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Re: [PATCH v2 1/2] x86/boot: Clear XD_DISABLE from the early boot path
- To: Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 22 Jun 2023 09:54:01 +0200
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Delivery-date: Thu, 22 Jun 2023 07:54:13 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 21.06.2023 18:43, Alejandro Vallejo wrote:
> Sure, to everything before this
>
>>> diff --git a/xen/arch/x86/cpu/intel.c b/xen/arch/x86/cpu/intel.c
>>> index 168cd58f36..46b0cd8dbb 100644
>>> --- a/xen/arch/x86/cpu/intel.c
>>> +++ b/xen/arch/x86/cpu/intel.c
>>> @@ -305,23 +305,23 @@ static void cf_check early_init_intel(struct
>>> cpuinfo_x86 *c)
>>> c->x86_cache_alignment = 128;
>>>
>>> /* Unmask CPUID levels and NX if masked: */
>>> - rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
>>> -
>>> - disable = misc_enable & (MSR_IA32_MISC_ENABLE_LIMIT_CPUID |
>>> - MSR_IA32_MISC_ENABLE_XD_DISABLE);
>>> - if (disable) {
>>> - wrmsrl(MSR_IA32_MISC_ENABLE, misc_enable & ~disable);
>>> - bootsym(trampoline_misc_enable_off) |= disable;
>>> - bootsym(trampoline_efer) |= EFER_NXE;
>>> - }
>>> + if (rdmsr_safe(MSR_IA32_MISC_ENABLE, misc_enable) == 0) {
>>
>> There's no need to change rdmsrl() to rdmsr_safe(),
> I thought we established before some hypervisors might not implement it. In
> that case this function would crash. More gracefully than a triple fault,
> sure, but still not a very friendly thing to do.
Yet then in early boot code you also don't (and can't) recover from getting
#GP(0), in case that might really happen.
Jan
|
