linux-kernel - Re: [PATCH v2] swiotlb: avoid potential left shift overflow

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Date:   Mon, 22 Aug 2022 04:17:01 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Chao Gao <chao.gao@...el.com>
Cc:     Dongli Zhang <dongli.zhang@...cle.com>,
        linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
        hch@...radead.org, m.szyprowski@...sung.com, robin.murphy@....com,
        jxgao@...gle.com, konrad.wilk@...cle.com
Subject: Re: [PATCH v2] swiotlb: avoid potential left shift overflow

On Sat, Aug 20, 2022 at 09:42:38AM +0800, Chao Gao wrote:
> 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.

SWIOTLB_ANY is used for real, so I think this is a legitimate fix.
I'll apply it.