Re: [libvirt] [Qemu-devel] [PATCH v4] vl.c deprecate incorrect CPUs topology

-smp [cpus],sockets/cores/threads[,maxcpus] should describe topology so that total number of logical CPUs [sockets * cores * threads] would be equal to [maxcpus], however historically we didn't have such check in QEMU and it is possible to start VM with an invalid topology. Deprecate invalid options combination so we can make sure that the topology VM started with is always correct in the future. Users with an invalid sockets/cores/threads/maxcpus values should fix their CLI to make sure that [sockets * cores * threads] == [maxcpus] Signed-off-by: Igor Mammedov <imammedo(a)redhat.com&gt; --- v4: - missed dot comment, fix it with s/./,/ (Andrew Jones <drjones(a)redhat.com>) v3: - more spelling fixes (Andrew Jones <drjones(a)redhat.com>) - place deprecation check after (sockets * cores * threads > max_cpus) check (Eduardo Habkost <ehabkost(a)redhat.com>) v2: - spelling&&co fixes (Andrew Jones <drjones(a)redhat.com>) --- qemu-deprecated.texi | 11 +++++++++++ vl.c | 7 +++++++ 2 files changed, 18 insertions(+) diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi index 87212b6..094b4ca 100644 --- a/qemu-deprecated.texi +++ b/qemu-deprecated.texi @@ -159,6 +159,17 @@ The 'file' driver for drives is no longer appropriate for character or host devices and will only accept regular files (S_IFREG). The correct driver for these file types is 'host_cdrom' or 'host_device' as appropriate. +@subsection -smp X,[socket=a,core=b,thread=c],maxcpus=Y (since 3.1) + +CPU topology properties should describe whole machine topology including +possible CPUs, but historically it was possible to start QEMU with +an incorrect topology where + sockets * cores * threads >= X && X < maxcpus +which could lead to an incorrect topology enumeration by the guest. +Support for invalid topologies will be removed, the user must ensure +topologies described with -smp include all possible cpus, i.e. + sockets * cores * threads == maxcpus + @section QEMU Machine Protocol (QMP) commands @subsection block-dirty-bitmap-add "autoload" parameter (since 2.12.0) diff --git a/vl.c b/vl.c index 5ba06ad..7fd700e 100644 --- a/vl.c +++ b/vl.c @@ -1246,6 +1246,13 @@ static void smp_parse(QemuOpts *opts) exit(1); } + if (sockets * cores * threads != max_cpus) { + warn_report("Invalid CPU topology deprecated: " + "sockets (%u) * cores (%u) * threads (%u) " + "!= maxcpus (%u)", + sockets, cores, threads, max_cpus); + } + smp_cpus = cpus; smp_cores = cores; smp_threads = threads; -- 2.7.4