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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Sun, Aug 18, 2019 at 10:00:17PM -0700, Roman Shaposhnik wrote:
> Hi Roger!
> 
> Some good news, some bad news ;-)
> 
> Good news is that on the newer BIOS, your original patch seems to work fine.
> 
> IOW, with newer BIOS:
>     1. without your original patch I see garbled screen
>     2. with your original patch everything boots normally.

That would be my expectation.

> Bad news is that with older BIOS, your original patch seems to either
> work or not depending on the BIOS some of the BIOS settings.
> 
> IOW, with older BIOS:
>     1. without your original patch I see garbled screen (regardless of
> BIOS settings)
>     2. with your original patch AND resetting to a factory defaults of
> BIOS settings -- everything boots normally
>     3. when I load up our custom settings -- the only thing that can
> boot normally is the latest patch
> 
> So, would it make sense and commit your original patch for now? This
> will unlock me with newer BIOSes on these boxes.

I think so, can you please provide a tested-by to the patch:

https://lists.xenproject.org/archives/html/xen-devel/2019-07/msg01547.html

Feel free to also note the weird behaviour you are seeing with this
box and firmware version.

> As for the older BIOSes, I still feel that it would be great for Xen
> to boot more reliably -- especially since Xen 4.10 seems to be doing
> fine regardless of BIOS version and settings.
> 
> What do you think?

We could add a quirk for this fimrware version and hardware if we know
exactly what the issue is. Have you figured out if it's related to the
flush? ie: iommu_iotlb_flush vs iommu_iotlb_flush_all vs iommu_flush_all?

Thanks, Roger.

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