Re: [Xen-devel] [PATCH 1/2] xen/apic: Provide Xen-specific version of cpu_present_to_apicid APIC op

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

On Thu, Mar 17, 2016 at 09:03:24AM -0400, Boris Ostrovsky wrote:
> Currently Xen uses default_cpu_present_to_apicid() which will always
> report BAD_APICID for PV guests since x86_bios_cpu_apic_id is initialised
> to that value and is never updated.
> 
> With commit 1f12e32f4cd5 ("x86/topology: Create logical package id"), this
> op is now called by smp_init_package_map() when deciding whether to call
> topology_update_package_map() which sets cpu_data(cpu).logical_proc_id.
> The latter (as topology_logical_package_id(cpu)) may be used, for example,
> by cpu_to_rapl_pmu() as an array index. Since uninitialized
> logical_package_id is set to -1, the index will become 64K which is
> obviously problematic.
> 
> While RAPL code (and any other users of logical_package_id) should be
> careful in their assumptions about id's validity, Xen's
> cpu_present_to_apicid op should still provide value consistent with its
> own xen_apic_read(APIC_ID).
> 
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

> ---
>  arch/x86/xen/apic.c |   12 ++++++++++--
>  1 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/xen/apic.c b/arch/x86/xen/apic.c
> index abf4901..db52a7f 100644
> --- a/arch/x86/xen/apic.c
> +++ b/arch/x86/xen/apic.c
> @@ -66,7 +66,7 @@ static u32 xen_apic_read(u32 reg)
>  
>       ret = HYPERVISOR_platform_op(&op);
>       if (ret)
> -             return 0;
> +             op.u.pcpu_info.apic_id = BAD_APICID;
>  
>       return op.u.pcpu_info.apic_id << 24;
>  }
> @@ -142,6 +142,14 @@ static void xen_silent_inquire(int apicid)
>  {
>  }
>  
> +static int xen_cpu_present_to_apicid(int cpu)
> +{
> +     if (cpu_present(cpu))
> +             return xen_get_apic_id(xen_apic_read(APIC_ID));
> +     else
> +             return BAD_APICID;
> +}
> +
>  static struct apic xen_pv_apic = {
>       .name                           = "Xen PV",
>       .probe                          = xen_apic_probe_pv,
> @@ -162,7 +170,7 @@ static struct apic xen_pv_apic = {
>  
>       .ioapic_phys_id_map             = default_ioapic_phys_id_map, /* Used 
> on 32-bit */
>       .setup_apic_routing             = NULL,
> -     .cpu_present_to_apicid          = default_cpu_present_to_apicid,
> +     .cpu_present_to_apicid          = xen_cpu_present_to_apicid,
>       .apicid_to_cpu_present          = physid_set_mask_of_physid, /* Used on 
> 32-bit */
>       .check_phys_apicid_present      = default_check_phys_apicid_present, /* 
> smp_sanity_check needs it */
>       .phys_pkg_id                    = xen_phys_pkg_id, /* detect_ht */
> -- 
> 1.7.1
> 

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