Re: [kvm-unit-tests PATCH] x86: Reset lapic after boot

[Krish Sadhukhan <krish.sadhukhan@oracle.com>]

On 6/25/19 5:10 AM, Nadav Amit wrote:
> Do not assume that the local APIC is in a xAPIC mode after reset.
> Instead reset it first, since it might be in x2APIC mode, from which a
> transition in xAPIC is invalid.
>
> Note that we do not use the existing disable_apic() for the matter,
> since it also re-initializes apic_ops.


Is there any issue if apic_ops is reset ?


>
> Signed-off-by: Nadav Amit <nadav.amit@gmail.com>
> ---
>   x86/cstart64.S | 11 +++++++++++
>   1 file changed, 11 insertions(+)
>
> diff --git a/x86/cstart64.S b/x86/cstart64.S
> index 9791282..03726a6 100644
> --- a/x86/cstart64.S
> +++ b/x86/cstart64.S
> @@ -118,6 +118,15 @@ MSR_GS_BASE = 0xc0000101
>   	wrmsr
>   .endm
>   
> +lapic_reset:
> +	mov $0x1b, %ecx


Why not use MSR_IA32_APICBASE instead of 0x1b ?


> +	rdmsr
> +	and $~(APIC_EN | APIC_EXTD), %eax
> +	wrmsr
> +	or $(APIC_EN), %eax
> +	wrmsr
> +	ret
> +
>   .macro setup_segments
>   	mov $MSR_GS_BASE, %ecx
>   	rdmsr
> @@ -228,6 +237,7 @@ save_id:
>   	retq
>   
>   ap_start64:
> +	call lapic_reset
>   	call load_tss
>   	call enable_apic
>   	call save_id
> @@ -240,6 +250,7 @@ ap_start64:
>   	jmp 1b
>   
>   start64:
> +	call lapic_reset
>   	call load_tss
>   	call mask_pic_interrupts
>   	call enable_apic