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Re: [Xen-devel] [BUG] After upgrade to Xen 4.12.0 iommu=no-igfx
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <JBeulich@xxxxxxxx>
- Date: Thu, 1 Aug 2019 07:35:42 +0000
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- Cc: Juergen Gross <JGross@xxxxxxxx>, Roman Shaposhnik <roman@xxxxxxxxxx>, Paul Durrant <Paul.Durrant@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, "boris.ostrovsky@xxxxxxxxxx" <boris.ostrovsky@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Thu, 01 Aug 2019 07:39:18 +0000
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- Thread-topic: [Xen-devel] [BUG] After upgrade to Xen 4.12.0 iommu=no-igfx
On 31.07.2019 21:46, Andrew Cooper wrote:
> My bet is on the intel_iommu_lookup_page() call having side effects[1].
> If you take out the debugging in the middle of the loop in
> rmrr_identity_mapping(), does the problem reproduce again?
While your guess was right according to Roman's latest results, I'd
still like to note that ...
> [1] Looking at the internals of addr_to_dma_page_maddr(), it does 100%
> more memory allocation and higher-level PTE construction than looks wise
> for what is supposed to be a getter.
... there being 0 passed as last argument is supposed to suppress
any allocations (and from looking at the function I can't really
see any side effects yet in this case; all I do see is that the
first check of "alloc" could/should happen before looking up
PCI device and DRHD).
I've also double checked - there clearly is a flush after the call
to setup_hwdom_rmrr(). I'm not even convinced this flush has much
value, seeing that translation gets enabled only afterwards.
Jan
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