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

Jean-Philippe Brucker
2021-05-12T10:18:35Z

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@linaro.org>
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.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@linaro.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