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

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Message-ID: <20170316201710.GN4085@HEDWIG.INI.CMU.EDU>
Date:   Thu, 16 Mar 2017 16:17:11 -0400
From:   "Gabriel L. Somlo" <gsomlo@...il.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v5 untested] kvm: better MWAIT emulation for guests

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