Re: [RFC PATCH 4/7] x86: use exit_lazy_tlb rather than membarrier_mm_sync_core_before_usermode

----- On Jul 13, 2020, at 9:47 AM, Nicholas Piggin npiggin@gmail.com wrote:

Excerpts from Nicholas Piggin's message of July 13, 2020 2:45 pm:

quoted

Excerpts from Andy Lutomirski's message of July 11, 2020 3:04 am:

quoted

Also, as it stands, I can easily see in_irq() ceasing to promise to
serialize.  There are older kernels for which it does not promise to
serialize.  And I have plans to make it stop serializing in the
nearish future.

You mean x86's return from interrupt? Sounds fun... you'll konw where to
update the membarrier sync code, at least :)

Oh, I should actually say Mathieu recently clarified a return from
interrupt doesn't fundamentally need to serialize in order to support
membarrier sync core.

Clarification to your statement:

Return from interrupt to kernel code does not need to be context serializing
as long as kernel serializes before returning to user-space.

However, return from interrupt to user-space needs to be context serializing.

Thanks,

Mathieu

https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-July/214171.html

So you may not need to do anything more if you relaxed it.

Thanks,
Nick

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com