Re: [PATCH] KVM: Add missing emulation failure report in kvm_mmu_page_fault()

[Sheng Yang <sheng@linux.intel.com>]

On Monday 18 January 2010 19:32:14 Avi Kivity wrote:
> On 01/18/2010 11:32 AM, Sheng Yang wrote:
> > On Sunday 17 January 2010 20:34:23 Avi Kivity wrote:
> >> On 01/15/2010 10:44 AM, Sheng Yang wrote:
> >>> Currently we only have handle_invalid_guest_state() reported emulation
> >>> failure...
> >>
> >> This is intentional - instead of spamming dmesg, we exit with an
> >> internal error.  Modern qemu-kvm will halt and allow the user to inspect
> >> the guest with the built-in disassembler.
> >
> > I think keep it there still useful for some users. And we have the same
> > report in handle_invalid_guest_state(), and we even have "emulation
> > failure, check dmesg for details" in QEmu when handling
> > KVM_INTERNAL_ERROR_EMULATION.
> >
> > I think add one line here is the easiest way to keep consistence, and is
> > handy.
> 
> Another way to keep consistency is to remove emulation failure reporting
> in handle_invalid_guest_state() :)

OK, I would remove it...
 
> There are two problems with the kernel failure report.  First, it
> doesn't report enough data - registers, surrounding instructions, etc.
> that are needed to explain what is going on.  Second, it can flood
> dmesg, which is a pretty bad thing to do.
 
When you talking about "built-in disassembler", do you talking about 
"memsave/objdump" or some other more convenient way for this?

And maybe we can let QEmu do some dump of the assembler code? 
(kvm_show_code())

> I have a patch somewhere that adds instruction emulation bytes (both
> successful and failed) to ftrace.  That may be useful, perhaps.

It would surely help. :)

-- 
regards
Yang, Sheng