Messages in this thread | | | Date | Tue, 30 Jun 2009 20:14:58 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH v4] enable x2APIC without interrupt remapping under KVM |
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On 06/30/2009 08:00 PM, Eric W. Biederman wrote: > Gleb Natapov<gleb@redhat.com> writes: > > >> On Tue, Jun 30, 2009 at 12:18:19AM -0700, Yinghai Lu wrote: >> >>> how about kexec second kernel in KVM ? >>> >>> x2apic_preenabled will be set in second kernel. >>> >>> >> By the way anybody knows why kexec does not use BIOS reset code >> (cmos 0xf offset) to jump into new kernel after hard reset? >> > > After a hard reset. That simply isn't possible. A hard > reset clears everything even memory. > >
So the jump-to-vector reset code cannot work on real hardware? It works in qemu, but of course that's easy.
> You might be able to get a full cpu reset but not a reset of the I/O > devices. > > The premise of kexec is that we are doing things on our own, and don't > get a 3rd piece of software involved that has not been heavily tested > on the path we want to use. Occassionally it is a pain to do everything > ourselves but at least when we do and we test it we know it is going > to work. > > Cpu designers lately seem fond of adding features that require all > kind of coordination to turn on and off. We handle the hardware > virtualization mode features now, and if x2apic has similar problems > being turned on and off I am certain we can handle that case in a > similar fashion. > > When we can my preference is to keep code like that out of the > kexec on panic path if we can figure out how to write the software > to do something reasonable. > > Once we figure out how to work without putting the interrupt controllers > in legacy mode to handle the timer interrupts I expect all kinds of > things will become simpler. >
I think it makes sense to add full reset support as a non-default option. Leaving hardware running and dmaing left and right has its risks.
-- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.
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