linux-kernel - Re: [PATCH 1/3] Loongson-2F: Flush the branch target history such as BTB and RAS

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Message-ID: <20100311095944.GC18065@linux-mips.org>
Date:	Thu, 11 Mar 2010 10:59:44 +0100
From:	Ralf Baechle <ralf@...ux-mips.org>
To:	Shinya Kuribayashi <shinya.kuribayashi@...el.com>
Cc:	Wu Zhangjin <wuzhangjin@...il.com>, Greg KH <gregkh@...e.de>,
	linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] Loongson-2F: Flush the branch target history such as
 BTB and RAS

On Thu, Mar 11, 2010 at 12:27:42PM +0900, Shinya Kuribayashi wrote:

> Are you sure that RAS represents "Row Address Strobe", not "Return
> Address Stack?"
> 
> By the way, we have a similar local workaround for vr55xx processors
> when switching from kernel mode to user mode.  It's not necessarily
> related to out-of-order issues, but we need to prevent the processor
> from doing instruction prefetch beyond "eret" instruction.

Some R4000 revisions may do silly things in case of an NMI where c0_errorepc
is pointing is pointing to an ERET instruction.

There are various processors which want to save and restore core-specific
registers, for example the Cavium cnMIPS core.

> In the long term, it would be appreciated that the kernel has a set
> of hooks when switching KUX-modes, so that each machine could have
> his own, processor-specific treatmens.

It seems that uasm is the tool of choice.

  Ralf
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