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Re: [PATCH v2 4/4] xen/arm: mpu: Implement a dummy enable_secondary_cpu_mm
- To: Ayan Kumar Halder <ayankuma@xxxxxxx>, Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 24 Sep 2024 14:22:04 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 24 Sep 2024 12:22:12 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 24.09.2024 13:54, Ayan Kumar Halder wrote:
> Hi Jan,
>
> On 23/09/2024 11:23, Jan Beulich wrote:
>> On 18.09.2024 19:51, Ayan Kumar Halder wrote:
>>> Secondary cpus initialization is not yet supported. Thus, we print an
>>> appropriate message and put the secondary cpus in WFE state.
>>>
>>> Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
>>> ---
>>> Changes from :-
>>>
>>> v1 - 1. NR_CPUS is defined as 1 for MPU
>> Not quite, what you do is ...
>>
>>> --- a/xen/arch/Kconfig
>>> +++ b/xen/arch/Kconfig
>>> @@ -11,6 +11,7 @@ config NR_CPUS
>>> default "8" if ARM && RCAR3
>>> default "4" if ARM && QEMU
>>> default "4" if ARM && MPSOC
>>> + default "1" if ARM && MPU
>>> default "128" if ARM
>>> help
>>> Controls the build-time size of various arrays and bitmaps
>> ... merely set the default. I wonder how useful that is, the more that
>> - as per the description - this is temporary only anyway.
>
> Yes, I can enforce a build time check like this.
>
> --- a/xen/arch/arm/setup.c
> +++ b/xen/arch/arm/setup.c
> @@ -295,6 +295,12 @@ void asmlinkage __init start_xen(unsigned long
> fdt_paddr)
> struct domain *d;
> int rc, i;
>
> + /*
> + * Currently MPU does not support SMP.
> + */
> +#ifdef CONFIG_MPU
> + BUILD_BUG_ON(NR_CPUS > 1);
> +#endif
> dcache_line_bytes = read_dcache_line_bytes();
>
> Does this look ok ?
Well, I'd still want to understand the purpose (if I was maintainer of
this code at least). You can't bring up secondary processors yet - fine.
But why does that mean you want to limit the build to NR_CPUS=1? Any
number is fine, but just not useful?
Jan
|
