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

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

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