Messages in this thread | | | Date | Tue, 12 Dec 2023 14:20:56 +0800 | Subject | Re: [PATCH v2 4/6] iommu/vt-d: Remove 1:1 mappings from identity domain | From | Baolu Lu <> |
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On 12/11/23 11:58 AM, Tian, Kevin wrote: >>> there are two cases above which mandates IDENTITY. Have you confirmed >>> that those platforms support hardware passthrough? otherwise this >> change >>> is broken. >> Those two cases should be hardware quirks for SoC-integrated devices. It >> makes no reason that a quirk requires IOMMU passthrough translation, but >> the hardware doesn't support it. >> >> If, unfortunately, those quirks turn out to be workarounds for a poorly >> designed device driver, we should remove those quirks and request the >> device driver to utilize the DMA ownership framework to achieve the same >> functionality within the driver itself. >> > if that is the case you should fix the drivers first before breaking them. > > But at a glance looks those two quirks are just fine. > > For Azalia sound device the problem is that BIOS enables a dedicated > DMAR for it but allocates zero TLB entries to cause deadlock. This > implies a hw passthrough mode otherwise it's still broken.
Yes. It's safe for Azalia sound device.
> > For GFX it's a workaround added since day one. there is even still > an option CONFIG_INTEL_IOMMU_BROKEN_GFX_WA available. But > now its meaning is really disabling IOMMU instead of using identity. > > sounds like IDENTMAP_GFX can be fully removed now: > > #ifdef CONFIG_INTEL_IOMMU_BROKEN_GFX_WA > dmar_map_gfx = 0; > #endif
We should already remove the workaround for the 2.6 kernel. :-)
It's default "n". Therefore, if any gfx driver still needs this workaround, there should already be a bug report.
> > if (!dmar_map_gfx) > iommu_identity_mapping |= IDENTMAP_GFX;
So with above cleaned up, we have no need to worry about drivers that are not capable of handling remapped dma address any more.
Did I miss anything?
Best regards, baolu
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