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Subject: Re: [PATCH] swiotlb-xen: override common mmap and get_sgtable dma ops
To:     Roman Skakun <rm.skakun@gmail.com>
Cc:     Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        xen-devel@lists.xenproject.org, iommu@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>,
        Volodymyr Babchuk <volodymyr_babchuk@epam.com>,
        Roman Skakun <roman_skakun@epam.com>,
        Andrii Anisov <andrii_anisov@epam.com>
References: <20210611095528.9230-1-roman_skakun@epam.com>
 <855a58e2-1e03-4763-cb56-81367b73762c@oracle.com>
 <CADu_u-MqALJkG8RJHrr65vC_sHu-UyvCGwwUfaBong0eir5+hQ@mail.gmail.com>
From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
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Date:   Mon, 14 Jun 2021 11:45:46 -0400
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On 6/14/21 8:47 AM, Roman Skakun wrote:
> Hey, Boris!
> Thanks for the review.
>
> I have an additional question about current implementation that disturbed me.
> I think, that we can have cases when mapped memory can not be
> physically contiguous.
> In order to proceed this correctly need to apply some additional steps
> to current implementation as well.
>
> In mmap() :
> 1. Is the memory region physically contiguous?
> 2. Remap multiple ranges if it is not.
>
> In get_sgtable() :
> 1. Is the memory region physically contiguous?
> 2. Create sgt that will be included multiple contiguous ranges if it is not.
>
> What do you think about it?


We make sure that we allocate contiguous memory in xen_swiotlb_alloc_coherent().


-boris