linux-kernel - Re: [PATCH 1/7] ubi: block: Refactor sg list processing for highmem

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Date:   Thu, 10 Aug 2023 09:06:10 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Richard Weinberger <richard@....at>
Cc:     linux-mtd@...ts.infradead.org,
        Christoph Hellwig <hch@...radead.org>,
        Stephan Wurm <stephan.wurm@...berle.de>,
        stable@...r.kernel.org, Miquel Raynal <miquel.raynal@...tlin.com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Oliver Neukum <oliver@...kum.org>,
        Ali Akcaagac <aliakc@....de>,
        Jamie Lenehan <lenehan@...bble.org>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Ezequiel Garcia <ezequiel@...guardiasur.com.ar>,
        linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org
Subject: Re: [PATCH 1/7] ubi: block: Refactor sg list processing for highmem

On Thu, Aug 10, 2023 at 06:00:12PM +0200, Richard Weinberger wrote:
> Currently sg_virt() is used while filling the sg list from LEB data.
> This approach cannot work with highmem.
> 
> Refactor ubi_eba_read_leb_sg() to use kmap_atomic() for sg list
> access.
> Since kmap_atomic() disables preempt a bounce buffer is needed.
> kmap_local_page() is not used to allow easy backporting of this patch
> to older kernels.
> 
> The followup patches in this series will switch to kmap_sg()
> and we can remove our own helper and the bounce buffer.

Please just use kmap_local and avoid the bounce buffering.