linux-kernel - Re: [PATCH 2/4] x86: always initialize xen-swiotlb when xen-pcifront is enabling

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Message-ID: <20230607131257.GB19206@lst.de>
Date:   Wed, 7 Jun 2023 15:12:57 +0200
From:   Christoph Hellwig <hch@....de>
To:     Juergen Gross <jgross@...e.com>
Cc:     Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>, Christoph Hellwig <hch@....de>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Ben Skeggs <bskeggs@...hat.com>,
        Karol Herbst <kherbst@...hat.com>,
        Lyude Paul <lyude@...hat.com>, xen-devel@...ts.xenproject.org,
        iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
        nouveau@...ts.freedesktop.org
Subject: Re: [PATCH 2/4] x86: always initialize xen-swiotlb when
 xen-pcifront is enabling

On Mon, May 22, 2023 at 10:37:09AM +0200, Juergen Gross wrote:
> In normal cases PCI passthrough in PV guests requires to start the guest
> with e820_host=1. So it should be rather easy to limit allocating the
> 64MB in PV guests to the cases where the memory map has non-RAM regions
> especially in the first 1MB of the memory.
>
> This will cover even hotplug cases. The only case not covered would be a
> guest started with e820_host=1 even if no PCI passthrough was planned.
> But this should be rather rare (at least I hope so).

So is this an ACK for the patch and can we go ahead with it?

(I'd still like to merge swiotlb-xen into swiotlb eventually, but it's
probably not going to happen this merge window)