linux-kernel - Re: [PATCH v6] swiotlb: Adjust SWIOTBL bounce buffer size for SEV guests.

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Date:   Mon, 23 Nov 2020 13:43:27 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Ashish Kalra <Ashish.Kalra@....com>, hch@....de,
        tglx@...utronix.de, mingo@...hat.com, 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, jon.grimm@....com, rientjes@...gle.com
Subject: Re: [PATCH v6] swiotlb: Adjust SWIOTBL bounce buffer size for SEV
 guests.

On Mon, Nov 23, 2020 at 07:02:15PM +0100, Borislav Petkov wrote:
> On Mon, Nov 23, 2020 at 12:56:32PM -0500, Konrad Rzeszutek Wilk wrote:
> > This is not going to work for TDX. I think having a registration
> > to SWIOTLB to have this function would be better going forward.
> > 
> > As in there will be a swiotlb_register_adjuster() which AMD SEV
> > code can call at start, also TDX can do it (and other platforms).
> 
> Oh do tell. It doesn't need to adjust size?

I am assuming that TDX is going to have the same exact issue that 
AMD SEV will have.

Are you recommending to have an unified x86 specific callback
where we check if it:

 - CPUID_AMD_SEV or CPUID_INTEL_TDX is set, and
 - No vIOMMU present, then we adjust the size?

> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette