UML not coming up on "INTEL(R) XEON(R) GOLD 6542Y"

[Benjamin Berg]

Hi,

On Tue, 2024-09-17 at 10:08 +0200, Benjamin Berg wrote:
> if it is really only on that CPU, then maybe it is related to AMX
> support? Though, not sure how exactly that might be affecting
> PTRACE_{S,G}ETFPREGS on x86_64.

Just, FYI, it really cannot work if the host kernel has AMX enabled.
The reason is that PTRACE_SETREGSET on NT_X86_XSAVE expects that the
passed buffer has the maximum theoretical size (I suppose even if the
feature isn't even enabled for the process).

Seems like the only way to make this work is to discover the xstate
size from the host kernel. I guess by passing a very large buffer to
PTRACE_GETREGSET and checking the iovec for the filled in length.

I think you can work around it by setting
  clearcpuid=amx_tile
on the host kernel command line.

Benjamin


> On Mon, 2024-09-16 at 13:09 +0000, Vijay Tandeker wrote:
> > 
> > 
> > Hi, thanks to all for helping me in the past. I need one more help.
> > Getting the below error on running UML:
> > -------------------------------------------------------------------
> > --
> > -------------------------
> > Run /sbin/init as init process
> > userspace - ptrace set fp regs failed, errno = 14
> > Kernel panic - not syncing: Attempted to kill init!
> > exitcode=0x0000000b
> > CPU: 0 PID: 1 Comm: init Not tainted 6.8.9-1 #1
> > -------------------------------------------------------------------
> > --
> > -------------------------
> > 
> > Searched on the internet but didn't find any solution. Any idea,
> > what
> > could be the reason for the above error? Below are my UML details:
> > 1) root-fs: created by running the command: “debootstrap --
> > arch=amd64
> > noble /tmp http://archive.ubuntu.com/ubuntu/”
> > 2) Linux: created by running the command: "ARCH=um make -j$(nproc)"
> > on linux-6.8.9 using defconfig.
> > 3) Attached file <uml_crash>: logs on running the UML
> > 4) Attached file <system_info>: my host system details
> > 5) INTEL(R) XEON(R) GOLD 6542Y
> > 6) RAM: 256 GB
> > 7) Ubuntu 24.04.1 LTS
> > 
> > Please let me know if you need more information.
> > 
> 
> 
>