linux-kernel - Re: [PATCH 3/3] iommu: Disable passthrough mode when SME is active

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Message-ID: <20190809203208.GB1213@8bytes.org>
Date:   Fri, 9 Aug 2019 22:32:08 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     "Lendacky, Thomas" <Thomas.Lendacky@....com>
Cc:     "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>,
        "bp@...en8.de" <bp@...en8.de>, Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 3/3] iommu: Disable passthrough mode when SME is active

Hey Tom,

On Fri, Aug 09, 2019 at 04:50:48PM +0000, Lendacky, Thomas wrote:
> On 8/9/19 10:22 AM, Joerg Roedel wrote:
> > +	if ((iommu_def_domain_type == IOMMU_DOMAIN_IDENTITY) &&
> > +	    sme_active()) {
> > +		pr_info("SME detected - Disabling default IOMMU passthrough\n");
> > +		iommu_def_domain_type = IOMMU_DOMAIN_DMA;
> 
> Should this also clear the iommu_pass_through variable (the one set by the
> iommu kernel parameter in arch/x86/kernel/pci-dma.c)?

This code is used on different architectures, so I can't cleanly access
architecture specific variables here.

> I guess this is more applicable to the original patchset that created the
> CONFIG_IOMMU_DEFAULT_PASSTHROUGH option, but should the default
> passthrough support be modified so that you don't have to specify multiple
> kernel parameters to change it?
> 
> Right now, if CONFIG_IOMMU_DEFAULT_PASSTHROUGH is set to yes, you can't
> just specify iommu=nopt to enable the IOMMU. You have to also specify
> iommu.passthrough=0. Do we want to fix that so that just specifying
> iommu=nopt or iommu.passthrough=0 does what is needed?

Yeah, that is currently a mess and I think cleaning that up is at least
partly in the scope of this patch-set. I'll look into that next week.


Regards,

	Joerg