Re: [Xen-devel] xen/arm and swiotlb-xen: possible data corruption

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

On 02/03/17 19:12, Stefano Stabellini wrote:
> On Thu, 2 Mar 2017, Julien Grall wrote:
> > On 02/03/17 08:53, Edgar E. Iglesias wrote:
> > > On Thu, Mar 02, 2017 at 09:38:37AM +0100, Edgar E. Iglesias wrote:
> > > > On Wed, Mar 01, 2017 at 05:05:21PM -0800, Stefano Stabellini wrote:
> Julien, from looking at the two diffs, this is simpler and nicer, but if
> you look at xen/include/asm-arm/page.h, my patch made
> clean_dcache_va_range consistent with invalidate_dcache_va_range. For
> consistency, I would prefer to deal with the two functions the same way.
> Although it is not a spec requirement, I also think that it is a good
> idea to issue cache flushes from cacheline aligned addresses, like
> invalidate_dcache_va_range does and Linux does, to make more obvious
> what is going on.
invalid_dcache_va_range is split because the cache instruction differs 
for the start and end if unaligned. For them you want to use clean & 
invalidate rather than invalidate.
If you look at the implementation of other cache helpers in Linux (see 
dcache_by_line_op in arch/arm64/include/asm/assembler.h), they will only 
align start & end.
Also, the invalid_dcache_va_range is using modulo which I would rather 
avoid. The modulo in this case will not be optimized by the compiler 
because cacheline_bytes is not a constant.
So I still prefer to keep this function really simple.

BTW, you would also need to fix clean_and_invalidate_dcache_va_range.

--
Julien Grall

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