Re: [Qemu-devel] [Qemu-ppc] [PATCH] ppc: Yet another fix for the huge page support detection mechanism

[Greg Kurz]

On Mon, 18 Jul 2016 11:04:39 +0200
Thomas Huth <address@hidden> wrote:

> On 18.07.2016 10:59, Greg Kurz wrote:
> > On Mon, 18 Jul 2016 10:52:36 +1000
> > David Gibson <address@hidden> wrote:
> >   
> >> On Fri, Jul 15, 2016 at 10:10:25AM +0200, Thomas Huth wrote:  
> >>> Commit 86b50f2e1bef ("Disable huge page support if it is not available
> >>> for main RAM") already made sure that huge page support is not announced
> >>> to the guest if the normal RAM of non-NUMA configurations is not backed
> >>> by a huge page filesystem. However, there is one more case that can go
> >>> wrong: NUMA is enabled, but the RAM of the NUMA nodes are not configured
> >>> with huge page support (and only the memory of a DIMM is configured with
> >>> it). When QEMU is started with the following command line for example,
> >>> the Linux guest currently crashes because it is trying to use huge pages
> >>> on a memory region that does not support huge pages:
> >>>
> >>>  qemu-system-ppc64 -enable-kvm ... -m 1G,slots=4,maxmem=32G -object \
> >>>    
> >>> memory-backend-file,policy=default,mem-path=/hugepages,size=1G,id=mem-mem1
> >>>  \
> >>>    -device pc-dimm,id=dimm-mem1,memdev=mem-mem1 -smp 2 \
> >>>    -numa node,nodeid=0 -numa node,nodeid=1
> >>>
> >>> To fix this issue, we've got to make sure to disable huge page support,
> >>> too, when there is a NUMA node that is not using a memory backend with
> >>> huge page support.
> >>>
> >>> Fixes: 86b50f2e1befc33407bdfeb6f45f7b0d2439a740
> >>> Signed-off-by: Thomas Huth <address@hidden>
> >>> ---
> >>>  target-ppc/kvm.c | 10 +++++++---
> >>>  1 file changed, 7 insertions(+), 3 deletions(-)    
> >>
> >> Applied to ppc-for-2.7, thanks.
> >>  
> > 
> > It looks like my replies to this patch were ignored... no big deal though 
> > :)  
> 
> I'll try to come up with an additional patch that fixes the remaining
> problem that you've found... Meanwhile, did you find out why you get
> that assertion that I was not able to recreate? Could you maybe post the
> exact command line to trigger that assertion?
> 

I hit the assertion when I specify pc-dimm devices on the command line:

qemu-system-ppc64 -enable-kvm ... -m 2G,slots=4,maxmem=32G \
 -object 
memory-backend-file,policy=default,mem-path=/mnt/kvm_hugepage,size=1G,id=mem-mem1
 \
 -device pc-dimm,id=dimm-mem1,memdev=mem-mem1 \
 -object memory-backend-file,policy=default,mem-path=/mnt,size=1G,id=mem-mem2 \
 -device pc-dimm,id=dimm-mem2,memdev=mem-mem2 \
 -smp 2 -numa node,nodeid=0,memdev=mem-mem1 \
 -numa node,nodeid=1,memdev=mem-mem2

>  Thomas
> 
>

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