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

[Keir Fraser <keir@xxxxxxx>]

Could you give more info on the bug, such as a backtrace? I wonder whether
this might be better fixed in some more elegant way. Also I can't eyeball
where map_domain_page() is being called during x2apic setup.

 Thanks,
 Keir

On 21/01/2011 12:21, "Zhang, Fengzhe" <fengzhe.zhang@xxxxxxxxx> wrote:

> x86:x2apic: Disable x2apic on x86-32 permanently
> 
> x2apic initialization on x86_32 uses vcpu pointer before it is initialized. As
> x2apic is unlikely to be used on x86_32, this patch disables x2apic
> permanently on x86_32. It also asserts the sanity of vcpu pointer before
> dereference to prevent further misuse.
> 
> Signed-off-by: Fengzhe Zhang <fengzhe.zhang@xxxxxxxxx>
> 
> diff -r 02c0af2bf280 xen/arch/x86/apic.c
> --- 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 )
> diff -r 02c0af2bf280 xen/arch/x86/x86_32/domain_page.c
> --- a/xen/arch/x86/x86_32/domain_page.c Mon Jan 17 18:05:52 2011 +0000
> +++ b/xen/arch/x86/x86_32/domain_page.c Wed Jan 19 03:24:16 2011 -0500
> @@ -53,6 +53,8 @@
>      perfc_incr(map_domain_page_count);
> 
>      v = mapcache_current_vcpu();
> +    /* Prevent vcpu pointer being used before initialize. */
> +    ASSERT((unsigned long)v != 0xfffff000);
> 
>      dcache = &v->domain->arch.mapcache;
>      vcache = &v->arch.mapcache;
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel