linux-kernel - Re: [RFC PATCH v2 08/18] iommu/riscv: Use MSI table to enable IMSIC access

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Message-ID: <20250923145251.GP1391379@nvidia.com>
Date: Tue, 23 Sep 2025 11:52:51 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Andrew Jones <ajones@...tanamicro.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, iommu@...ts.linux.dev,
	kvm-riscv@...ts.infradead.org, kvm@...r.kernel.org,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
	zong.li@...ive.com, tjeznach@...osinc.com, joro@...tes.org,
	will@...nel.org, robin.murphy@....com, anup@...infault.org,
	atish.patra@...ux.dev, alex.williamson@...hat.com,
	paul.walmsley@...ive.com, palmer@...belt.com, alex@...ti.fr
Subject: Re: [RFC PATCH v2 08/18] iommu/riscv: Use MSI table to enable IMSIC
 access

On Tue, Sep 23, 2025 at 09:37:31AM -0500, Andrew Jones wrote:
> undergoes a specified translation into an index of the MSI table. For the
> non-virt use case we skip the "composes a new address/data pair, which
> points at the remap table entry" step since we just forward the original
> with an identity mapping. For the virt case we do write a new addr,data
> pair (Patch15) since we need to map guest addresses to host addresses (but
> data is still just forwarded since the RISC-V IOMMU doesn't support data
> remapping). 

You should banish thinking of non-virt/virt from your lexicon. Linux
doesn't work that way, and trying to force it too is a loosing battle.

If you have a remap domain then it should always be remapping. There
is no such idea in Linux as a conditional IRQ domain dependent on
external factors (like how the IOMMU is configured, if the device is
"virt" or not, etc).

Be specific what you mean.

Jason