Re: [PATCH] x86/microcode/intel: Use 64-bit arithmetic instead of 32-bit
On Tue, 13 Feb 2018, Alan Cox wrote: > > 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. > > Currently 0MB means "I know you have no cache" (early slot 1 celeron), > while not printing it means 'I have no clue' Cute. I hope the 3 slot1 celeron users will not go wild if their /proc/cpuinfo now claims to have no clue about caches. Thanks, tglx
Re: [PATCH] x86/microcode/intel: Use 64-bit arithmetic instead of 32-bit
> 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. Currently 0MB means "I know you have no cache" (early slot 1 celeron), while not printing it means 'I have no clue' Alan
Re: [PATCH] x86/microcode/intel: Use 64-bit arithmetic instead of 32-bit
Hi Thomas,
Quoting Thomas Gleixner :
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
problem.
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.
Yeah, actually I was curious about why x86_cache_size is signed
instead of unsigned. You've made it clear now.
I will change it to be of type unsigned int and make the proper
changes to the rest of code in which x86_cache_size is being used.
Also, I'm curious about the types of the rest of the related variables:
/* Cache QoS architectural values: */
int x86_cache_max_rmid; /* max index */
int x86_cache_occ_scale;/* scale to bytes */
int x86_power;
Maybe they need some cleanup too.
Thanks for the feedback.
--
Gustavo
Re: [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
problem.
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.
Thanks,
tglx
[PATCH] x86/microcode/intel: Use 64-bit arithmetic instead of 32-bit
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;
do_div(llc_size, c->x86_max_cores);
--
2.7.4
