[lkml]   [2018]   [Feb]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH] x86/microcode/intel: Use 64-bit arithmetic instead of 32-bit
On Tue, 13 Feb 2018, Gustavo A. R. Silva wrote:

> Add suffix ULL to constant 1024 in order to give the compiler complete
> information about the proper arithmetic to use. Notice that this
> constant is used in a context that expects an expression of type
> u64 (64 bits, unsigned).
> The expression c->x86_cache_size * 1024 is currently being evaluated
> using 32-bit arithmetic.
> Addresses-Coverity-ID: 1464429
> Signed-off-by: Gustavo A. R. Silva <>
> ---
> arch/x86/kernel/cpu/microcode/intel.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
> index f7c55b0..e5edb92 100644
> --- a/arch/x86/kernel/cpu/microcode/intel.c
> +++ b/arch/x86/kernel/cpu/microcode/intel.c
> @@ -982,7 +982,7 @@ static struct microcode_ops microcode_intel_ops = {
> static int __init calc_llc_size_per_core(struct cpuinfo_x86 *c)
> {
> - u64 llc_size = c->x86_cache_size * 1024;
> + u64 llc_size = c->x86_cache_size * 1024ULL;

x86_cache_size is 'int', so you really want to cast c->x86_cache_size to
(u64) for correctness sake.

Aside of that the patch is really purely cosmetic at the moment because the
largest LLC sizes are still below the 3 digit MB range which fits into
32bit quite well. You'd need to have a CPU with >= 2G LLC to create a

But looking at c->x86_cache_size again. It's int because it's set to -1
initially which is then changed if CPUid or general CPU info gives real
information about the cache size. The only place where that matters is the
/proc/cpuinfo output:

if (c->x86_cache_size >= 0)
seq_printf(m, "cache size\t: %d KB\n", c->x86_cache_size);

which is silly, because that really can be done with:

if (c->x86_cache_size)

as there is no point in printing 'cache size 0KB', which means
x86_cache_size can be made unsigned int, which makes sense because cache
size < 0 does not at all.

So instead of doing this purely mechanical cosmetic change to make a static
checker shut up, I'd like to see a proper cleanup of that thing.



 \ /
  Last update: 2018-02-13 18:03    [W:0.058 / U:2.168 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site