linux-kernel - Re: [RFC PATCH v1 10/38] iommufd/vdevice: Add TSM map ioctl

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Message-ID: <20250728141701.GC26511@ziepe.ca>
Date: Mon, 28 Jul 2025 11:17:01 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: "Aneesh Kumar K.V (Arm)" <aneesh.kumar@...nel.org>
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 10/38] iommufd/vdevice: Add TSM map ioctl

On Mon, Jul 28, 2025 at 07:21:47PM +0530, Aneesh Kumar K.V (Arm) wrote:
> With passthrough devices, we need to make sure private memory is
> allocated and assigned to the secure guest before we can issue the DMA.
> For ARM RMM, we only need to map and the secure SMMU management is
> internal to RMM. For shared IPA, vfio/iommufd DMA MAP/UNMAP interface
> does the equivalent

I'm not really sure what this is about? It is about getting KVM to pin
all the memory and commit it to the RMM so it can be used for DMA?

But it looks really strange to have an iommufd ioctl that just calls a
KVM function. Feeling this should be a KVM function, or a guestmfd
behavior??

I was kind of thinking it would be nice to have a guestmemfd mode that
was "pinned", meaning the memory is allocated and remains almost
always mapped into the TSM's page tables automatically. VFIO using
guests would set things this way.

Jason