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Re: [PATCH v4 02/18] xen/riscv: introduce VMID allocation and manegement


  • To: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Thu, 25 Sep 2025 15:53:45 +0200
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  • Cc: Alistair Francis <alistair.francis@xxxxxxx>, Bob Eshleman <bobbyeshleman@xxxxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Thu, 25 Sep 2025 13:53:45 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 24.09.2025 16:25, Oleksii Kurochko wrote:
> 
> On 9/19/25 11:26 PM, Jan Beulich wrote:
>> On 17.09.2025 23:55, Oleksii Kurochko wrote:
>>> @@ -151,6 +152,8 @@ void __init noreturn start_xen(unsigned long bootcpu_id,
>>>   
>>>       gstage_mode_detect();
>>>   
>>> +    vmid_init();
>> Like for the earlier patch, I'm not convinced this is a function good
>> to call from the top-level start_xen(). The two functions sitting side
>> by side actually demonstrates the scalability issue pretty well.
> 
> In the case of vmid_init(), it could be a good place to call it here since
> vmid_init() is expected to be called once when a pCPU is booted. For the boot
> CPU, all "setup" functions are called in start_xen(), so vmid_init() could
> potentially be called there as well.
> 
> For other (non-boot) CPUs, vmid_init() could be called somewhere in the
> __cpu_up() code or at the CPU’s entry point.

And then perhaps many more functions. This simply doesn't scale well. See
how we have hvm_enable() for the boot CPU part of this, and then
{svm,vmx}_cpu_up() for the secondary CPUs.

Jan



 


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