2020-01-14 21:09:12

by Michael Bringmann

Subject: [PATCH] Fix display of Maximum Memory

Correct overflow problem in calculation+display of Maximum Memory
value to syscfg where 32bits is insufficient.

Signed-off-by: Michael Bringmann <[email protected]>
---
arch/powerpc/platforms/pseries/lparcfg.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/lparcfg.c b/arch/powerpc/platforms/pseries/lparcfg.c
index 4ee2594..183aeb7 100644
--- a/arch/powerpc/platforms/pseries/lparcfg.c
+++ b/arch/powerpc/platforms/pseries/lparcfg.c
@@ -435,12 +435,12 @@ static void parse_em_data(struct seq_file *m)

static void maxmem_data(struct seq_file *m)
{
- unsigned long maxmem = 0;
+ unsigned long long maxmem = 0;

- maxmem += drmem_info->n_lmbs * drmem_info->lmb_size;
- maxmem += hugetlb_total_pages() * PAGE_SIZE;
+ maxmem += (unsigned long long)drmem_info->n_lmbs * (unsigned long long)drmem_info->lmb_size;
+ maxmem += (unsigned long long)hugetlb_total_pages() * (unsigned long long)PAGE_SIZE;

- seq_printf(m, "MaxMem=%ld\n", maxmem);
+ seq_printf(m, "MaxMem=%llu\n", maxmem);
}

static int pseries_lparcfg_data(struct seq_file *m, void *v)
--
1.8.3.1

2020-01-15 05:43:31

by Christophe Leroy

Subject: Re: [PATCH] Fix display of Maximum Memory

Le 14/01/2020 à 22:07, Michael Bringmann a écrit :
> Correct overflow problem in calculation+display of Maximum Memory
> value to syscfg where 32bits is insufficient.
>
> Signed-off-by: Michael Bringmann <[email protected]>
> ---
> arch/powerpc/platforms/pseries/lparcfg.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/platforms/pseries/lparcfg.c b/arch/powerpc/platforms/pseries/lparcfg.c
> index 4ee2594..183aeb7 100644
> --- a/arch/powerpc/platforms/pseries/lparcfg.c
> +++ b/arch/powerpc/platforms/pseries/lparcfg.c
> @@ -435,12 +435,12 @@ static void parse_em_data(struct seq_file *m)
>
> static void maxmem_data(struct seq_file *m)
> {
> - unsigned long maxmem = 0;
> + unsigned long long maxmem = 0;

What about using u64 instead, for readability ?

>
> - maxmem += drmem_info->n_lmbs * drmem_info->lmb_size;
> - maxmem += hugetlb_total_pages() * PAGE_SIZE;
> + maxmem += (unsigned long long)drmem_info->n_lmbs * (unsigned long long)drmem_info->lmb_size;

This line is likely too long. You only need to cast one of the two
operants to force a 64 bits multiply. And using u64 would shorten the line.

Can both multiplications overflow ?

Christophe

> + maxmem += (unsigned long long)hugetlb_total_pages() * (unsigned long long)PAGE_SIZE;
>
> - seq_printf(m, "MaxMem=%ld\n", maxmem);
> + seq_printf(m, "MaxMem=%llu\n", maxmem);
> }
>
> static int pseries_lparcfg_data(struct seq_file *m, void *v)
>

2020-01-15 14:31:54

by Michael Bringmann

Subject: Re: [PATCH] Fix display of Maximum Memory

On 1/14/20 11:41 PM, Christophe Leroy wrote:
>
>
> Le 14/01/2020 à 22:07, Michael Bringmann a écrit :
>> Correct overflow problem in calculation+display of Maximum Memory
>> value to syscfg where 32bits is insufficient.
>>
>> Signed-off-by: Michael Bringmann <[email protected]>
>> ---
>>   arch/powerpc/platforms/pseries/lparcfg.c | 8 ++++----
>>   1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/powerpc/platforms/pseries/lparcfg.c b/arch/powerpc/platforms/pseries/lparcfg.c
>> index 4ee2594..183aeb7 100644
>> --- a/arch/powerpc/platforms/pseries/lparcfg.c
>> +++ b/arch/powerpc/platforms/pseries/lparcfg.c
>> @@ -435,12 +435,12 @@ static void parse_em_data(struct seq_file *m)
>>
>>   static void maxmem_data(struct seq_file *m)
>>   {
>> -       unsigned long maxmem = 0;
>> +       unsigned long long maxmem = 0;
>
> What about using u64 instead, for readability ?

Okay.
>
>>
>> -       maxmem += drmem_info->n_lmbs * drmem_info->lmb_size;
>> -       maxmem += hugetlb_total_pages() * PAGE_SIZE;
>> +       maxmem += (unsigned long long)drmem_info->n_lmbs * (unsigned long long)drmem_info->lmb_size;
>
> This line is likely too long. You only need to cast one of the two operants to force a 64 bits multiply. And using u64 would shorten the line.
>
> Can both multiplications overflow ?

Yes.

>
> Christophe
>
>> +       maxmem += (unsigned long long)hugetlb_total_pages() * (unsigned long long)PAGE_SIZE;
>>
>> -       seq_printf(m, "MaxMem=%ld\n", maxmem);
>> +       seq_printf(m, "MaxMem=%llu\n", maxmem);
>>   }
>>
>>   static int pseries_lparcfg_data(struct seq_file *m, void *v)
>>
>

Thanks.
--
Michael W. Bringmann
Linux Technology Center
IBM Corporation
Tie-Line 363-5196
External: (512) 286-5196
Cell: (512) 466-0650
[email protected]