Re: [PATCH] x86/S3: Drop {save,restore}_rest_processor_state() completely

[Jan Beulich <jbeulich@suse.com>]

On 29.04.2020 15:36, Andrew Cooper wrote:
> On 29/04/2020 14:25, Jan Beulich wrote:
>> On 29.04.2020 13:32, Andrew Cooper wrote:
>>> On 29/04/2020 12:16, Jan Beulich wrote:
>>>> On 29.04.2020 13:09, Andrew Cooper wrote:
>>>>> --- a/xen/arch/x86/boot/trampoline.S
>>>>> +++ b/xen/arch/x86/boot/trampoline.S
>>>>> @@ -91,6 +91,11 @@ trampoline_protmode_entry:
>>>>>          and     %edi,%edx
>>>>>          wrmsr
>>>>>  1:
>>>>> +        /* Set up PAT before enabling paging. */
>>>>> +        mov     $XEN_MSR_PAT & 0xffffffff, %eax
>>>>> +        mov     $XEN_MSR_PAT >> 32, %edx
>>>>> +        mov     $MSR_IA32_CR_PAT, %ecx
>>>>> +        wrmsr
>>>> Doesn't this also eliminate the need for cpu_init() doing this?
>>>> If you agree with that one also dropped
>>>> Reviewed-by: Jan Beulich <jbeulich@suse.com>
>>> That doesn't cover the BSP on either the legacy or EFI paths.
>> The legacy path, afaict, uses it:
>>
>> .Lskip_realmode:
>>         /* EBX == 0 indicates we are the BP (Boot Processor). */
>>         xor     %ebx,%ebx
>>
>>         /* Jump to the common bootstrap entry point. */
>>         jmp     trampoline_protmode_entry
> 
> Oh, of course.
> 
>> The xen.efi entry path really should have the change you make
>> mirrored anyway.
> 
> Are you happy for it to go in efi_arch_post_exit_boot()?  We don't
> disable paging, but that is the point where we switch from the EFI
> pagetables to Xen's.

Yes, that's the most "symmetrical" place, I think.

Jan