lkml.org 
[lkml]   [2022]   [Aug]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v2] swiotlb: avoid potential left shift overflow
From
Date


On 8/19/22 6:42 PM, Chao Gao wrote:
> On Fri, Aug 19, 2022 at 06:44:05AM -0700, Dongli Zhang wrote:
>> I also encountered this when sending out another version of the 64-bit swiotlb.
>>
>> https://urldefense.com/v3/__https://lore.kernel.org/all/20220609005553.30954-8-dongli.zhang@oracle.com/__;!!ACWV5N9M2RV99hQ!O-2m8d_6yG-OJx1eoiF-wmpJy13HaSz884huJjbeRA9tUdXnUbWsD34MAoY21pSYMdS8tKOM0_7teFvOa3w$
>>
>> Unfortunately, I could not find an environment (e.g., powerpc) to allocate more
>> than 4G until swiotlb supports 64-bit.
>>
>> Although xen supports 64-bit, but the hypervisor side limits the max to < 4G.
>
> Sorry. I didn't notice your series before. I agree that the overflow
> isn't an issue if swiotlb size cannot be larger than 4GB. That's why
> I said the overflow is a potential issue.
>
> In an internal effort to measure the impact of swiotlb size to IO
> performance of confidential VM (e.g., TDX VM), we simply added
> SWIOTLB_ANY to the default io_tlb_mem to lift the restriction on swiotlb
> size. Then we hit this issue and worked out this fix. I posted this
> fix because I think the fix by itself is helpful because it removes the
> implicit dependency of the left-shift in slot_addr() on swiotlb size and
> then someone trying to lift the size limitation won't hit the same issue.
>

Thank you very much for the explanation! I was just curious how to test this
without code modification or powerpc hardware.

Although my RB may not count much:

Reviewed-by: Dongli Zhang <dongli.zhang@oracle.com>

Dongli Zhang

\
 
 \ /
  Last update: 2022-08-20 04:51    [W:0.047 / U:0.196 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site