Re: [PATCH v14 11/13] x86/mm: do targeted broadcast flushing from tlbbatch code

[Borislav Petkov]

On Tue, Mar 04, 2025 at 12:52:47PM +0000, Brendan Jackman wrote:
> https://lore.kernel.org/all/CA+i-1C31TrceZiizC_tng_cc-zcvKsfXLAZD_XDftXnp9B2Tdw@xxxxxxxxxxxxxx/

Lemme try to understand what you're suggesting on that subthread:

> static inline void arch_start_context_switch(struct task_struct *prev)
> {
>     arch_paravirt_start_context_switch(prev);
>     tlb_start_context_switch(prev);
> }

This kinda makes sense to me...

> Now I think about it... if we always tlbsync() before a context switch, is the
> cant_migrate() above actually required? I think with that, even if we migrated
> in the middle of e.g.  broadcast_kernel_range_flush(), we'd be fine? (At
> least, from the specific perspective of the invplgb code, presumably having
> preemption on there would break things horribly in other ways).

I think we still need it because you need to TLBSYNC on the same CPU you've
issued the INVLPGB and actually, you want all TLBs to have been synched
system-wide.

Or am I misunderstanding it?

Anything else I missed?

Btw, I just sent v15 - if you wanna continue commenting there...

https://lore.kernel.org/r/20250304135816.12356-1-bp@xxxxxxxxxx

Thx.

-- 
Regards/Gruss,
    Boris.

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