linux-kernel - Re: [RFC PATCH 3/5] drm/amdgpu: set passthrough mode for xen pvh/hvm

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Message-ID: <ZBG9QklWHdt+ZX6U@Air-de-Roger>
Date:   Wed, 15 Mar 2023 13:42:42 +0100
From:   Roger Pau Monné <roger.pau@...rix.com>
To:     Huang Rui <ray.huang@....com>
Cc:     Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org,
        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>
Subject: Re: [RFC PATCH 3/5] drm/amdgpu: set passthrough mode for xen pvh/hvm

On Sun, Mar 12, 2023 at 08:01:55PM +0800, Huang Rui wrote:
> There is an second stage translation between the guest machine address
> and host machine address in Xen PVH/HVM. The PCI bar address in the xen
> guest kernel are not translated at the second stage on Xen PVH/HVM, so

I'm confused by the sentence above, do you think it could be reworded
or expanded to clarify?

PCI BAR addresses are not in the guest kernel, but rather in the
physical memory layout made available to the guest.

Also, I'm unsure why xen_initial_domain() needs to be used in the
conditional below: all PV domains handle addresses the same, so if
it's not needed for a PV dom0 it's likely not needed for a PV domU
either.  Albeit it would help to know more about what
AMDGPU_PASSTHROUGH_MODE implies.

Thanks, Roger.