Re: [RFC PATCH 6/7] riscv_cbqri: Assign IOMMU groups to resource groups

From: Drew Fustini <fustini@kernel.org>
To: Zhanpeng Zhang <zhangzhanpeng.jasper@bytedance.com>
Cc: Reinette Chatre <reinette.chatre@intel.com>,
	Ben Horgan <ben.horgan@arm.com>,
	joro@8bytes.org, palmer@dabbelt.com, tony.luck@intel.com,
	tomasz.jeznach@linux.dev, will@kernel.org, robin.murphy@arm.com,
	pjw@kernel.org, aou@eecs.berkeley.edu, alex@ghiti.fr,
	Dave.Martin@arm.com, james.morse@arm.com, babu.moger@amd.com,
	corbet@lwn.net, shuah@kernel.org, jgg@ziepe.ca,
	kevin.tian@intel.com, cuiyunhui@bytedance.com,
	yuanzhu@bytedance.com, iommu@lists.linux.dev,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org,
	x86@kernel.org
Subject: Re: [RFC PATCH 6/7] riscv_cbqri: Assign IOMMU groups to resource groups
Date: Thu, 13 Aug 2026 10:43:33 -0700	[thread overview]
Message-ID: <an4CRRXt44+PhHgy@x1> (raw)
In-Reply-To: <20260714130657.46963-7-zhangzhanpeng.jasper@bytedance.com>

On Tue, Jul 14, 2026 at 09:06:56PM +0800, Zhanpeng Zhang wrote:
> Allow the resctrl devices file to accept iommu_group:<id> tokens on
> RISC-V and map the target resource group's closid and rmid values to
> RCID and MCID.
> 
> Record non-default assignments in an RCU-protected binding list rather
> than inferring membership from hardware IDs, which may be shared. Keep a
> parent reference obtained by numeric group lookup so the binding does not
> keep an empty group's devices kobject active, and prune bindings after
> their group becomes inactive.
> 
> Publish an explicit UPDATING state while hardware changes. Paging-domain
> attachment rejects that transient state. Static FSC=Bare transitions
> preserve the current IDs so a mandatory release-domain attachment cannot
> fail. After the checked group update succeeds, publish the packed IDs. A
> validation failure restores the previous active state without partially
> changing hardware.
> 
> Moving an IOMMU group to the default resource group resets its hardware
> state and removes the software binding. Device contexts created later for
> an assigned group inherit the IDs through the RCU lookup path.
> 
> Signed-off-by: Zhanpeng Zhang <zhangzhanpeng.jasper@bytedance.com>
[..]
> diff --git a/drivers/resctrl/cbqri_iommu.c b/drivers/resctrl/cbqri_iommu.c
> new file mode 100644
> index 000000000000..4086c32546bd
> --- /dev/null
> +++ b/drivers/resctrl/cbqri_iommu.c
[..]
> +#include <asm/qos.h>
> +
> +#define IOMMU_GROUP_TOKEN	"iommu_group:"

I am wondering if maybe this should be parsed at the resctrl layer since
it could be possible for RISC-V and ARM to both use the iommu_group
token. I am hoping that Reinette and the MPAM developrs will add their
prespectives on the the resctrl devices file and at what level the
tokens should be parsed.

Thanks,
Drew

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv