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Re: [Qemu-devel] Re: [RESENT][PATCH 2/2] x86: Issue reset on triple faul


From: Natalia Portillo
Subject: Re: [Qemu-devel] Re: [RESENT][PATCH 2/2] x86: Issue reset on triple faults
Date: Mon, 23 Jun 2008 21:01:52 +0100
User-agent: Thunderbird 2.0.0.14 (Windows/20080421)

A CMOS byte?

Is there really a way to distinguish between wanted reset-by-triple-fault or a non-wanted-triple-fault?

As far as I know the first guest that used this for context switching (OS/2 1.x) used it as an undocumented but convenient bug/feature of 286 cpu.

Jamie Lokier escribió:
Jan Kiszka wrote:
It might be worth distinguishing between
triple-fault-used-by-guest-for-context-switch and triple faults which
trigger a normal reset, and log only the latter.  There's a
standardish way of distinguishing them, which the BIOS should check.
You refer to setting some return address at some magic BIOS location?

Probably; I forget the details.  There might be a CMOS byte, too.

Isn't this something the BIOS should handle, not QEMU?

The BIOS should handle it, yes.  But since it is standard behaviour,
it might be useful for QEMU to decide whether to _log_ the event as a
system reset based on that state.

Same for keyboard controller induced reset - that's also used for
context switching, in the same way.  (Triple fault is only used
because it's faster.)

Same also for deciding whether -no-reboot should close down the QEMU
process.  Now I think about it, that is the best reason to distinguish
them!

When helper(SVM_EXIT_SHUTDOWN, 0) is called, should it still also call
qemu_system_reset_request()?
helper_vmexit() is not expected to return (cpu_loop_exit).

Ok.  It's not clear unless you know the code, which I don't.  Just
wanted to check :-)

-- Jamie








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