linux-kernel - Re: [PATCH v4 1/2] iommu/sva: Tighten SVA bind API with explicit flags

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Date:   Wed, 12 May 2021 12:18:08 +0200
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        iommu@...ts.linux-foundation.org, Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Christoph Hellwig <hch@...radead.org>,
        Yi Liu <yi.l.liu@...el.com>, Raj Ashok <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Dave Jiang <dave.jiang@...el.com>, wangzhou1@...ilicon.com,
        zhangfei.gao@...aro.org, vkoul@...nel.org
Subject: Re: [PATCH v4 1/2] iommu/sva: Tighten SVA bind API with explicit
 flags

On Mon, May 10, 2021 at 06:25:07AM -0700, Jacob Pan wrote:
> The void* drvdata parameter isn't really used in iommu_sva_bind_device()
> API, the current IDXD code "borrows" the drvdata for a VT-d private flag
> for supervisor SVA usage.
> 
> Supervisor/Privileged mode request is a generic feature. It should be
> promoted from the VT-d vendor driver to the generic code.
> 
> This patch replaces void* drvdata with a unsigned int flags parameter
> and adjusts callers accordingly.
> 
> Link: https://lore.kernel.org/linux-iommu/YFhiMLR35WWMW%2FHu@myrica/
> Suggested-by: Jean-Philippe Brucker <jean-philippe@...aro.org>
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>

Thanks for cleaning this up. Whether Vt-d's supervisor mode will need
rework or not, this is still good to have. One nit below if you resend

Reviewed-by: Jean-Philippe Brucker <jean-philippe@...aro.org>

[...]
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 32d448050bf7..fcc9d36b4b01 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -152,6 +152,19 @@ enum iommu_dev_features {
>  
>  #define IOMMU_PASID_INVALID	(-1U)
>  
> +/*
> + * The IOMMU_SVA_BIND_SUPERVISOR flag requests a PASID which can be used only
> + * for access to kernel addresses. No IOTLB flushes are automatically done
> + * for kernel mappings; it is valid only for access to the kernel's static
> + * 1:1 mapping of physical memory — not to vmalloc or even module mappings.
> + * A future API addition may permit the use of such ranges, by means of an
> + * explicit IOTLB flush call (akin to the DMA API's unmap method).
> + *
> + * It is unlikely that we will ever hook into flush_tlb_kernel_range() to
> + * do such IOTLB flushes automatically.

I would add that this is platform specific and not all IOMMU drivers
support the feature.

Thanks,
Jean

> + */
> +#define IOMMU_SVA_BIND_SUPERVISOR       BIT(0)
> +
>  #ifdef CONFIG_IOMMU_API