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Re: [PATCH for 4.19?] x86/Intel: unlock CPUID earlier for the BSP
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 13 Jun 2024 17:53:02 +0200
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
- Delivery-date: Thu, 13 Jun 2024 15:53:13 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 13.06.2024 17:16, Roger Pau Monné wrote:
> On Thu, Jun 13, 2024 at 10:19:30AM +0200, Jan Beulich wrote:
>> @@ -315,16 +329,7 @@ static void cf_check early_init_intel(st
>> bootsym(trampoline_misc_enable_off) &
>> MSR_IA32_MISC_ENABLE_XD_DISABLE)
>> printk(KERN_INFO "re-enabled NX (Execute Disable)
>> protection\n");
>>
>> - /* Unmask CPUID levels and NX if masked: */
>> - rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
>> -
>> - disable = misc_enable & MSR_IA32_MISC_ENABLE_LIMIT_CPUID;
>> - if (disable) {
>> - wrmsrl(MSR_IA32_MISC_ENABLE, misc_enable & ~disable);
>> - bootsym(trampoline_misc_enable_off) |= disable;
>> - printk(KERN_INFO "revised cpuid level: %d\n",
>> - cpuid_eax(0));
>> - }
>> + intel_unlock_cpuid_leaves(c);
>
> Do you really need to call intel_unlock_cpuid_leaves() here?
>
> For the BSP it will be taken care in early_cpu_init(), and for the APs
> MSR_IA32_MISC_ENABLE it will be set as part of the trampoline with the
> disables from trampoline_misc_enable_off.
The way the original code works, it allows to deal with the BSP having the
bit clear, but some or all of the APs having it set. I simply didn't want
to break that property.
Jan
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