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Message-ID: <45a3ae40-6e59-43b4-ae57-d159bd2b54df@linux.intel.com>
Date: Thu, 5 Sep 2024 15:31:08 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Joerg Roedel <joro@...tes.org>,
Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
Vasant Hegde <vasant.hegde@....com>
Cc: baolu.lu@...ux.intel.com, Jason Gunthorpe <jgg@...dia.com>,
linux-doc@...r.kernel.org, iommu@...ts.linux.dev,
linux-kernel@...r.kernel.org, Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH] iommu/amd: Add kernel parameters to limit V1 page-sizes
On 2024/9/5 15:22, Joerg Roedel wrote:
> From: Joerg Roedel<jroedel@...e.de>
>
> Add two new kernel command line parameters to limit the page-sizes
> used for v1 page-tables:
>
> nohugepages - Limits page-sizes to 4KiB
>
> v2_pgsizes_only - Limits page-sizes to 4Kib/2Mib/1GiB; The
> same as the sizes used with v2 page-tables
>
> This is needed for multiple scenarios. When assigning devices to
> SEV-SNP guests the IOMMU page-sizes need to match the sizes in the RMP
> table, otherwise the device will not be able to access all shared
> memory.
>
> Also, some ATS devices do not work properly with arbitrary IO
> page-sizes as supported by AMD-Vi, so limiting the sizes used by the
> driver is a suitable workaround.
>
> All-in-all, these parameters are only workarounds until the IOMMU core
> and related APIs gather the ability to negotiate the page-sizes in a
> better way.
>
> Signed-off-by: Joerg Roedel<jroedel@...e.de>
> ---
> Documentation/admin-guide/kernel-parameters.txt | 17 +++++++++++------
> drivers/iommu/amd/amd_iommu.h | 1 +
> drivers/iommu/amd/amd_iommu_types.h | 4 ++++
> drivers/iommu/amd/init.c | 8 ++++++++
> drivers/iommu/amd/io_pgtable.c | 2 +-
> 5 files changed, 25 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 09126bb8cc9f..6d6630aec46c 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -333,12 +333,17 @@
> allowed anymore to lift isolation
> requirements as needed. This option
> does not override iommu=pt
> - force_enable - Force enable the IOMMU on platforms known
> - to be buggy with IOMMU enabled. Use this
> - option with care.
> - pgtbl_v1 - Use v1 page table for DMA-API (Default).
> - pgtbl_v2 - Use v2 page table for DMA-API.
> - irtcachedis - Disable Interrupt Remapping Table (IRT) caching.
> + force_enable - Force enable the IOMMU on platforms known
> + to be buggy with IOMMU enabled. Use this
> + option with care.
> + pgtbl_v1 - Use v1 page table for DMA-API (Default).
> + pgtbl_v2 - Use v2 page table for DMA-API.
> + irtcachedis - Disable Interrupt Remapping Table (IRT) caching.
> + nohugepages - Limit page-sizes used for v1 page-tables
> + to 4 KiB.
Intel iommu driver has a similar option 'intel_iommu=sp_off'
sp_off [Default Off]
By default, super page will be supported if Intel IOMMU
has the capability. With this option, super page will
not be supported.
Is it possible to consolidate these two into a single
"iommu.nohugepages=1"?
> + v2_pgsizes_only - Limit page-sizes used for v1 page-tables
> + to 4KiB/2Mib/1GiB.
> +
>
> amd_iommu_dump= [HW,X86-64]
> Enable AMD IOMMU driver option to dump the ACPI table
Thanks,
baolu
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