powerpc/fadump: set an upper limit for boot memory size From: Hari Bathini By default, 5% of system RAM is reserved for preserving boot memory. Alternatively, a user can specify the amount of memory to reserve. See Documentation/powerpc/firmware-assisted-dump.txt for details. In addition to the memory reserved for preserving boot memory, some more memory is reserved, to save HPTE region, CPU state data and ELF core headers. Memory Reservation during first kernel looks like below: Low memory Top of memory 0 boot memory size | | | |<--Reserved dump area -->| V V | Permanent Reservation V +-----------+----------/ /----------+---+----+-----------+----+ | | |CPU|HPTE| DUMP |ELF | +-----------+----------/ /----------+---+----+-----------+----+ | ^ | | \ / ------------------------------------------- Boot memory content gets transferred to reserved area by firmware at the time of crash The implicit rule here is that the sum of the sizes of boot memory, CPU state data, HPTE region and ELF core headers can't be greater than the total memory size. But currently, a user is allowed to specify any value as boot memory size. So, the above rule is violated when a boot memory size closer to 50% of the total available memory is specified. As the kernel is not handling this currently, it may lead to undefined behavior. Fix it by setting an upper limit for boot memory size to 25% of the total available memory. Signed-off-by: Hari Bathini --- arch/powerpc/include/asm/fadump.h | 3 +++ arch/powerpc/kernel/fadump.c | 15 ++++++++++++++- 2 files changed, 17 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/include/asm/fadump.h b/arch/powerpc/include/asm/fadump.h index 0031806..3d5e8ef 100644 --- a/arch/powerpc/include/asm/fadump.h +++ b/arch/powerpc/include/asm/fadump.h @@ -43,6 +43,9 @@ #define MIN_BOOT_MEM (((RMA_END < (0x1UL << 28)) ? (0x1UL << 28) : RMA_END) \ + (0x1UL << 26)) +/* The upper limit percentage for user specified boot memory size (25%) */ +#define MAX_BOOT_MEM_RATIO 4 + #define memblock_num_regions(memblock_type) (memblock.memblock_type.cnt) /* Firmware provided dump sections */ diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c index 8f0c7c5..e42e2c5 100644 --- a/arch/powerpc/kernel/fadump.c +++ b/arch/powerpc/kernel/fadump.c @@ -216,8 +216,21 @@ static inline unsigned long fadump_calculate_reserve_size(void) * Check if the size is specified through fadump_reserve_mem= cmdline * option. If yes, then use that. */ - if (fw_dump.reserve_bootvar) + if (fw_dump.reserve_bootvar) { + /* + * Adjust if the boot memory size specified is above + * the upper limit. + */ + if (fw_dump.reserve_bootvar > + (memblock_end_of_DRAM() / MAX_BOOT_MEM_RATIO)) { + fw_dump.reserve_bootvar = (memblock_end_of_DRAM() / + MAX_BOOT_MEM_RATIO); + pr_info("Adjusted boot memory size to %luMB\n", + (fw_dump.reserve_bootvar >> 20)); + } + return fw_dump.reserve_bootvar; + } /* divide by 20 to get 5% of value */ size = memblock_end_of_DRAM() / 20;