Re: [Xen-devel] [PATCH]x86:x2apic: Disable x2apic on x86-32 permanently

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 21.01.11 at 13:21, "Zhang, Fengzhe" <fengzhe.zhang@xxxxxxxxx> wrote:
> --- a/xen/arch/x86/apic.c     Mon Jan 17 18:05:52 2011 +0000
> +++ b/xen/arch/x86/apic.c     Wed Jan 19 03:24:16 2011 -0500
> @@ -961,6 +961,22 @@
>      if ( !cpu_has_x2apic )
>          return;
> 
> +#ifdef __i386__
> +    clear_bit(X86_FEATURE_X2APIC, boot_cpu_data.x86_capability);
> +    if (x2apic_enabled) {
> +        uint64_t msr_content;
> +
> +        rdmsrl(MSR_IA32_APICBASE, msr_content);
> +        msr_content &= ~(MSR_IA32_APICBASE_ENABLE | MSR_IA32_APICBASE_EXTD);
> +        wrmsrl(MSR_IA32_APICBASE, msr_content);
> +        msr_content |= MSR_IA32_APICBASE_ENABLE;
> +        wrmsrl(MSR_IA32_APICBASE, msr_content);
> +        x2apic_enabled = 0;
> +    }
> +    printk("x2APIC disabled permanently on x86_32.\n");
> +    return;
> +#endif
> +
>      if ( !opt_x2apic )
>      {
>          if ( !x2apic_enabled )

How does this (namely the x2apic_enabled part) play together
with the selection of the APIC driver, which in this case would
have happened quite a bit earlier (from generic_apic_probe())?

I would therefore think that this change really belongs into
check_x2apic_preenabled().

Jan


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