linux-kernel - Re: [PATCH v6 2/6] iommufd: Add IOMMU_HWPT

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Message-ID: <e36e856a-8d4c-4cc2-a5db-cf00673a9bf7@linux.intel.com>
Date:   Tue, 21 Nov 2023 13:02:49 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Yi Liu <yi.l.liu@...el.com>, joro@...tes.org,
        alex.williamson@...hat.com, jgg@...dia.com, kevin.tian@...el.com,
        robin.murphy@....com
Cc:     baolu.lu@...ux.intel.com, cohuck@...hat.com, eric.auger@...hat.com,
        nicolinc@...dia.com, kvm@...r.kernel.org, mjrosato@...ux.ibm.com,
        chao.p.peng@...ux.intel.com, yi.y.sun@...ux.intel.com,
        peterx@...hat.com, jasowang@...hat.com,
        shameerali.kolothum.thodi@...wei.com, lulu@...hat.com,
        suravee.suthikulpanit@....com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        zhenzhong.duan@...el.com, joao.m.martins@...cle.com,
        xin.zeng@...el.com, yan.y.zhao@...el.com
Subject: Re: [PATCH v6 2/6] iommufd: Add IOMMU_HWPT_INVALIDATE

On 11/17/23 9:07 PM, Yi Liu wrote:
> In nested translation, the stage-1 page table is user-managed but cached
> by the IOMMU hardware, so an update on present page table entries in the
> stage-1 page table should be followed with a cache invalidation.
> 
> Add an IOMMU_HWPT_INVALIDATE ioctl to support such a cache invalidation.
> It takes hwpt_id to specify the iommu_domain, and a multi-entry array to
> support multiple invalidation requests in one ioctl.
> 
> Check cache_invalidate_user op in the iommufd_hw_pagetable_alloc_nested,
> since all nested domains need that.
> 
> Co-developed-by: Nicolin Chen<nicolinc@...dia.com>
> Signed-off-by: Nicolin Chen<nicolinc@...dia.com>
> Signed-off-by: Yi Liu<yi.l.liu@...el.com>
> ---
>   drivers/iommu/iommufd/hw_pagetable.c    | 35 +++++++++++++++++++++++++
>   drivers/iommu/iommufd/iommufd_private.h |  9 +++++++
>   drivers/iommu/iommufd/main.c            |  3 +++
>   include/uapi/linux/iommufd.h            | 35 +++++++++++++++++++++++++
>   4 files changed, 82 insertions(+)
> 
> diff --git a/drivers/iommu/iommufd/hw_pagetable.c b/drivers/iommu/iommufd/hw_pagetable.c
> index 2abbeafdbd22..367459d92f69 100644
> --- a/drivers/iommu/iommufd/hw_pagetable.c
> +++ b/drivers/iommu/iommufd/hw_pagetable.c
> @@ -238,6 +238,11 @@ iommufd_hwpt_nested_alloc(struct iommufd_ctx *ictx,
>   		rc = -EINVAL;
>   		goto out_abort;
>   	}
> +	/* Driver is buggy by missing cache_invalidate_user in domain_ops */
> +	if (WARN_ON_ONCE(!hwpt->domain->ops->cache_invalidate_user)) {
> +		rc = -EINVAL;
> +		goto out_abort;
> +	}
>   	return hwpt_nested;

The WARN message here may cause kernel regression when users bisect
issues. Till this patch, there are no drivers support the
cache_invalidation_user callback yet.

Best regards,
baolu