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Date:   Wed, 8 Sep 2021 08:14:19 +0100
From:   Christoph Hellwig <hch@infradead.org>
To:     Jan Beulich <jbeulich@suse.com>
Cc:     Juergen Gross <jgross@suse.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH 12/12] swiotlb-xen: this is PV-only on x86
Message-ID: <YThiyxG0d2tmCtb+@infradead.org>
References: <588b3e6d-2682-160c-468e-44ca4867a570@suse.com>
 <004feaef-f3bb-e4bb-fb10-f205a9f69f28@suse.com>
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On Tue, Sep 07, 2021 at 02:13:21PM +0200, Jan Beulich wrote:
> The code is unreachable for HVM or PVH, and it also makes little sense
> in auto-translated environments. On Arm, with
> xen_{create,destroy}_contiguous_region() both being stubs, I have a hard
> time seeing what good the Xen specific variant does - the generic one
> ought to be fine for all purposes there. Still Arm code explicitly
> references symbols here, so the code will continue to be included there.

Can the Xen/arm folks look into that?  Getting ARM out of using
swiotlb-xen would be a huge step forward cleaning up some DMA APIs.

> 
> Instead of making PCI_XEN's "select" conditional, simply drop it -
> SWIOTLB_XEN will be available unconditionally in the PV case anyway, and
> is - as explained above - dead code in non-PV environments.
> 
> This in turn allows dropping the stubs for
> xen_{create,destroy}_contiguous_region(), the former of which was broken
> anyway - it failed to set the DMA handle output.

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>