On Tue, Nov 17, 2020 at 12:45 PM Valdis Klētnieks <valdis.kletnieks@vt.edu> wrote:
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.
You mean, even if STCLR_EL1.{C, M} is cleared, store doesn't bypass the cache?
That's the problem. The store bypasses the cache line, and the next reference that uses the cache can get stale data. So you have to flush the cache line so the next reference has to refresh the cache on the memory read.
Yes, I understood that I have to flush the cache before the cacheable read(mmu on). But I'm not fully understand your explanation below.
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
Could you explain me why the store still leaves stale cache? We invalidated the cacheline and store will not make footprint in the cache.