Re: [Qemu-devel] [PATCH] Add e500 instructions dcblc, dcbtls and dcbtstl as no-op

[Scott Wood]

On Fri, 1 Jul 2011 00:18:22 +0200
Alexander Graf <address@hidden> wrote:

> 
> On 01.07.2011, at 00:11, Scott Wood wrote:
> 
> > Almost, but what if we have write permission but not read?
> 
> How would you write back data from a cache line when you haven't read it 
> earlier?

The CPU can read it.  The program can't.

> > but what about a race with DMA from the I/O thread?
> 
> That'd simply be broken, but I don't quite see how it wouldn't with real 
> hardware either :).

Real hardware doesn't generate a load/store sequence that the program didn't
ask for -- where's the breakage?

-Scott