From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Nicholas Piggin <npiggin@gmail.com>
Cc: linux-arch <linux-arch@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH v2] powerpc: select ARCH_HAS_MEMBARRIER_SYNC_CORE
Date: Wed, 15 Jul 2020 08:27:15 -0400 (EDT) [thread overview]
Message-ID: <849841781.14062.1594816035327.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <20200715094829.252208-1-npiggin@gmail.com>
----- On Jul 15, 2020, at 5:48 AM, Nicholas Piggin npiggin@gmail.com wrote:
[...]
> index 47bd4ea0837d..a4704f405e8d 100644
> --- a/arch/powerpc/include/asm/exception-64s.h
> +++ b/arch/powerpc/include/asm/exception-64s.h
> @@ -68,6 +68,13 @@
> *
> * The nop instructions allow us to insert one or more instructions to flush the
> * L1-D cache when returning to userspace or a guest.
> + *
> + * powerpc relies on return from interrupt/syscall being context synchronising
> + * (which hrfid, rfid, and rfscv are) to support ARCH_HAS_MEMBARRIER_SYNC_CORE
> + * without additional additional synchronisation instructions. soft-masked
> + * interrupt replay does not include a context-synchronising rfid, but those
> + * always return to kernel, the context sync is only required for IPIs which
> + * return to user.
> */
> #define RFI_FLUSH_SLOT \
> RFI_FLUSH_FIXUP_SECTION; \
I suspect the statement "the context sync is only required for IPIs which return to
user." is misleading.
As I recall that we need more than just context sync after IPI. We need context sync
in return path of any trap/interrupt/system call which returns to user-space, else
we'd need to add the proper core serializing barriers in the scheduler, as we had
to do for lazy tlb on x86.
Or am I missing something ?
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
next prev parent reply other threads:[~2020-07-15 12:30 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-15 9:48 [PATCH v2] powerpc: select ARCH_HAS_MEMBARRIER_SYNC_CORE Nicholas Piggin
2020-07-15 10:08 ` Andreas Schwab
2020-07-16 0:56 ` Nicholas Piggin
2020-07-15 12:27 ` Mathieu Desnoyers [this message]
2020-07-16 0:57 ` Nicholas Piggin
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