Messages in this thread | | | Subject | Re: [PATCH v2] swiotlb: avoid potential left shift overflow | From | Dongli Zhang <> | Date | Fri, 19 Aug 2022 19:50:12 -0700 |
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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
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