linux-kernel - Re: [PATCH v3 02/10] swiotlb: Factor out slot allocation and free

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Message-ID: <20190424144532.GA21480@lst.de>
Date:   Wed, 24 Apr 2019 16:45:32 +0200
From:   Christoph Hellwig <hch@....de>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Christoph Hellwig <hch@....de>,
        David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>, ashok.raj@...el.com,
        jacob.jun.pan@...el.com, alan.cox@...el.com, kevin.tian@...el.com,
        mika.westerberg@...ux.intel.com, pengfei.xu@...el.com,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 02/10] swiotlb: Factor out slot allocation and free

On Tue, Apr 23, 2019 at 03:32:16PM +0800, Lu Baolu wrote:
> When we add the bounce buffer between IOVA and physical buffer, the
> bounced buffer must starts from the same offset in a page, otherwise,
> IOMMU can't work here.

Why?  Even with the odd hardware descriptors typical in Intel land that
only allow offsets in the first page, not the following ones, having
a zero offset where we previously had one should be fine.