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Re: [Qemu-devel] [PATCH] add 'monitor' and 'mwait' instruction (update)


From: R. Armiento
Subject: Re: [Qemu-devel] [PATCH] add 'monitor' and 'mwait' instruction (update)
Date: Sat, 08 Jul 2006 15:16:40 +0200
User-agent: Thunderbird 1.5.0.4 (X11/20060615)

Hi,

Joachim Henke wrote:
Please use the updated patch attached below.

Great work! The patch fixes the kernel panic for me. Thank you.

However, as you probably know, despite not declaring MONITOR in qemu, kqemu sees MONITOR on the host processor and Linux CPU usage will still be 100%, even with your updated patch. So even with your patch applied one should use the 'idle=halt' kernel parameter when booting Linux with -kernel-kqemu on newer processors.

While your patch resolves the problem and is great for my setup, I suppose it is problematic. If MONITOR is not declared by qemu then still serving mwait 'correctly' is not faithful emulation (right?). To make sure this does not break anything else, I would guess that either mwait has to be emulated better so that it is ok to let qemu declare MONITOR support; OR as a temporary workaround make the patch only serve mwait if -kernel-kqemu is enabled and host CPUID supports MONITOR.

The whole thing with CPUID not being trappable seems like a can of worms to me, partly breaking hardware abstraction. I am totally ignorant of the inner workings of kqemu; but if it was somehow possible to "rewrite" CPUID into something trappable and handling it correctly, that would give a much more satisfying solution to this problem.

Rickard





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