Re: [PATCH] kexec: force x86_64 arches to boot kdump kernels on boot cpu

[Ben Woodard <woodard@redhat.com>]

Eric W. Biederman wrote:
> Neil Horman <nhorman@redhat.com> writes:
>
> > > ..TIMER: vector=0x31 apic1=0 pin1=2 apic2=-1 pin2=-1
>
> Ben, what chipset is this?

nVidia MCP55 pro

It is the original version of 
http://www.supermicro.com/Aplus/motherboard/Opteron8000/MCP55/H8QM8-2.cfm

i.e. not the -2. However, they don't seem to advertise the original 
version. Supermicro assures me that they are practically the same but I 
haven't played with the -2 version yet.


> > Ok, I think from what I understand of what we're reading here, the apic2 = -1
> > and pin2 = -1 indicate that the 8259 has no direct connection to any cpu, which
> > means that on shutdown disable_IO_APIC should take us into virtual wire mode.
> > As such enabling the APIC early in boot should fix us, but more consisely,
> > rewriting the entry in the IOAPIC to deliver int0 to the only running cpu should
> > accomplish the same goal for this problem.  Does that sound reasonable (at least
> > as a test to ensure we understand the problem) to everyone?
>
> Close.  There are two options with virtual wire mode.  
> - Either the local apic is in virtual wire mode, and somehow the
>   legacy interrupts make it to the local cpu.
> - Or an ioapic is in virtual wire mode and the legacy interrupt
>   controller is connected to it.
>
> So I guess fundamentally for any SMP system that only supports the
> cpu being in local apic mode and only routes interrupts to the boot
> strap processor we could be in trouble.  That is what our current
> information about your system suggests.
>
> However most systems actually connect the i8254 PIC interrupt
> controller to the ioapic in virtual wire mode.  As I recall the
> standard mapping is to ioapic 0, pin 0.  With ioapic 0, pin 2 being
> the timer interrupt (Possibly it is the other way around).
>
> So as a test we could feed those values into ioapic_8259 and see
> if the kdump case works.  I believe we prefer putting the ioapic
> into virtual wire mode over putting the cpu into virtual wire
> mode.  We can only control which cpu receives the legacy interrupts if
> we are putting the ioapic in virtual wire mode.
>
> It may also be an interesting test to just enable the timer for the
> ioapic in early boot, as you have suggested.  I don't have a clue what
> that will do.
>
> Eric
>
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--
-ben
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