From: Nicolin Chen <nicolinc@nvidia.com>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: Andrew Jones <andrew.jones@oss.qualcomm.com>,
<linux-riscv@lists.infradead.org>, <iommu@lists.linux.dev>,
<linux-kernel@vger.kernel.org>, <tomasz.jeznach@linux.dev>,
<tjeznach@rivosinc.com>, <jgg@ziepe.ca>, <joro@8bytes.org>,
<will@kernel.org>, <robin.murphy@arm.com>, <pjw@kernel.org>,
<palmer@dabbelt.com>, <anup@brainfault.org>, <tglx@kernel.org>,
<kevin.tian@intel.com>, <fangyu.yu@linux.alibaba.com>
Subject: Re: [PATCH v6 09/16] iommu/riscv: Reserve an MSI IOVA window for iommufd
Date: Thu, 15 Oct 2026 12:51:33 -0700 [thread overview]
Message-ID: <atEuxafCLCdZrdR7@nvidia.com> (raw)
In-Reply-To: <179209292716.4133959.2758345963634439485.b4-review@b4>
On Thu, Oct 15, 2026 at 04:35:27PM -0300, Jason Gunthorpe wrote:
> > Reserve one page per possible CPU, sufficient for each supervisor IMSIC
> > page. Use a 16 MiB base instead of the 128 MiB convention used by ARM
> > SMMU. kvmtool places its guest IMSIC at 128 MiB, so with IRQ bypass the
> > domain-wide guest MSI address match can also capture host-delivered
> > MSI writes to the SW MSI window and misdeliver them to the guest.
> >
> > 16 MiB falls in a hole in the current kvmtool and QEMU virt memory maps,
> > away from their guest IMSIC windows and RAM. Keep the window below
> > 4 GiB so devices with 32-bit MSI address registers can use it.
>
> And this is a good reason you should not follow ARM down this mad
> road. Nicolin had some patches to allow userspace to select the SW_MSI
> range instead of using a kernel hard coded value, which becomes a
> sneaky ABI. It would be much better if riscv starts off on the right
> foot instead of continuing this mistake.
It was paused due to lack of an immediate interest:
https://lore.kernel.org/linux-iommu/cover.1760487869.git.nicolinc@nvidia.com/
If riscv wants it, maybe we can give a push.
Nicolin
next prev parent reply other threads:[~2026-10-15 19:52 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-25 15:16 [PATCH v6 00/16] iommu/riscv: Enable MSI remapping, IOMMU_DMA and VFIO Andrew Jones
2026-09-25 15:16 ` [PATCH v6 01/16] iommu/dma: Prepare MSI physical address lists Andrew Jones
2026-10-02 16:21 ` Robin Murphy
2026-10-03 12:03 ` Andrew Jones
2026-10-03 12:10 ` Jason Gunthorpe
2026-09-25 15:16 ` [PATCH v6 02/16] iommufd: Convert struct iommufd_sw_msi_maps to a growable bitmap Andrew Jones
2026-10-15 19:35 ` Jason Gunthorpe
2026-09-25 15:16 ` [PATCH v6 03/16] iommufd: Split software MSI map lookup and allocation Andrew Jones
2026-09-25 15:16 ` [PATCH v6 04/16] iommufd: Bound software MSI mappings to the reserved range Andrew Jones
2026-09-25 15:16 ` [PATCH v6 05/16] iommufd: Prepare software MSI maps for address lists Andrew Jones
2026-09-25 15:16 ` [PATCH v6 06/16] iommufd: Install software MSI map ranges atomically Andrew Jones
2026-09-25 15:16 ` [PATCH v6 07/16] iommufd: Prepare software MSI installation for address lists Andrew Jones
2026-09-28 10:23 ` Andrew Jones
2026-09-25 15:16 ` [PATCH v6 08/16] iommu/dma: Introduce iommu_dma_prepare_msi_list() Andrew Jones
2026-09-25 15:16 ` [PATCH v6 09/16] iommu/riscv: Reserve an MSI IOVA window for iommufd Andrew Jones
2026-10-15 19:35 ` Jason Gunthorpe
2026-10-15 19:51 ` Nicolin Chen [this message]
2026-09-25 15:16 ` [PATCH v6 10/16] irqchip/riscv-imsic: Add MSI address list Andrew Jones
2026-09-25 15:51 ` Anup Patel
2026-10-15 21:33 ` Thomas Gleixner
2026-09-28 3:27 ` Nutty.Liu
2026-09-28 10:20 ` Andrew Jones
2026-10-15 21:32 ` Thomas Gleixner
2026-09-25 15:16 ` [PATCH v6 11/16] irqchip/riscv-imsic: Support IOMMU MSI address lists Andrew Jones
2026-09-25 15:52 ` Anup Patel
2026-09-28 3:18 ` Nutty.Liu
2026-10-15 21:32 ` Thomas Gleixner
2026-09-25 15:16 ` [PATCH v6 12/16] iommu/dma: Enable IOMMU_DMA for 64-bit RISC-V Andrew Jones
2026-09-28 3:17 ` Nutty.Liu
2026-09-25 15:16 ` [PATCH v6 13/16] vfio: enable IOMMU_TYPE1 for RISC-V Andrew Jones
2026-09-25 15:16 ` [PATCH v6 14/16] RISC-V: KVM: Enable KVM_VFIO interfaces on RISC-V arch Andrew Jones
2026-09-25 15:51 ` Anup Patel
2026-09-25 15:16 ` [PATCH v6 15/16] riscv: defconfig: Enable IOMMUFD and VFIO Andrew Jones
2026-09-28 3:17 ` Nutty.Liu
2026-09-25 15:16 ` [PATCH v6 16/16] selftests/vfio: Allow building on RISC-V Andrew Jones
2026-09-28 3:16 ` Nutty.Liu
2026-09-28 10:24 ` [PATCH v6 00/16] iommu/riscv: Enable MSI remapping, IOMMU_DMA and VFIO Andrew Jones
2026-10-15 19:35 ` Jason Gunthorpe
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