On 20/05/26 14:30, Christophe Leroy (CS GROUP) wrote:

Le 20/05/2026 à 07:53, Sayali Patil a écrit :

quoted

The MIN_RMA size checks in fadump_setup_param_area() use
(MIN_RMA * 1024 * 1024), which is evaluated in int and can
overflow when MIN_RMA is 2048 or larger. This triggers compiler
warnings such as:

warning: integer overflow in expression of type 'int'
results in '0' [-Woverflow]

Promote MIN_RMA to u64 before the multiplication so the expression
is evaluated in 64-bit and matches the surrounding physical address
and memory size calculations.

This fixes both the comparison against ppc64_rma_size and the
assignment to range_start.

How do you create that problem ? MIN_RMA has a fixed value of 768 which 
is defined in asm/prom.h

Agreed, MIN_RMA is currently fixed at 768MB.
While going through the code, I thought this could become a
problem if MIN_RMA is increased beyond values such as SZ_2G.

quoted

Fixes: b7bb46062457 ("powerpc/fadump: fix additional param memory 
reservation for HASH MMU")
Signed-off-by: Sayali Patil <redacted>
---
  arch/powerpc/kernel/fadump.c | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
index 501d43bf18f3..dea7f7105e42 100644
--- a/arch/powerpc/kernel/fadump.c
+++ b/arch/powerpc/kernel/fadump.c

@@ -1759,10 +1759,10 @@ void __init fadump_setup_param_area(void)

           * 2. The range should be between MIN_RMA and RMA size 
(ppc64_rma_size)
           * 3. It must not overlap with the fadump reserved area.
           */
-        if (ppc64_rma_size < MIN_RMA*1024*1024)
+        if (ppc64_rma_size < (u64)MIN_RMA * 1024 * 1024)

As you are modifying that line, please use SZ_1M instead of keeping 
opencoded 1024 * 1024.

quoted

              return;
-        range_start = MIN_RMA * 1024 * 1024;
+        range_start = (u64)MIN_RMA * 1024 * 1024;

Same.

quoted

          range_end = min(ppc64_rma_size, fw_dump.boot_mem_top);
      }

Maybe the best would be to define MIN_RMA as a bytes value in asm/prom.h 
and to divide the value by SZ_1M in kernel/prom_init.c when initialising 
ibm_architecture_vec_template.

That way you could just define it as SZ_2G instead of the problematic 
2048 you mention.

Thanks for the review Christophe!
I will incorporate all the suggested improvements in v2.

Regards,
Sayali