Date:   Sat, 28 Jan 2023 16:49:11 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        Robin Murphy <robin.murphy@....com>
Cc:     baolu.lu@...ux.intel.com, joro@...tes.org, will@...nel.org,
        hch@....de, iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/8] iommu: Decouple iommu_present() from bus ops

On 2023/1/27 23:43, Jason Gunthorpe wrote:
> On Fri, Jan 27, 2023 at 03:19:55PM +0000, Robin Murphy wrote:
> 
>> The current implementation of device_iommu_mapped() just dates back to when
>> dev->iommu_group was the only per-device thing we had, so in principle I
>> don't have any conceptual objection to redefining it in terms of "device has
>> ops" rather than "device has a group", but as things stand you'd still have
>> to do something about PPC first (I know Jason had been pushing on that, but
>> I've not kept track of where it got to).
> PPC hasn't moved at all, AFAICT. In a few more months I'm going to
> suggest we delete the special VFIO support due to it being broken,
> distros already having turned it off and nobody caring enough to fix
> it..
> 
> What does device_iommu_mapped() even really mean?
> 
> Looking at usages..
> 
> These are fixing SOC HW bugs/issues - the desire seems to be "is the SOC's
> IOMMU enabled"
> 
> drivers/char/agp/intel-gtt.c:           device_iommu_mapped(&intel_private.pcidev->dev));
> drivers/dma/sh/rcar-dmac.c:     if (device_iommu_mapped(&pdev->dev))
> drivers/gpu/drm/i915/i915_utils.c:      if (device_iommu_mapped(i915->drm.dev))
> ?
> drivers/usb/dwc3/dwc3-xilinx.c: if (of_dma_is_coherent(dev->of_node) || device_iommu_mapped(dev)) {
> drivers/usb/host/xhci.c:        if (!(xhci->quirks & XHCI_ZERO_64B_REGS) || !device_iommu_mapped(dev))
> drivers/crypto/qat/qat_common/adf_sriov.c:      if (!device_iommu_mapped(&pdev->dev))
> ?
> 
> These seem to be trying to decide if iommu_domain's can be used (and
> they can't be on power):
> 
> drivers/gpu/drm/msm/msm_drv.c:  if (device_iommu_mapped(mdp_dev))
> drivers/gpu/drm/msm/msm_drv.c:          device_iommu_mapped(dev->dev) ||
> drivers/gpu/drm/msm/msm_drv.c:          device_iommu_mapped(dev->dev->parent);
> drivers/gpu/drm/nouveau/nvkm/engine/device/tegra.c:     if (device_iommu_mapped(dev)) {
> drivers/gpu/drm/rockchip/rockchip_drm_drv.c:    if (!device_iommu_mapped(dev))
> drivers/gpu/drm/tegra/uapi.c:   if (device_iommu_mapped(client->base.dev) && client->ops->can_use_memory_ctx) {
> drivers/gpu/host1x/context.c:           if (!fwspec || !device_iommu_mapped(&ctx->dev)) {
> drivers/infiniband/hw/usnic/usnic_ib_main.c:    if (!device_iommu_mapped(&pdev->dev)) {
> 
> Yikes, trying to map DMA addresses programmed into devices back to CPU addresses:
> 
> drivers/misc/habanalabs/common/debugfs.c: if (!user_address || device_iommu_mapped(&hdev->pdev->dev)) {
> drivers/misc/habanalabs/gaudi2/gaudi2.c:                if (!device_iommu_mapped(&hdev->pdev->dev))
> 
> And then sequencing the call to iommu_probe_device() which doesn't
> apply to power:
> 
> drivers/acpi/scan.c:    if (!err && dev->bus && !device_iommu_mapped(dev))
> drivers/iommu/of_iommu.c:       if (!err && dev->bus && !device_iommu_mapped(dev))
> 
> Leaving these:
> 
> arch/powerpc/kernel/eeh.c:      if (device_iommu_mapped(dev)) {
> 
> This is only used to support eeh_iommu_group_to_pe which is only
> caleld by vfio_iommu_spapr_tce.c. Since power vfio doesn't work right
> now this is uncallable, and when power is fixed this will work
> properly.
> 
> arch/powerpc/kernel/iommu.c:    if (device_iommu_mapped(dev)) {
> arch/powerpc/kernel/iommu.c:    if (!device_iommu_mapped(dev)) {
> 
> These should both be replaced with some kind of 'device has iommu group', since
> it is really driving ppc unique group logic.
> 
> So, I'd say Baolu's approach is the right thing, just replace the
> above two in ppc with something else.

Thank you both. I will follow up a series later.

Best regards,
baolu

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