Re: [PATCH v2 0/3] arm-smmu: select suitable IOVA

[Shyam Saini]

Hi Jason,

apologies for the delayed response.

> On Wed, Apr 16, 2025 at 11:04:27AM -0700, Jacob Pan wrote:
> 
> > Per last discussion "SMMU driver have a list of potential addresses and
> > select the first one that does not intersect with the non-working IOVA
> > ranges.". If we don't know what the "non-working IOVA" is, how do we
> > know it does not intersect the "potential addresses"?
> 
> I had understood from previous discussions that this platform is
> properly creating IOMMU_RESV_RESERVED regions for the IOVA that
> doesn't work. Otherwise everything is broken..
> 
> Presumably that happens through iommu_dma_get_resv_regions() calling
> of_iommu_get_resv_regions() on a DT platform. There is a schema
> describing how to do this, so platform firmware should be able to do it..
> 
> So the fix seems trivial enough to me:
> 
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c 
> b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index b4c21aaed1266a..ebba18579151bc 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -3562,17 +3562,29 @@ static int arm_smmu_of_xlate(struct device *dev,
>  static void arm_smmu_get_resv_regions(struct device *dev,
>                                     struct list_head *head)
>  {
> -     struct iommu_resv_region *region;
> -     int prot = IOMMU_WRITE | IOMMU_NOEXEC | IOMMU_MMIO;
> -
> -     region = iommu_alloc_resv_region(MSI_IOVA_BASE, MSI_IOVA_LENGTH,
> -                                      prot, IOMMU_RESV_SW_MSI, GFP_KERNEL);
> -     if (!region)
> -             return;
> -
> -     list_add_tail(&region->list, head);
> +     static const u64 msi_bases[] = { MSI_IOVA_BASE, 0x12340000 };
>  
>       iommu_dma_get_resv_regions(dev, head);

my understand is, this hook is not called for all the devices, eg: pcie dts node
doesn't use [1] "iommus" property instead it uses "iommu-map" property
as a consequence, [1] while loop exits prematurely and 
iommu_dma_get_resv_regions()
is not called, so there is no IOVA reservation for the pcie device. 

Did i miss something? Please let me know.

[1] https://elixir.bootlin.com/linux/v6.15-rc7/source/drivers/of/device.c#L161

Thanks,
Shyam