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Re: [Qemu-devel] [PATCH RFC 0/4] fixes for pci tree


From: Hu Tao
Subject: Re: [Qemu-devel] [PATCH RFC 0/4] fixes for pci tree
Date: Mon, 16 Jun 2014 14:29:08 +0800
User-agent: Mutt/1.5.21 (2010-09-15)

On Sun, Jun 15, 2014 at 01:00:56PM +0300, Michael S. Tsirkin wrote:
> On Sat, Jun 14, 2014 at 12:48:55PM +0800, Hu Tao wrote:
> > Michael,
> > 
> > This is fixes for your pci tree.
> > 
> > patch 1 remove signed range as requested.
> 
> This also fixes make check failures so I applied this.
> 
> Others don't look like regressions to me -
> this is error handling in new functionality, correct?

Yes.


BTW, thre are two more problems:

1. if numa node number doesn't start from 0 then qemu will core dump.

cmd line:

./x86_64-softmmu/qemu-system-x86_64 -hda
/home/data/libvirt-images/f18.img  -m 128M,maxmem=2G,slots=3 -qmp
unix:/tmp/m,server,nowait -monitor stdio -enable-kvm -object
memory-backend-ram,id=m1,size=128M -numa node,nodeid=1,cpus=1,memdev=m1

This problem can be fixed by:

diff --git a/numa.c b/numa.c
index ce9382d..b00c5cf 100644
--- a/numa.c
+++ b/numa.c
@@ -270,10 +270,13 @@ void memory_region_allocate_system_memory(MemoryRegion 
*mr, Obj
     }
 
     memory_region_init(mr, owner, name, ram_size);
-    for (i = 0; i < nb_numa_nodes; i++) {
+    for (i = 0; i < MAX_NODES; i++) {
         Error *local_err = NULL;
         uint64_t size = numa_info[i].node_mem;
         HostMemoryBackend *backend = numa_info[i].node_memdev;
+        if (!backend) {
+            continue;
+        }
         MemoryRegion *seg = host_memory_backend_get_memory(backend, 
&local_err);
         if (local_err) {
             qerror_report_err(local_err);

2. your current pci tree doesn't compile because patch 'qmp: add query-memdev' 
is dropped
while commit 5b517e74ed7825(hmp: add info memdev) depends on it. 

but patch 'qmp: add query-memdev' itself has a problem: if memory-backend-ram 
is on the command
line but no numa, info memdev returns nothing:

./x86_64-softmmu/qemu-system-x86_64 -hda /home/data/libvirt-images/f18.img  -m 
128M,maxmem=2G,slots=3 -qmp unix:/tmp/m,server,nowait -monitor stdio 
-enable-kvm -object memory-backend-ram,id=m1,size=128M 
QEMU 2.0.50 monitor - type 'help' for more information
(qemu) info memdev
(nothing returned)

even worse, if with -numa mem=size then qemu will core dump:

./x86_64-softmmu/qemu-system-x86_64 -hda /home/data/libvirt-images/f18.img  -m 
128M,maxmem=2G,slots=3 -qmp unix:/tmp/m,server,nowait -monitor stdio 
-enable-kvm -object memory-backend-ram,id=m1,size=128M -numa 
node,nodeid=0,cpus=0,mem=128M
(qemu) info memdev
Segmentation fault (core dumped)

this is because query_memdev searchs for memdev information in 
numa_info[].node_memdev,
which don't have value if there is no numa or numa isn't used with 
memory-backend-ram.

the solution can be gather memdevs in a list. Or query at /objects?

> Thus I'll wait for comments on these to be resolved,
> and hopefully for some acks.
> 
> > There are 3 problems in current pci tree, as follows:
> > 
> > 1. pc-dimm specified on command line but only -m size (aka not -m 
> > size,maxmem,slots)
> > 
> > ./x86_64-softmmu/qemu-system-x86_64 -hda
> > /home/data/libvirt-images/f18.img -smp 2 -object
> > memory-backend-ram,size=512M,id=ram-node0,prealloc=y,policy=bind,host-nodes=0
> > -device pc-dimm,id=d0,memdev=ram-node0  -m 640M  -qmp
> > unix:/tmp/m,server,nowait -monitor stdio -enable-kvm
> > 
> > result:
> > 
> > qemu/hw/mem/pc-dimm.c:110: pc_dimm_get_free_addr: Assertion
> > `address_space_end > address_space_size' failed.
> > Aborted (core dumped)
> > 
> > patch 2 fixes this.
> > 
> > 2. using qemu monitor command object-add to add a memory-backend-ram
> >    object whose's size is too big
> > 
> > ./x86_64-softmmu/qemu-system-x86_64 -hda
> > /home/data/libvirt-images/f18.img -smp 2 -m 512M  -qmp
> > unix:/tmp/m,server,nowait -monitor stdio -enable-kvm
> > 
> > in monitor:
> > (qemu)object_add memory-backend-ram,size=40960G,id=mem0
> > 
> > result:
> > 
> > qemu just exits with message: Cannot set up guest memory 'mem0': Cannot 
> > allocate memory
> > 
> > patch 3 fixes this.
> > 
> > 3. specifying a non-existing directory for memory-backend-file
> > 
> > ./x86_64-softmmu/qemu-system-x86_64 -hda
> > /home/data/libvirt-images/f18.img -smp 2 -m 512M,maxmem=1000G,slots=100
> > -qmp unix:/tmp/m,server,nowait -monitor stdio -enable-kvm -object
> > memory-backend-file,size=512M,id=mem0,mem-path=/nonexistingdir -device
> > pc-dimm,id=d0,memdev=mem0
> > 
> > result:
> > 
> > /nonexistingdir: No such file or directory
> > Bad ram offset fffffffffffff000
> > Aborted (core dumped)
> >  
> > patch 4 fixes this.
> > 
> > 
> > please review. Thanks!
> > 
> > 
> > Hu Tao (4):
> >   get rid of signed range
> >   check if we have space left for hotplugged memory
> >   exec: don't exit unconditionally if failed to allocate memory
> >   memory-backend-file: error out if failed to allocate memory
> > 
> >  backends/hostmem-file.c            |   3 +
> >  backends/hostmem-ram.c             |   3 +
> >  exec.c                             |   6 +-
> >  hw/mem/pc-dimm.c                   |   7 +-
> >  include/qemu/range.h               | 144 
> > ++++++++++++-------------------------
> >  qapi/string-input-visitor.c        | 116 +++++++++++++++++-------------
> >  qapi/string-output-visitor.c       |  97 +++++++++++++------------
> >  tests/test-string-input-visitor.c  |   4 +-
> >  tests/test-string-output-visitor.c |   8 +--
> >  9 files changed, 182 insertions(+), 206 deletions(-)
> > 
> > -- 
> > 1.9.3



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