arm64: Question about barriers with the mmu off

[Valdis Kl=?utf-8?Q?=c4=93?=tnieks]

On Mon, 16 Nov 2020 20:58:52 +0900, Wonhyuk Yang said:

> str w0, [x1]
So we dirtied the cache line.
> dmb sys
> dc ivac, x1   // Invalidate potentially stale cache line

So we invalidate it.

> Is there any problem, if the dc operation precedes the store operation?

If you swap them, you get...

dc ivac,x1   // invalidate a cache line that's probably OK
str w0,[x1   // and now we do a store that leaves a possibly stale cache line

In other words, if you swap them you may leave an un-invalidated
stale cache line.

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