Re: [RFC PATCH] ARM: Add imprecise abort enable/disable macro

[Fabrice Gasnier]

On 02/10/2014 04:24 PM, Russell King - ARM Linux wrote:
> On Mon, Feb 10, 2014 at 03:12:47PM +0000, Dave Martin wrote:
> > Firstly, blindly adding 4 to PC is obviouly not right, partly because we
> > might be running an unrelated thread by the time the abort fires, and
> > also because the affected instruction might not be 4 bytes in size in a
> > Thumb kernel.
> Exactly.  We ended up on some platforms having special accessors for PCI
> where we included a number of 'mov r0, r0' instructions after the accessor
> so we could properly cope with them - but this required knowledge that
> we were going to only receive an imprecise abort from these accessors
> and only for a few cycles after the instruction.
>
> However, that's not true with modern architectures.  The point they're
> received will _not_ be the load/store which resulted in the abort, and
> in the case of a write, they could be many hundreds of cycles later,
> especially if the write has been buffered.
What about putting a memory barrier after a load/store ?
CPU should wait for the operation to complete right ?
> So adding four to the PC is definitely a very /bad/ thing to do.

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