Messages in this thread | | | Date | Sat, 20 Aug 2022 09:42:38 +0800 | From | Chao Gao <> | Subject | Re: [PATCH v2] swiotlb: avoid potential left shift overflow |
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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://lore.kernel.org/all/20220609005553.30954-8-dongli.zhang@oracle.com/ > >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.
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