Re: [PATCH v1 2/6] xen/riscv: introduce things necessary for p2m initialization

[Oleksii Kurochko <oleksii.kurochko@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 1201 bytes --]


On 6/5/25 4:19 PM, Jan Beulich wrote:
>>>> Won't be enough to flushing of guest TLB only during context switch?
>>> "only" is interesting here. Context switches are a relatively frequent
>>> operation, which in addition you want to be fast. If a flush is necessary
>>> there for correctness (e.g. when VMIDs aren't in use), you have to do it
>>> there. But if you can flush less frequently without violating correctness,
>>> you'd almost always want to use such an opportunity.
>> Then it is better to introduce VMID now, it seems it's only one place where
>> it should be set, when hgatp is initialized.
>>
>> Does Xen have some framework to work with VMID?
> That's all arch-specific, I think.

Probably, I used incorrect words to express what I want. I wrote about allocation/freeing
of VMIDs. Basically something similar to what Arm has (|p2m_vmid_allocator_init(), ||p2m_alloc_vmid(), ||p2m_free_vmid|):
   https://gitlab.com/xen-project/xen/-/blob/staging/xen/arch/arm/p2m.c?ref_type=heads#L271

It seems like it is not very arch-specific, at the moment.

But, likely, RISC-V will need to do an update|p2m_alloc_vmid(), which will do p2m's TLB flush when overflow of VMIDs 
happen. ~ Oleksii |

[-- Attachment #2: Type: text/html, Size: 2085 bytes --]