linux-kernel - Re: [PATCH 1/1] x86/tboot: Don't disable swiotlb when iommu is forced on

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Message-ID: <20201125155130.GA16839@willie-the-truck>
Date:   Wed, 25 Nov 2020 15:51:30 +0000
From:   Will Deacon <will@...nel.org>
To:     Konrad Rzeszutek Wilk <konrad@...nok.org>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Ning Sun <ning.sun@...el.com>,
        Joerg Roedel <joro@...tes.org>, Borislav Petkov <bp@...en8.de>,
        catalin.marinas@....com, kernel-team@...roid.com, x86@...nel.org,
        tboot-devel@...ts.sourceforge.net,
        Adrian Huang <ahuang12@...ovo.com>,
        iommu@...ts.linux-foundation.org, Ashok Raj <ashok.raj@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] x86/tboot: Don't disable swiotlb when iommu is
 forced on

Hi Konrad,

On Wed, Nov 25, 2020 at 10:41:53AM -0500, Konrad Rzeszutek Wilk wrote:
> On Wed, Nov 25, 2020 at 02:05:15PM +0000, Will Deacon wrote:
> > On Wed, 25 Nov 2020 09:41:24 +0800, Lu Baolu wrote:
> > > After commit 327d5b2fee91c ("iommu/vt-d: Allow 32bit devices to uses DMA
> > > domain"), swiotbl could also be used for direct memory access if IOMMU
> > > is enabled but a device is configured to pass through the DMA translation.
> > > Keep swiotlb when IOMMU is forced on, otherwise, some devices won't work
> > > if "iommu=pt" kernel parameter is used.
> > 
> > Applied to arm64 (for-next/iommu/fixes), thanks!
> > 
> > [1/1] x86/tboot: Don't disable swiotlb when iommu is forced on
> >       https://git.kernel.org/arm64/c/e2be2a833ab5
> 
> But tboot never ran on ARM. It is a Intel specifc.
> 
> I think either me or Thomas should take this patch.

FWIW, I did check with Thomas before I picked it up. I know it looks weird
going via arm64, but that's only because I'm temporarily handling the IOMMU
tree there (including vt-d changes) while Joerg is away. Since this fixes a
vt-d regression, I thought I'd pick it up along with the other IOMMU fixes I
have queued for -rc6.

That said, if you insist, then I can revert it. I'm really only trying to
help here.

Will