[RFC PATCH] ARM: uprobes need icache flush after xol write

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Tue, Apr 08, 2014 at 05:27:35PM +0200, Oleg Nesterov wrote:
> Sorry, I din't read the whole thread yet...
> 
> On 04/08, Russell King - ARM Linux wrote:
> > On Tue, Apr 08, 2014 at 09:05:49AM -0400, David Long wrote:
> > > Unfortunately copy_to_user_page() also needs a pointer to a vma struct
> > > so, while it presumably provides the model to follow, it can't simply be
> > > dropped in.
> >
> > Well, isn't this code doing the same thing as ptrace?  It seems to want
> > to modify a page in userspace of another process to change instructions
> > that are going to be executed. That's what ptrace does, and ptrace
> > already copes with all the issues there.
> 
> Yes, but it does get_user_pages(&vma) and thus it knows vma.
> 
> > Given that we've already solved that problem, wouldn't it be a good idea
> > if the tracing code would stop trying to reinvent broken solutions to
> > problems we have already solved?
> 
> But uprobes can't do this. Of course, I am not saying this is impossible,
> but it would be nice to avoid mmap_sem/find_vma/etc.
> 
> Almost nobody (iirc only sparc?) actually uses this "vma" arguments. And
> at least the supported architectures do not (at least this is what I think
> after the quick grep).
> 
> Perhaps we can rolerate the hack below?

This has no effect at fixing the reported problem though:

#define flush_icache_user_range(vma,page,addr,len) \
        flush_dcache_page(page)

so it results in no change.

The bigger question is... what is this function supposed to do?  It's
not been documented in Documentation/cachetlb.txt, and nothing in the
kernel refers to this function - it is completely unused.

I think let's start out by killing this function - the semantics of
this function have been lost, so it's not clear what it was supposed
to do in its original form.  Even going back to the start of git
history, it looks like it was never used outside arch code.

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