linux-kernel - Re: [PATCH v3 0/5] iommu/amd: AVIC Interrupt Remapping Improvements

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Date:   Tue, 6 Jun 2023 07:06:33 -0700
From:   "Suthikulpanit, Suravee" <suravee.suthikulpanit@....com>
To:     linux-kernel@...r.kernel.org, iommu@...ts.linux.dev
Cc:     joro@...tes.org, joao.m.martins@...cle.com,
        alejandro.j.jimenez@...cle.com, boris.ostrovsky@...cle.com,
        jon.grimm@....com, santosh.shukla@....com, vasant.hegde@....com,
        kishon.vijayabraham@....com, jsnitsel@...hat.com
Subject: Re: [PATCH v3 0/5] iommu/amd: AVIC Interrupt Remapping Improvements

Hi Joerg,

Please let me know if you have any other concerns for this series.

Thanks,
Suravee

On 5/30/2023 9:11 PM, Suravee Suthikulpanit wrote:
> For IOMMU AVIC, the IOMMU driver needs to keep track of vcpu scheduling
> changes, and updates interrupt remapping table entry (IRTE) accordingly.
> The IRTE is normally cached by the hardware, which requires the IOMMU
> driver to issue IOMMU IRT invalidation command and wait for completion
> everytime it updates the table.
> 
> Enabling IOMMU AVIC on a large scale system with lots of vcpus and
> VFIO pass-through devices running interrupt-intensive workload,
> it could result in high IRT invalidation rate. In such case, the overhead
> from IRT invalidation could outweigh the benefit of IRTE caching.
> 
> Therefore, introduce a new AMD IOMMU driver option "amd_iommu=irtcachedis"
> to allow disabling IRTE caching, and avoid the need for IRTE invalidation.
> 
> Patch 1,2 prepare the AMD IOMMU driver to support IRT cache disabling.
> Patch 3,4 introduce IRT cache disabling support
> Patch 5 improves the code path in IOMMU driver for updating vcpu scheduling
> for AVIC.
> 
> Thank you,
> Suravee
> 
> Changes from V2
> (https://lore.kernel.org/linux-iommu/rlurmw6n6eyyhtnfr6wva6azur2gvgcrdn4mvykr3nvsosj5py@ieaivyv6cqrv/T/)
> * Added Reviewed-by and Sign-off-by.
> * Patch 4: Reword the commit summary (per Jerry suggestion).
> 
> Changes from V1
> (https://lore.kernel.org/lkml/20230509111646.369661-1-suravee.suthikulpanit@amd.com/T/)
> * Patch 3: Add logic to clean up the IRTE cache disabling
>    and handle kdump code path (per Alejandro)
> 
> Joao Martins (1):
>    iommu/amd: Switch amd_iommu_update_ga() to use modify_irte_ga()
> 
> Suravee Suthikulpanit (4):
>    iommu/amd: Remove the unused struct amd_ir_data.ref
>    iommu/amd: Introduce Disable IRTE Caching Support
>    iommu/amd: Do not Invalidate IRT when IRTE caching is disabled
>    iommu/amd: Improving Interrupt Remapping Table Invalidation
> 
>   .../admin-guide/kernel-parameters.txt         |  1 +
>   drivers/iommu/amd/amd_iommu_types.h           |  7 +-
>   drivers/iommu/amd/init.c                      | 38 +++++++-
>   drivers/iommu/amd/iommu.c                     | 97 ++++++++++---------
>   4 files changed, 94 insertions(+), 49 deletions(-)
>