Re: [PATCH v3 1/4] sparc64: NG4 memset 32 bits overflow

[Andrew Morton <akpm@linux-foundation.org>]

On Thu,  2 Mar 2017 00:33:42 -0500 Pavel Tatashin <pasha.tatashin@oracle.com> wrote:

> Early in boot Linux patches memset and memcpy to branch to platform
> optimized versions of these routines. The NG4 (Niagra 4) versions are
> currently used on  all platforms starting from T4. Recently, there were M7
> optimized routines added into UEK4 but not into mainline yet. So, even with
> M7 optimized routines NG4 are still going to be used on T4, T5, M5, and M6
> processors.
> 
> While investigating how to improve initialization time of dentry_hashtable
> which is 8G long on M6 ldom with 7T of main memory, I noticed that memset()
> does not reset all the memory in this array, after studying the code, I
> realized that NG4memset() branches use %icc register instead of %xcc to
> check compare, so if value of length is over 32-bit long, which is true for
> 8G array, these routines fail to work properly.
> 
> The fix is to replace all %icc with %xcc in these routines. (Alternative is
> to use %ncc, but this is misleading, as the code already has sparcv9 only
> instructions, and cannot be compiled on 32-bit).
> 
> This is important to fix this bug, because even older T4-4 can have 2T of
> memory, and there are large memory proportional data structures in kernel
> which can be larger than 4G in size. The failing of memset() is silent and
> corruption is hard to detect.
> 
> Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
> Reviewed-by: Babu Moger <babu.moger@oracle.com>

It sounds like this fix should be backported into -stable kernels?  If
so, which version(s)?

Also, what are the user-visible runtime effects of this change?

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