Re: [Xen-devel] [Xen EFI] Impossible to limit the dom0 memory

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 25.01.18 at 11:25, <msd+xen-devel@xxxxxx> wrote:
>>  Xen doesn't crash at all.

Did you read the above? it is being confirmed by ...

> With this file, it works, Xen boots :
> 
> ```
> [global]
> default=xen
> 
> [xen]
> options=loglvl=all com1=115200,8n1 console=com1,vga
> kernel=vmlinuz root=/dev/md2 ro rootdelay=10 noquiet nosplash 
> earlyprintk=xen
> ramdisk=initrd.img
> ```
> 
> With this file, I have just added "dom0_mem=1G,max:1G", Xen crashes :
> 
> ```
> [global]
> default=xen
> 
> [xen]
> options=loglvl=all com1=115200,8n1 console=com1,vga dom0_mem=1G,max:1G
> kernel=vmlinuz root=/dev/md2 ro rootdelay=10 noquiet nosplash 
> earlyprintk=xen
> ramdisk=initrd.img
> ```
> 
> I attached the boot logs "dom0_crash_with_dom0_memory.txt". The last 
> line is "(XEN) Hardware Dom0 crashed: rebooting machine in 5 seconds."

... this line you observe. Taking further lines from the log you've
provided subsequently:

(XEN) d0v0: unhandled page fault (ec=0003)                                      
                                                                                
                              

This tells us that Dom0 didn't install a page fault handler yet.

(XEN) Pagetable walk from ffffffff82565200:                                     
                                                                                
                              
(XEN)  L4[0x1ff] = 000000084600e067 000000000000200e                            
                                                                                
                              
(XEN)  L3[0x1fe] = 000000084600f067 000000000000200f                            
                                                                                
                              
(XEN)  L2[0x012] = 0000000846647067 0000000000002647                            
                                                                                
                              
(XEN)  L1[0x165] = 0010000846565065 0000000000002565                            
                                                                                
                              

This tells us (together with the page fault error code) that the
Dom0 kernel tried to provide memory as kernel stack which
can't be written. This may be a Dom0 kernel stack overflow,
but there may also be other reasons. At this point I can't
exclude there being some root cause in Xen, but the issue
needs to be investigated from the Dom0 kernel side.

Jan


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