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

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Message-ID: <79b26dac-b507-1c05-b499-784ca6ee3db0@suse.com>
Date:   Fri, 9 Jun 2023 17:38:28 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>,
        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 07.06.23 15:12, Christoph Hellwig wrote:
> 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?

As long as above mentioned check of the E820 map is done, yes.

If you want I can send a diff to be folded into your patch on Monday.

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

Would be nice.


Juergen

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