Real mode kexec failure with non-IDE disk

David Woodhouse dwmw2 at
Sun Apr 28 14:05:33 PDT 2019

When I kexec either Xen or Linux in real mode, from either Xen or
Linux, it fails.

The last thing I see looks like SeaBIOS trying to use SMM for call32:

0x00000000000f70ec:  mov    %eax,%esi
0x00000000000f70ef:  mov    $0xb5,%eax
0x00000000000f70f5:  mov    $0x1234,%ecx
0x00000000000f70fb:  mov    $0xef3dc,%ebx
0x00000000000f7101:  out    %al,$0xb2
0x00000000000f7103:  pause  

0x00000000000ef3db:  hlt    

This happens when the real mode boot code calls INT 13h to read from
the disk. It seems to happen with virtio and SATA disks.

This is with the Ubuntu-packaged 1.10.2-1ubuntu1 SeaBIOS. Switching to
an IDE disk, or booting with 'edd=skipmbr', makes Xen work and Linux
get a little further before it dies anyway.
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