linux-kernel - Re: [PATCH v3 4/4] membarrier: riscv: Provide core serializing command

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Date: Wed, 24 Jan 2024 19:44:20 +0100
From: Andrea Parri <parri.andrea@...il.com>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu,
	paulmck@...nel.org, corbet@....net, mmaas@...gle.com,
	hboehm@...gle.com, striker@...ibm.com, charlie@...osinc.com,
	rehn@...osinc.com, linux-riscv@...ts.infradead.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/4] membarrier: riscv: Provide core serializing
 command

> > +# riscv uses xRET as return from interrupt and to return to user-space.
> > +#
> > +# Given that xRET is not core serializing, we rely on FENCE.I for providing
> > +# core serialization:
> > +#
> > +#  - by calling sync_core_before_usermode() on return from interrupt (cf.
> > +#    ipi_sync_core()),
> > +#
> > +#  - via switch_mm() and sync_core_before_usermode() (respectively, for
> > +#    uthread->uthread and kthread->uthread transitions) to go back to
> > +#    user-space.
> 
> I don't quite get the meaning of the sentence above. There seems to be a
> missing marker before "to go back".

Let's see.  Without the round brackets, the last part becomes:

  - via switch_mm() and sync_core_before_usermode() to go back to
    user-space.

This is indeed what I meant to say.  What am I missing?

  Andrea