Daniel P. Berrangé wrote:
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=343642&view=markup#l520
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"/>
Sounds good to me, I'll send v2 soon.
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 :|
Roman Bogorodskiy