 into main

Bugzilla: https://bugzilla.redhat.com/2166720

commit 0afec5e9cea732cb47014655685a2a47fb180c31
Author: Yonatan Nachum ynachum@amazon.com
Date: Mon Jan 9 13:37:11 2023 +0000

RDMA/core: Fix ib block iterator counter overflow  

When registering a new DMA MR after selecting the best aligned page size  
for it, we iterate over the given sglist to split each entry to smaller,  
aligned to the selected page size, DMA blocks.  

In given circumstances where the sg entry and page size fit certain  
sizes and the sg entry is not aligned to the selected page size, the  
total size of the aligned pages we need to cover the sg entry is >= 4GB.  
Under this circumstances, while iterating page aligned blocks, the  
counter responsible for counting how much we advanced from the start of  
the sg entry is overflowed because its type is u32 and we pass 4GB in  
size. This can lead to an infinite loop inside the iterator function  
because the overflow prevents the counter to be larger  
than the size of the sg entry.  

Fix the presented problem by changing the advancement condition to  
eliminate overflow.  

Backtrace:  
[  192.374329] efa_reg_user_mr_dmabuf  
[  192.376783] efa_register_mr  
[  192.382579] pgsz_bitmap 0xfffff000 rounddown 0x80000000  
[  192.386423] pg_sz [0x80000000] umem_length[0xc0000000]  
[  192.392657] start 0x0 length 0xc0000000 params.page_shift 31 params.page_num 3  
[  192.399559] hp_cnt[3], pages_in_hp[524288]  
[  192.403690] umem->sgt_append.sgt.nents[1]  
[  192.407905] number entries: [1], pg_bit: [31]  
[  192.411397] biter->__sg_nents [1] biter->__sg [0000000008b0c5d8]  
[  192.415601] biter->__sg_advance [665837568] sg_dma_len[3221225472]  
[  192.419823] biter->__sg_nents [1] biter->__sg [0000000008b0c5d8]  
[  192.423976] biter->__sg_advance [2813321216] sg_dma_len[3221225472]  
[  192.428243] biter->__sg_nents [1] biter->__sg [0000000008b0c5d8]  
[  192.432397] biter->__sg_advance [665837568] sg_dma_len[3221225472]  

Fixes: a808273a495c ("RDMA/verbs: Add a DMA iterator to return aligned contiguous memory blocks")  
Signed-off-by: Yonatan Nachum <ynachum@amazon.com>  
Link: https://lore.kernel.org/r/20230109133711.13678-1-ynachum@amazon.com  
Signed-off-by: Leon Romanovsky <leon@kernel.org>

Signed-off-by: Kamal Heib kheib@redhat.com

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