Re: [Xen-devel] [PATCH for-4.12] passthrough/vtd: Drop the "workaround_bios_bug" logic entirely

[Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>]

On 21/03/2019 20:26, Andrew Cooper wrote:
> It turns out that this code was previously dead.
> 
> c/s dcf41790 " x86/mmcfg/drhd: Move acpi_mmcfg_init() call before calling
> acpi_parse_dmar()" resulted in PCI segment 0 now having been initialised
> enough for acpi_parse_one_drhd() to not take the
> 
>   /* Skip checking if segment is not accessible yet. */
> 
> path unconditionally.  However, some systems have DMAR tables which list
> devices which are disabled by user choice (in particular, Dell PowerEdge R740
> with I/O AT DMA disabled), and turning off all IOMMU functionality in this
> case is entirely unhelpful behaviour.
> 
> Leave the warning which identifies the problematic devices, but drop the
> remaining logic.  This leaves the system in better overall state, and working
> in the same way that it did in previous releases.
> 
> Reported-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>

Igor

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