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

[Thomas Huth]

On 18.07.2016 11:26, Greg Kurz wrote:
> 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

FWIW, with that command line, I still don't get an assertion but a
normal error message:

qemu-system-ppc64: -device pc-dimm,id=dimm-mem1,memdev=mem-mem1: can't
use already busy memdev: mem-mem1

 Thomas

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