Re: [libvirt] [PATCH 0/3] bhyve: implement MSRs ignore unknown writes feature

On Thu, Feb 07, 2019 at 06:05:25PM +0400, Roman Bogorodskiy wrote: > Daniel P. Berrangé wrote: > > > On Wed, Feb 06, 2019 at 04:00:06PM -0500, Cole Robinson wrote: > > > On 1/25/19 12:54 PM, Roman Bogorodskiy wrote: > > > > > > > > Roman Bogorodskiy (3): > > > > conf: introduce 'msrs' feature > > > > bhyve: implement MSRs ignore unknown writes feature > > > > news: document bhyve msrs feature > > > > > > > > docs/drvbhyve.html.in | 16 +++++++++ > > > > docs/formatdomain.html.in | 1 + > > > > docs/news.xml | 11 ++++++ > > > > docs/schemas/domaincommon.rng | 14 ++++++++ > > > > src/bhyve/bhyve_command.c | 4 +++ > > > > src/conf/domain_conf.c | 33 +++++++++++++++++ > > > > src/conf/domain_conf.h | 8 +++++ > > > > src/qemu/qemu_domain.c | 1 + > > > > .../bhyvexml2argvdata/bhyvexml2argv-msrs.args | 10 ++++++ > > > > .../bhyvexml2argv-msrs.ldargs | 3 ++ > > > > .../bhyvexml2argvdata/bhyvexml2argv-msrs.xml | 26 ++++++++++++++ > > > > tests/bhyvexml2argvtest.c | 1 + > > > > .../bhyvexml2xmlout-msrs.xml | 36 +++++++++++++++++++ > > > > tests/bhyvexml2xmltest.c | 1 + > > > > 14 files changed, 165 insertions(+) > > > > create mode 100644 tests/bhyvexml2argvdata/bhyvexml2argv-msrs.args > > > > create mode 100644 tests/bhyvexml2argvdata/bhyvexml2argv-msrs.ldargs > > > > create mode 100644 tests/bhyvexml2argvdata/bhyvexml2argv-msrs.xml > > > > create mode 100644 tests/bhyvexml2xmloutdata/bhyvexml2xmlout-msrs.xml > > > > > > > > > > The code looks fine to me but this needs a bit more context. > > > Particularly 'ignore' is a bit ambiguous here so I had to dig > > > > > > kvm+linux has arguably always ignored unknown MSRs but historically it > > > would print an error in host dmesg which often confused users quite a > > > bit. In the bhyve case it seems that unknown MSRs cause the VM to > > > essentially crash which is a pretty intense reaction. This option > > > disables that crashing behavior. So for this feature to be really > > > descriptive it would be <msrs crashOnUnknown='yes|no' /> or something > > > like that > > > > That is not actually the case for KVM. When KVM sees an unhandled > > MSR it will inject a GPF to the guest, which will usually cause the > > guest to crash. KVM does this GPF injection for both reads and writes > > of unknown MSRs. > > > > There is an opt-in kvm.ko option "ignore-msrs" which tells KVM > > to silently ignore unknown MSRs instead. Ideally the KVM option > > would be exposed to QEMU as an option, since when people do need > > it, they usually only need it for a single guest. > > > > > The bhyve man page says: > > > > > > https://www.freebsd.org/cgi/man.cgi?query=bhyve&sektion=8 > > > > > > -w Ignore accesses to unimplemented Model Specific Registers > > > (MSRs). This is intended for debug purposes. > > > > I'm curious whether this applies to boths reads & writes of unknown > > MSRs, or just to writes. '-w' naming suggests the latter, but the > > descrption "accesses" would suggest reads too. > > From what I can see by briefly looking at the code, it applies to both > reads and writes: > > https://svnweb.freebsd.org/base/head/usr.sbin/bhyve/bhyverun.c?revision=3... > > Check two functions below this line. Yes, I agree. This is good as its the same behaviour as KVM. How about we change the XML to <msrs unknown="ignore|fault"/>

Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|