kexec failure with Xen 4.19-rc4 and 4.20-dev on linux host

[Jan Beulich]

On 05.08.2024 09:52, Juergen Gross wrote:
> On 05.08.24 08:01, Jan Beulich wrote:
>> On 04.08.2024 15:17, A Kundu wrote:
>>> On 8/2/24 13:25, Jan Beulich wrote:
>>>   > On 02.08.2024 09:28, A Kundu wrote:
>>>   >> On 8/2/24 09:06, Baoquan He wrote:
>>>   >>> On 07/31/24 at 06:34pm, A Kundu wrote:
>>>   >>>> I am experiencing issues using kexec to load Xen 4.17(debian's apt
>>> version),
>>>   >>>> Xen 4.19-rc4 (compiled from source) and 4.20-dev (compiled from
>>> source) on a
>>>   >>>> debian host.
>>>   >>> You should CC this to XEN dev list so that XEN dev knows this and may
>>>   >>> provide help. Not everyone is interested in and knows XEN.
>>>   >>>
>>>   >>>> System information:
>>>   >>>> $ uname -a
>>>   >>>> Linux host 6.9.10-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.9.10-1
>>> (2024-07-19)
>>>   >>>> x86_64 GNU/Linux
>>>   >>>>
>>>   >>>> $ kexec --version # compiled from source tarball with ./configure
>>> --with-xen
>>>   >>>> kexec-tools 2.0.29
>>>   >>>>
>>>   >>>> Steps to reproduce:
>>>   >>>>
>>>   >>>> 1. Set variables:
>>>   >>>>
>>>   >>>> XEN_HYPERVISOR="/boot/xen.gz"
>>>   >>>> XEN_CMD="dom0_mem=6G dom0_max_vcpus=6 dom0_vcpus_pin cpufreq=xen"
>>>   >>>>
>>>   >>>> 2. Attempt to load Xen 4.19-rc4:
>>>   >>>>
>>>   >>>> # kexec -l "$XEN_HYPERVISOR" --command-line="$XEN_CMD"
>>>   >>>> Could not find a free area of memory of 0x3b6001 bytes...
>>>   >>>> elf_exec_build_load_relocatable: ELF exec load failed
>>>   >>>>
>>>   >>>> 3. Attempt to load Xen 4.20-dev:
>>>   >>>>
>>>   >>>> # kexec -l "$XEN_HYPERVISOR" --command-line="$XEN_CMD"
>>>   >>>> Could not find a free area of memory of 0x3f8001 bytes...
>>>   >>>> elf_exec_build_load_relocatable: ELF exec load failed
>>>   >>>>
>>>   >>>> 4. Attempt to load Xen 4.17 (from debian rrepositories):
>>>   >>>> # kexec -l /boot/xen-4.17-amd64.gz --command-line="$XEN_CMD"
>>>   >>>> Could not find a free area of memory of 0x3b4001 bytes...
>>>   >>>> elf_exec_build_load_relocatable: ELF exec load failed
>>>   >
>>>   > And with all of them saying effectively the same, did you verify you
>>>   > actually have a sufficiently large area reserved? The obvious
>>>   > place for you to look at is Xen's boot log (obtained via serial
>>>   > console or "xl dmesg" immediately after booting the system). If you
>>>   > find everything as expected there, ...
>>>   >
>>>   >>>> If you need any further information to investigate this problem,
>>>   >>>> please let me know.
>>>   >
>>>   > ... please provide that boot log.
>>>
>>> I have also followed up on your suggestion to check the Xen boot log
>>> using "xl dmesg", but unfortunately, I received the following error:
>>>
>>> xencall: error: Could not obtain handle on privileged command interface:
>>> No such file or directory
>>> libxl: error: libxl.c:102:libxl_ctx_alloc: cannot open libxc handle: No
>>> such file or directory
>>> cannot init xl context
>>>
>>> This indicates that Xen did not boot successfully, so there are no logs
>>> available.
>>
>> The fact that you have Dom0 up makes clear that Xen booted okay(ish). The
>> fact that you get "No such file or directory" from xencall suggests you
>> either didn't load the xen-privcmd driver (normally arrangements are made
>> by distros for this to happen automatically), or you didn't even build it.
> 
> The messages seen don't indicate that Xen booted okay(ish). I get the same
> messages when having booted the Linux kernel on bare metal without Xen.

Hmm, I didn't even think of this as a possible case, considering the question
was forwarded to xen-devel (from a kexec list). I'm afraid Xen simply plays
no role when setting up kexec (to whatever target) from a bare metal env.

Jan