linux-kernel - Re: [PATCH v3] swiotlb: Adjust SWIOTBL bounce buffer size for SEV guests.

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Date:   Fri, 6 Nov 2020 19:24:24 +0100
From:   Christoph Hellwig <hch@....de>
To:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:     Ashish Kalra <ashish.kalra@....com>, hch@....de,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        x86@...nel.org, luto@...nel.org, peterz@...radead.org,
        dave.hansen@...ux-intel.com, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, brijesh.singh@....com,
        Thomas.Lendacky@....com, ssg.sos.patches@....com
Subject: Re: [PATCH v3] swiotlb: Adjust SWIOTBL bounce buffer size for SEV
 guests.

On Thu, Nov 05, 2020 at 02:06:49PM -0500, Konrad Rzeszutek Wilk wrote:
> .
> > > Right, so I am wondering if we can do this better.
> > > 
> > > That is you are never going to get any 32-bit devices with SEV right? That
> > > is there is nothing that bounds you to always use the memory below 4GB?
> > > 
> > 
> > We do support 32-bit PCIe passthrough devices with SEV.
> 
> Ewww..  Which devices would this be?

There is still some new broken shit like that that keeps appearing.
GPU is pretty famouts for supporting less than 64-bit addressing,
even if it isn't all the way down to 32-bit.