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

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Message-ID: <20170316192440.GL4085@HEDWIG.INI.CMU.EDU>
Date:   Thu, 16 Mar 2017 15:24:41 -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 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>"

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