Re: [PATCH] Fix display of Maximum Memory

From: Christophe Leroy
Date: Wed Jan 15 2020 - 00:41:39 EST




Le 14/01/2020 Ã 22:07, Michael Bringmann a ÃcritÂ:
Correct overflow problem in calculation+display of Maximum Memory
value to syscfg where 32bits is insufficient.

Signed-off-by: Michael Bringmann <mwb@xxxxxxxxxxxxx>
---
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)