Re: [PATCH v5 untested] kvm: better MWAIT emulation for guests

Gabriel L. Somlo
2017-03-16T20:17:11Z

On Thu, Mar 16, 2017 at 09:27:56PM +0200, Michael S. Tsirkin wrote:
> On Thu, Mar 16, 2017 at 03:24:41PM -0400, Gabriel L. Somlo wrote:
> > On Thu, Mar 16, 2017 at 08:29:32PM +0200, Michael S. Tsirkin wrote:
> > > Let's take a step back and try to figure out how is
> > > mwait called. How about dumping code of VCPUs
> > > around mwait? gdb disa command will do this.
> >
> > Started guest with '-s', tried to attach from gdb with
> > "target remote localhost:1234", got
> > "remote 'g' packet reply is too long: <lengthy string of numbers>"
>
> Try
>
> set arch x86-64:x86-64

'set architecture i386:x86-64:intel' is what worked for me;

Been rooting around for a while, can't find mwait or monitor :(

Guess I'll have to recompile KVM to actually issue an invalid opcode,
so OS X will print a panic message with the exact address :)

Stay tuned...

>
> > Tried typing 'cont' in the qemu monitor, got os x to crash:
> >
> > panic (cpu 1 caller 0xffffff7f813ff488): pmLock: waited too long, held
> > by 0xffffff7f813eff65
> >
> > Hmm, maybe that's where it keeps its monitor/mwait idle loop.
> > Restarted the guest, tried this from monitor:
> >
> > dump-guest-memory foobar 0xffffff7f813e0000 0x20000
> >
> > Got "'dump-guest-memory' has failed: integer is for 32-bit values"
> >
> > Hmmm... I have no idea what I'm doing anymore at this point... :)
> >
> > --G
>
> I think 0xffffff7f813ff488 is a PC.
>
> --
> MST