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

["R. Armiento" <reply-2006@armiento.net>]

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