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Date: Tue, 26 Aug 2025 07:47:46 -0600
From: Keith Busch <kbusch@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Christoph Hellwig <hch@infradead.org>, Keith Busch <kbusch@meta.com>,
	linux-block@vger.kernel.org, linux-nvme@lists.infradead.org,
	axboe@kernel.dk, iommu@lists.linux.dev
Subject: Re: [PATCHv3 1/2] block: accumulate segment page gaps per bio
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 <aKxpSorluMXgOFEI@infradead.org>
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In-Reply-To: <20250826130344.GA32739@lst.de>

On Tue, Aug 26, 2025 at 03:03:44PM +0200, Christoph Hellwig wrote:
> On Mon, Aug 25, 2025 at 08:10:59AM -0600, Keith Busch wrote:
> > 
> > PAGE_SIZEs, iommu granules, and virt boundaries are all power-of-two
> > values, and PAGE_SIZE is always the largest (or tied for largest) of
> > these.
> 
> I just had an offlist conversation with someone trying to make a nvme
> device with a virt boundary larger than PAGE_SIZE work.  No idea
> where that device came from.

Currently, the virtual boundary is always compared to bv_offset, which
is a page offset. If the virtual boundary is larger than a page, then we
need something like "page_to_phys(bv.bv_page) + bv.bv_offset" every
place we need to check against the virt boundary.