Re: [BUG] x2apic broken with current AMD hardware

[Elliott Mitchell <ehem+xen@xxxxxxx>]

On Thu, Mar 09, 2023 at 10:03:23AM +0100, Jan Beulich wrote:
> On 09.03.2023 00:08, Elliott Mitchell wrote:
> > 
> > As such I'm less than certain the problem is still in HEAD, though
> > Neowutran and Co working with 4.16 and the commit log being quiet
> > suggests there is a good chance.
> > 
> > More detail, pretty well most things are broken for Domain 0 without
> > "x2apic=false".  Trying to boot with a 6.1.12 a USB keyboard was
> > completely unresponsive, on screen the initial ramdisk script output was
> > indicating problems interacting with storage devices.  Those two together
> > suggested an interrupt issue and adding "x2apic=false" caused domain 0 to
> > successfully boot.
> > A 5.10 kernel similarly requires "x2apic=false" to successfully boot.
> > 
> > So could be a commit after 4.16 fixed x2apic for current AMD hardware,
> > but may still be broken.
> 
> If Dom0 boot is affected, trying a newer hypervisor shouldn't be a problem.
> You won't need any of the toolstack to match just to see whether Dom0 boots.
> 
> In any event you will want to collect a serial log at maximum verbosity.
> It would also be of interest to know whether turning off the IOMMU avoids
> the issue as well (on the assumption that your system has less than 255
> CPUs).

Well, I can now state "x2apic=false" IS required for Xen 4.17.  Since the
last x2apic commit was about a year ago, I believe this matches HEAD.  I
missed the logs since the USB-serial adapter decided to bugger when the
machine rebooted.

Is it just me or is https://wiki.xenproject.org/wiki/Xen_Serial_Console
out of date?

Last time I used serial debugging I recall the options being different.
Due to stress level this time I'm not so favorable to looking things up
in Git (this system is crucial in my development workflow, so being in a
problematic state is trouble).


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