Re: [Qemu-devel] [PATCH v2] hmp: allow cpu index for "info lapic"

[Eduardo Habkost]

On Wed, Jul 19, 2017 at 01:16:28PM +0100, Dr. David Alan Gilbert wrote:
> * Eduardo Habkost (address@hidden) wrote:
> > On Wed, Jul 19, 2017 at 12:47:53PM +0800, address@hidden wrote:
> > > Hi Eduardo,
> > > 
> > > Thank you for your reply!
> > > 
> > > >On Mon, Jul 17, 2017 at 09:49:37PM -0400, Yi Wang wrote:
> > > >> Add [vcpu] index support for hmp command "info lapic", which is
> > > >> useful when debugging ipi and so on. Current behavior is not
> > > >> changed when the parameter isn't specified.
> > > >> 
> > > >> Signed-off-by: Yi Wang <address@hidden>
> > > >> Signed-off-by: Yun Liu <address@hidden>
> > > >
> > > 
> > > >We have 8 monitor commands (see below) that use the CPU set by
> > > >the "cpu" command (mon_get_cpu()) as input.  Why is "info lapic"
> > > >special?
> > > 
> > > When we debugging a problem of ipi, we wanted to verify lapic info
> > > on each vCPU, but we found that we could only get vCPU 0's lapic
> > > through "info lapic", so we supposed this patch could help those
> > > who have the same problem as us.
> > 
> > The "cpu" command is supposed to allow you to select the CPU for
> > those commands.  Doesn't it work?
> 
> In the other arm to the thread Yi explained that they were driving
> it via virsh qemu-monitor-command,  and I've just tried and it
> doesn't seem to work; doing:
> 
> virsh  qemu-monitor-command --domain rhel6.8 --hmp --cmd "cpu 1"
> virsh  qemu-monitor-command --domain rhel6.8 --hmp --cmd "info lapic"
> dumping local APIC state for CPU 0

Right, the "cpu" command is useless inside a
'human-monitor-command' QMP command.  The 'cpu-index' argument
should be used instead. should make "cpu" print an error if ran
inside 'human-monitor-command' instead of silently pretend it
worked.

If virsh doesn't support the 'cpu-index' argument to
'human-monitor-command', it's possible to work around that
limitation by building your own QMP command.  e.g.:

  # virsh qemu-monitor-command f26test '{"execute":"human-monitor-command", 
"arguments":{"command-line":"info lapic", "cpu-index":1}}' | jq -r '.return'
  dumping local APIC state for CPU 1 
  
  LVT0     0x00010000 active-hi edge  masked                      Fixed  (vec 0)
  LVT1     0x00010000 active-hi edge  masked                      Fixed  (vec 0)
  LVTPC    0x00010000 active-hi edge  masked                      Fixed  (vec 0)
  LVTERR   0x00010000 active-hi edge  masked                      Fixed  (vec 0)
  LVTTHMR  0x00010000 active-hi edge  masked                      Fixed  (vec 0)
  LVTT     0x00010000 active-hi edge  masked         one-shot     Fixed  (vec 0)
  Timer    DCR=0x0 (divide by 2) initial_count = 0
  SPIV     0x000000ff APIC disabled, focus=off, spurious vec 255
  ICR      0x000000fd physical edge de-assert no-shorthand
  ICR2     0x00000000 cpu 0 (X2APIC ID)
  ESR      0x00000000
  ISR      (none)
  IRR      (none)
  
  APR 0x00 TPR 0x00 DFR 0x0f LDR 0x00 PPR 0x00


-- 
Eduardo