linux-kernel - Re: [RFC PATCH 1/5] x86/xen: disable swiotlb for xen pvh

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Message-ID: <ea0e3852-87ba-984b-4010-5eeac3d6c507@suse.com>
Date:   Mon, 13 Mar 2023 09:56:55 +0100
From:   Jan Beulich <jbeulich@...e.com>
To:     Huang Rui <ray.huang@....com>
Cc:     Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        Stewart Hildebrand <Stewart.Hildebrand@....com>,
        Xenia Ragiadakou <burzalodowa@...il.com>,
        Honglei Huang <honglei1.huang@....com>,
        Julia Zhang <julia.zhang@....com>,
        Chen Jiqian <Jiqian.Chen@....com>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Roger Pau Monné <roger.pau@...rix.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org
Subject: Re: [RFC PATCH 1/5] x86/xen: disable swiotlb for xen pvh

On 12.03.2023 13:01, Huang Rui wrote:
> Xen PVH is the paravirtualized mode and takes advantage of hardware
> virtualization support when possible. It will using the hardware IOMMU
> support instead of xen-swiotlb, so disable swiotlb if current domain is
> Xen PVH.

But the kernel has no way (yet) to drive the IOMMU, so how can it get
away without resorting to swiotlb in certain cases (like I/O to an
address-restricted device)?

Jan