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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] bad page flags booting 32bit dom0 on 64bit hypervisor using dom0_mem (kernel >=4.2)
On 02.05.2016 13:41, Juergen Gross wrote: > On 02/05/16 12:47, Stefan Bader wrote: >> I recently tried to boot 32bit dom0 on 64bit Xen host which I configured to >> run >> with a limited, fix amount of memory for dom0. It seems that somewhere >> between >> kernel versions 3.19 and 4.2 (sorry that is still a wide range) the Linux >> kernel >> would report bad page flags for a range of pages (which seem to be around the >> end of the guest pfn range). For a 4.2 kernel that was easily missed as the >> boot >> finished ok and dom0 was accessible. However starting with 4.4 (tested 4.5 >> and a >> 4.6-rc) the serial console output freezes after some of those bad page flag >> messages and then (unfortunately without any further helpful output) the host >> reboots (I assume there is a panic that triggers a reset). >> >> I suspect the problem is more a kernel side one. It is just possible to >> influence things by variation of dom0_mem=#,max:#. 512M seems ok, 1024M, >> 2048M, >> and 3072M cause bad page flags starting around kernel 4.2 and reboots around >> 4.4. Then 4096M and not clamping dom0 memory seem to be ok again (though not >> limiting dom0 memory seems to cause trouble on 32bit dom0 later when a domU >> tries to balloon memory, but I think that is a different problem). >> >> I have not seen this on a 64bit dom0. Below is an example of those bad page >> errors. Somehow it looks to be a page marked as reserved. Initially I >> wondered >> whether this could be a problem of not clearing page flags when moving >> mappings >> to match the e820. But I never looked into i386 memory setup in that detail. >> So >> I am posting this, hoping that someone may have an idea from the detail about >> where to look next. PAE is enabled there. Usually its bpf init that gets hit >> but >> that likely is just because that is doing the first vmallocs. > > Could you please post the kernel config, Xen and dom0 boot parameters? > I'm quite sure this is no common problem as there are standard tests > running for each kernel version including 32 bit dom0 with limited > memory size. Hi Jürgen, sure. Though by doing that I realized where I actually messed the whole thing up. I got the max limit syntax completely wrong. :( Instead of the correct "dom0_mem=1024M,max:1024M" I am using "dom0_mem=1024M:max=1024M" which I guess is like not having max set at all. Not sure whether that is a valid use case. When I actually do the dom0_mem argument right, there are no bad page flag errors even in 4.4 with 1024M limit. I was at least consistent in my mis-configuration, so doing the same stupid thing on 64bit seems to be handled more gracefully. Likely false alarm. But at least cut&pasting the config into mail made me spot the problem... -Stefan The xen boot parameters: dom0_mem=1024M:max=1024M loglvl=all guest_loglvl=all hvm_debug=0 com1=57600,8n1 console=com1,vga The dom0 boot parameters: nomodeset loglevel=10 earlyprintk=xenboot console=tty0 console=hvc0 The config is attached (for size reasons). I picked the 4.2 config as that kernel only has the errors but allows me to boot into something that appears to be working ok. -Stefan > > > Juergen > Attachment:
config-4.2.0-35-generic Attachment:
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