linux-kernel - Re: [RFC PATCH v1 06/38] iommufd: Add and option to request for bar mapping with IORESOURCE

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Message-ID: <yq5a34afbdtl.fsf@kernel.org>
Date: Tue, 29 Jul 2025 13:58:54 +0530
From: Aneesh Kumar K.V <aneesh.kumar@...nel.org>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: linux-coco@...ts.linux.dev, kvmarm@...ts.linux.dev,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org, aik@....com,
	lukas@...ner.de, Samuel Ortiz <sameo@...osinc.com>,
	Xu Yilun <yilun.xu@...ux.intel.com>,
	Suzuki K Poulose <Suzuki.Poulose@....com>,
	Steven Price <steven.price@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>
Subject: Re: [RFC PATCH v1 06/38] iommufd: Add and option to request for bar
 mapping with IORESOURCE_EXCLUSIVE

Jason Gunthorpe <jgg@...pe.ca> writes:

> On Mon, Jul 28, 2025 at 07:21:43PM +0530, Aneesh Kumar K.V (Arm) wrote:
>> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@...nel.org>
>
> Why would we need this?
>
> I can sort of understand why Intel would need it due to their issues
> with MCE, but ARM shouldn't care either way, should it?
>
> But also why is it an iommufd option? That doesn't seem right..
>
> Jason

This is based on our previous discussion https://lore.kernel.org/all/20250606120919.GH19710@nvidia.com

IIUC, we intend to request the resource in exclusive mode for secure
guests—regardless of whether the platform is Intel or ARM. Could you
help clarify the MCE issue observed on Intel platforms in this context?

-aneesh