Re: flush_icache_range

[Kanoj Sarcar <kanoj@google.engr.sgi.com>]

> 
> On Sat, Jul 22, 2000 at 06:07:08PM -0700, Kanoj Sarcar wrote:
> 
> > Can anyone point out the logic of continued existance of flush_icache_range
> > after the introduction of flush_icache_page()? I admit that 
> > flush_icache_range is still needed in the module loading code, but do we
> > need it anymore in the a.out loading code? That code should be incurring
> > page faults, which will do the flush_icache_page anyway. Seems like
> > double work to me to do flush_icache_range again after the loading has
> > been done.
> 
> binfmt_elf.c:load_aout_interp() uses file->f_op->read to read the interpreter
> from disk, so actually need to use something else to flush the cache.
> Similar for two of three cases in binfmt_aout.c.  For these the page
> fault won't sufficiently flush cashes.

Okay, got it. flush_icache_page() can flush the icache, then 
flush_icache_range() can writeback-invalidate the dcache (for the a.out
section loading code), and things should work. AFAICS, this would be
the most optimal way to do things (ie, you don't have to writeback-invalidate
dcache, and invalidate icache in flush_icache_range(), you can optimize
out the icache flush relying on flush_icache_page to do the work).

> 
> > This argument to delete the flush_icache_range calls from the a.out
> > loading code assumes that the f_op->read() code behaves sanely, ie does
> > not do unexpected things like touch the user address (thus allocating
> > the page, and doing the icache flush via the page fault handler much
> > earlier) before it starts reading the a.out sections in ...
> 
> There is another MIPS specific problem with this routine.  Originally
> introduced for kernel modules the various incarnations of flush_icache_range
> are not protected against access from userspace.  Unable to handle kernel
> paging request ahead ...

Could you elaborate? Use mips as an example. Note: for the a.out code,
there will be one thread, and for the module loading, userspace access 
to the vmalloced area is not possible.

Kanoj
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