Re: [Xen-devel] [PATCH] VT-d/DMAR: accept DRHD with non-discoverable PCI devices

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Wed, Mar 20, 2019 at 08:22:03PM +0000, Igor Druzhinin wrote:
> Since commit dcf41790 ("x86/mmcfg/drhd: Move acpi_mmcfg_init() call
> before calling acpi_parse_dmar()") PCI segment 0 is now known early
> which made the sanity check on DRHD definition structure to work.
> This, in turn, caused a regression on some machines (in particular,
> HP PowerEdge R740 with I/O AT DMA disabled) where IOMMU was explicitly
^^^^

That's probably a typo.. sounds like it should say "Dell PowerEdge R740", not 
HP.. 


-- Pasi

> disabled due to some internal PCI devices being non-discoverable but
> present in DMAR.
> 
> While this is indeed a BIOS mistake it seems to be not that critical
> to disable the whole IOMMU. Instead, extend the scope of
> "workaround_bios_bug" option and make it enabled by default. This is
> consistent with our documentation and actually what a user might expect
> from an option with that name. It also doesn't seem safe to simply ignore
> DRHD without initialization so remove this case. But leave the original
> DMAR check in place to still allow error reporting.
> 
> Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>

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