[PATCH] ARM: mm: avoid attempting to flush the gate_vma with VIVT caches

On 07/22/2012 03:03 PM, Will Deacon wrote:

On Sat, Jul 21, 2012 at 03:47:37PM +0100, Gilles Chanteperdrix wrote:

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On 07/21/2012 04:40 PM, Gilles Chanteperdrix wrote:

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On 07/21/2012 04:35 PM, Will Deacon wrote:

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Hi Gilles,

On Sat, Jul 21, 2012 at 02:18:35PM +0100, Gilles Chanteperdrix wrote:

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On 07/20/2012 10:41 PM, Gilles Chanteperdrix wrote:

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Being 0 or 1 whether we want to flush the vector page (I believe we do
not want to flush it, but am not sure).

Actually, I believe we want to flush the vector page, at least on
systems with VIVT cache: on systems with VIVT cache, the vector page is
writeable in kernel mode, so may have been modified, and the address
used by elf_core_dump is not the vectors address, but the address in the
kernel direct-mapped RAM region where the vector page was allocated, so
there is a cache aliasing issue.

It may be writable, but we never actually write to it after it has been
initialised so there's no need to worry about caching issues (the cache is
flushed in devicemaps_init).

Except if CONFIG_TLS_REG_EMUL is enabled

is disabled I mean.

Well spotted! I disagree about the address being flushed though -- it looks
to me like we flush from 0xffff0000 - 0xffff1000, which is what we want. Why
do you think we're flushing from the linear mapping?

I do not think we're flushing from the linear mapping, I believe the
address used by the elf_core_dump function (elf_core_dump -> kmap ->
page_address), to copy the page data to the core is the linear mapping
address, which is the reason why we need the flush at all.

-- 
                                                                Gilles.