From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH RFC 27/31] xen/x86: Rework Intel
	masking/faulting setup
Date: Fri, 22 Jan 2016 14:46:20 +0000
Message-ID: <56A240BC.50900@citrix.com>
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To: Jan Beulich <JBeulich@suse.com>
Cc: Xen-devel <xen-devel@lists.xen.org>
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On 22/01/16 14:29, Jan Beulich wrote:
>>>> On 22.01.16 at 15:09, <andrew.cooper3@citrix.com> wrote:
>> On 22/01/16 09:40, Jan Beulich wrote:
>>>>>> On 16.12.15 at 22:24, <andrew.cooper3@citrix.com> wrote:
>>>> @@ -183,22 +237,13 @@ static void early_init_intel(struct cpuinfo_x86 *c)
>>>>  	    (boot_cpu_data.x86_mask == 3 || boot_cpu_data.x86_mask == 4))
>>>>  		paddr_bits = 36;
>>>>  
>>>> -	if (c == &boot_cpu_data && c->x86 == 6) {
>>>> -		if (probe_intel_cpuid_faulting())
>>>> -			__set_bit(X86_FEATURE_CPUID_FAULTING,
>>>> -				  c->x86_capability);
>>>> -	} else if (boot_cpu_has(X86_FEATURE_CPUID_FAULTING)) {
>>>> -		BUG_ON(!probe_intel_cpuid_faulting());
>>>> -		__set_bit(X86_FEATURE_CPUID_FAULTING, c->x86_capability);
>>>> -	}
>>>> +	if (c == &boot_cpu_data)
>>>> +		intel_init_levelling();
>>>> +
>>>> +	if (test_bit(X86_FEATURE_CPUID_FAULTING, boot_cpu_data.x86_capability))
>>>> +            __set_bit(X86_FEATURE_CPUID_FAULTING, c->x86_capability);
>>> So you intentionally delete the validation of CPUID faulting being
>>> available on APs?
>> Yes.  All this does is change where Xen crashes, in the case that AP's
>> have different capabilities to the BSP, and allows more startup code to
>> move into __init.
> So where did that Xen crash point move to (since I didn't spot it)?

set_cpuid_faulting() doesn't use safe MSR accesses, so would crash on
first use in a mixed setup.

I could extend it to ASSERT(cpu_has_cpuid_faulting) if you would prefer.

~Andrew