linux-kernel - Re: [PATCH] swiotlb: set IO TLB segment size via cmdline

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Message-ID: <ece0bbcf-2be8-e655-b164-b39b5d535c63@suse.com>
Date:   Fri, 17 Sep 2021 11:52:10 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Roman Skakun <rm.skakun@...il.com>
Cc:     Andrii Anisov <andrii_anisov@...m.com>,
        Roman Skakun <roman_skakun@...m.com>,
        Jonathan Corbet <corbet@....net>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Maciej W. Rozycki" <macro@...am.me.uk>,
        Muchun Song <songmuchun@...edance.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Mike Rapoport <rppt@...nel.org>, Will Deacon <will@...nel.org>,
        xen-devel@...ts.xenproject.org, linux-mips@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-doc@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH] swiotlb: set IO TLB segment size via cmdline

On 17.09.2021 11:36, Roman Skakun wrote:
> I use Xen PV display. In my case, PV display backend(Dom0) allocates
> contiguous buffer via DMA-API to
> to implement zero-copy between Dom0 and DomU.

Why does the buffer need to be allocated by Dom0? If it was allocated
by DomU, it could use grants to give the backend direct (zero-copy)
access.

Jan