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Re: [Xen-devel] [BUG] After upgrade to Xen 4.12.0 iommu=no-igfx

On 06.08.2019 23:48, Roman Shaposhnik wrote:
On Tue, Aug 6, 2019 at 9:18 AM Roger Pau Monné <roger.pau@xxxxxxxxxx> wrote:

On Fri, Aug 02, 2019 at 10:05:40AM +0200, Roger Pau Monné wrote:
On Thu, Aug 01, 2019 at 11:25:04AM -0700, Roman Shaposhnik wrote:
This patch completely fixes the problem for me!

Thanks Roger! I'd love to see this in Xen 4.13

Thanks for testing!

It's still not clear to me why the previous approach didn't work, but
I think this patch is better because it removes the usage of
{set/clear}_identity_p2m_entry from PV domains. I will submit this
formally now.

Sorry to bother again, but since we still don't understand why the
previous fix didn't work for you, and I can't reproduce this with my
hardware, could you give the attached patch a try?

No worries -- and thanks for helping to get it over the finish line --
this is much appreciated!

I'm happy to say that this latest patch is also working just fine. So
I guess this is the one that's going to land in Xen 4.13?

Not necessarily - the other patch is also a candidate, but its
description would need to explain what was actually wrong.

AFAICT the only difference between the non-working version and the
working version is the flush, so I've added it here.

Now I'm afraid I still can't draw a helpful conclusion from Roman's
successful test: intel_iommu_hwdom_init(), after having called
setup_hwdom_rmrr(), calls iommu_flush_all() (with one other,
seemingly innocent call in between). The only conclusion I _could_
draw is that iommu_flush_all() doesn't do what its name says. Which
would be quite bad. But

-> iommu_flush_iotlb_global(flush_non_present_entry=0)
-> flush->iotlb(DMA_TLB_GLOBAL_FLUSH, flush_non_present_entry=0)

-> iommu_flush_iotlb(dma_old_pte_present=0, page_count=0)
-> iommu_flush_iotlb_dsi(flush_non_present_entry=0)
-> flush->iotlb(DMA_TLB_DSI_FLUSH, flush_non_present_entry=0)

suggests to me that (as one would infer from the names) is the
more through flush. I must be overlooking something ...


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