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Date:   Tue, 25 Jun 2019 18:22:35 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Damien Le Moal <damien.lemoal@wdc.com>
Cc:     linux-scsi@vger.kernel.org,
        "Martin K . Petersen" <martin.petersen@oracle.com>,
        linux-block@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
        Christoph Hellwig <hch@lst.de>,
        Bart Van Assche <bvanassche@acm.org>
Subject: Re: [PATCH 1/3] block: Allow mapping of vmalloc-ed buffers
Message-ID: <20190625162235.GA9203@lst.de>
References: <20190625024625.23976-1-damien.lemoal@wdc.com> <20190625024625.23976-2-damien.lemoal@wdc.com>
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On Tue, Jun 25, 2019 at 11:46:23AM +0900, Damien Le Moal wrote:
> To allow the SCSI subsystem scsi_execute_req() function to issue
> requests using large buffers that are better allocated with vmalloc()
> rather than kmalloc(), modify bio_map_kern() to allow passing a buffer
> allocated with the vmalloc() function. To do so, simply test the buffer
> address using is_vmalloc_addr() and use vmalloc_to_page() instead of
> virt_to_page() to obtain the pages of vmalloc-ed buffers.

This is broken on architectures with VIVT caches.  You need to flush
and invalidate the caches based on the virtual address on those before
performing DMA operations.