linux-kernel - Re: [PATCH V2 3/3] Adding device_dma_parameters->offset_preserve

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Date:   Mon, 1 Feb 2021 13:22:45 -0800
From:   Jianxiong Gao <jxgao@...gle.com>
To:     Keith Busch <kbusch@...nel.org>
Cc:     Erdem Aktas <erdemaktas@...gle.com>, Marc Orr <marcorr@...gle.com>,
        Christoph Hellwig <hch@....de>, m.szyprowski@...sung.com,
        Robin Murphy <robin.murphy@....com>,
        gregkh@...uxfoundation.org, Saravana Kannan <saravanak@...gle.com>,
        heikki.krogerus@...ux.intel.com, rafael.j.wysocki@...el.com,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        dan.j.williams@...el.com, bgolaszewski@...libre.com,
        jroedel@...e.de, iommu@...ts.linux-foundation.org,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, axboe@...com,
        sagi@...mberg.me, linux-nvme@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 3/3] Adding device_dma_parameters->offset_preserve_mask
 to NVMe driver.

> Why is this setting being done and undone on each IO? Wouldn't it be
> more efficient to set it once during device initialization?
>
> And more importantly, this isn't thread safe: one CPU may be setting the
> device's dma alignment mask to 0 while another CPU is expecting it to be
> NVME_CTRL_PAGE_SIZE - 1.

 I was having trouble getting the OS booted when setting it once during
 initialization. However when I rebased to the latest rc6 this morning it
 seems to be working with setting the mask on probe. I am still testing out
 and will appreciate any idea what may cause the nvme driver to fail
 with a single mask.
-- 
Jianxiong Gao