Re: [Xen-devel] Workings/effectiveness of the xen-acpi-processor driver

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, May 02, 2012 at 06:09:26PM -0400, Boris Ostrovsky wrote:
> On 05/02/2012 05:41 PM, Konrad Rzeszutek Wilk wrote:
> >On Wed, May 02, 2012 at 02:31:07PM -0700, Boris Ostrovsky wrote:
> >>On 05/02/2012 01:14 PM, Konrad Rzeszutek Wilk wrote:
> >>>On Wed, May 02, 2012 at 01:06:34PM -0400, Boris Ostrovsky wrote:
> >>>>On 05/02/2012 12:08 PM, Konrad Rzeszutek Wilk wrote:
> >>>>>diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> >>>>>index a8f8844..d816448 100644
> >>>>>--- a/arch/x86/xen/enlighten.c
> >>>>>+++ b/arch/x86/xen/enlighten.c
> >>>>>@@ -811,7 +811,29 @@ static void xen_io_delay(void)
> >>>>>  #ifdef CONFIG_X86_LOCAL_APIC
> >>>>>  static u32 xen_apic_read(u32 reg)
> >>>>>  {
> >>>>>-        return 0;
> >>>>>+        struct xen_platform_op op = {
> >>>>>+                .cmd = XENPF_get_cpuinfo,
> >>>>>+                .interface_version = XENPF_INTERFACE_VERSION,
> >>>>>+                .u.pcpu_info.xen_cpuid = 0,
> >>>>
> >>>>
> >>>>Is this always zero? This will probably solve the current problem
> >>>
> >>>Its a CPU number (not tied in to APIC or ACPI IDs).
> >>
> >>Why not use CPU number instead of zero here?
> >
> >The issue was only with the bootup CPU - so was using the Xen's
> >bootup CPU number - which is zero (as is Linux's).
> 
> I agree that for this particular problem this may be sufficient.
> 
> My concern is that in the future someone may decide to use
> apic_read(APIC_ID) or read_apic_id() for some other purpose and they
> won't get expected result (i.e. on all CPUs they will get the same
> answer).

Good point. Let's get this particular bug fixed for v3.5, and then will
do a more comprehensive fix for v3.6.

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