Re: [RFC PATCH 02/12] iommufd: Add RISC-V IOMMU hwpt and vIOMMU types

From: Jason Gunthorpe <jgg@ziepe.ca>
To: Gong Shuai <gong.shuai@sanechips.com.cn>
Cc: alex@ghiti.fr, andrew.jones@oss.qualcomm.com,
	anup@brainfault.org, aou@eecs.berkeley.edu,
	atish.patra@linux.dev, fangyu.yu@linux.alibaba.com,
	gsh517025@gmail.com, iommu@lists.linux.dev, joro@8bytes.org,
	kevin.tian@intel.com, kvm-riscv@lists.infradead.org,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-riscv@lists.infradead.org, palmer@dabbelt.com,
	pbonzini@redhat.com, pjw@kernel.org, robin.murphy@arm.com,
	seanjc@google.com, tomasz.jeznach@linux.dev, will@kernel.org,
	wu.fei9@sanechips.com.cn, zhao.qingye@sanechips.com.cn
Subject: Re: [RFC PATCH 02/12] iommufd: Add RISC-V IOMMU hwpt and vIOMMU types
Date: Fri, 16 Oct 2026 12:00:49 -0300	[thread overview]
Message-ID: <20261016150049.GG14213@ziepe.ca> (raw)
In-Reply-To: <20261016073020.10119-1-gong.shuai@sanechips.com.cn>

On Fri, Oct 16, 2026 at 03:30:20PM +0800, Gong Shuai wrote:
> Hi Jason,
> 
> Thank you for your review.
> 
> > > +/**
> > > + * struct iommu_hwpt_riscv - RISC-V IOMMU stage-1 page table data
> > > + *			     (IOMMU_HWPT_DATA_RISCV_S1)
> > > + * @tc: Guest device context translation control
> > > + * @iosatp: Guest device context stage-1 root page table pointer
> > > + */
> > > +struct iommu_hwpt_riscv {
> > > +	__aligned_u64 tc;
> > > +	__aligned_u64 iosatp;
> > > +};
> >
> > Like the others you need a spec reference explaining exactly what
> > these fields are.
> 
> I'll add references to the device-context sections of the RISC-V IOMMU
> specification ("Leaf DDT entry", "Device-context fields", "Translation
> control (tc)", and "First-Stage context (fsc)"), and I'll also include
> detailed field information, as ARM does.
> 
> Also, I'll rename the field from iosatp to fsc. It holds iosatp when
> PDTV=0 and process-directory-table pointer (pdtp) when PDTV=1, and the
> two share the same layout, so the name should cover both interpretations
> and the uAPI won't need to change when Process-Directory-Table (PDT)
> support is added.

You might be better off just to have a data[] array of the device
context. I prefer the fields are not parsed out in userspace..

Future specs may add more guest controlled bits and in other places?

Jason

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