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From:   Jianxiong Gao <jxgao@google.com>
Date:   Mon, 1 Feb 2021 13:22:45 -0800
Message-ID: <CAMGD6P1_cs1W8jMt7Sz6broDdnFNPrxbiZW-JZ+GAtg5aoTdOQ@mail.gmail.com>
Subject: Re: [PATCH V2 3/3] Adding device_dma_parameters->offset_preserve_mask
 to NVMe driver.
To:     Keith Busch <kbusch@kernel.org>
Cc:     Erdem Aktas <erdemaktas@google.com>, Marc Orr <marcorr@google.com>,
        Christoph Hellwig <hch@lst.de>, m.szyprowski@samsung.com,
        Robin Murphy <robin.murphy@arm.com>,
        gregkh@linuxfoundation.org, Saravana Kannan <saravanak@google.com>,
        heikki.krogerus@linux.intel.com, rafael.j.wysocki@intel.com,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        dan.j.williams@intel.com, bgolaszewski@baylibre.com,
        jroedel@suse.de, iommu@lists.linux-foundation.org,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, axboe@fb.com,
        sagi@grimberg.me, linux-nvme@lists.infradead.org,
        linux-kernel@vger.kernel.org
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> 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