Hi Guo,
On Thu, Feb 10, 2022 at 4:14 PM Chuanhong Guo <gch981213@xxxxxxxxx> wrote:
>
> It's reported that current memory detection code occasionally detects
> larger memory under some bootloaders.
> Current memory detection code tests whether address space wraps around
> on KSEG0, which is unreliable because it's cached.
>
> Rewrite memory size detection to perform the same test on KSEG1 instead.
> While at it, this patch also does the following two things:
> 1. use a fixed pattern instead of a random function pointer as the magic
> value.
> 2. add an additional memory write and a second comparison as part of the
> test to prevent possible smaller memory detection result due to
> leftover values in memory.
>
> Fixes: 139c949f7f0a MIPS: ("ralink: mt7621: add memory detection support")
> Reported-by: Rui Salvaterra <rsalvaterra@xxxxxxxxx>
> Signed-off-by: Chuanhong Guo <gch981213@xxxxxxxxx>
> ---
> arch/mips/ralink/mt7621.c | 36 +++++++++++++++++++++++-------------
> 1 file changed, 23 insertions(+), 13 deletions(-)
>
> diff --git a/arch/mips/ralink/mt7621.c b/arch/mips/ralink/mt7621.c
> index d6efffd4dd20..12c8808e0dea 100644
> --- a/arch/mips/ralink/mt7621.c
> +++ b/arch/mips/ralink/mt7621.c
> @@ -22,7 +22,9 @@
>
> #include "common.h"
>
> -static void *detect_magic __initdata = detect_memory_region;
> +#define MT7621_MEM_TEST_PATTERN 0xaa5555aa
> +
> +static u32 detect_magic __initdata;
>
> int pcibios_root_bridge_prepare(struct pci_host_bridge *bridge)
> {
> @@ -58,24 +60,32 @@ phys_addr_t mips_cpc_default_phys_base(void)
> panic("Cannot detect cpc address");
> }
>
> +static bool __init mt7621_addr_wraparound_test(phys_addr_t size)
> +{
> + void *dm = (void *)KSEG1ADDR(&detect_magic);
> +
> + if (CPHYSADDR(dm + size) >= MT7621_LOWMEM_MAX_SIZE)
> + return true;
> + __raw_writel(MT7621_MEM_TEST_PATTERN, dm);
> + if (__raw_readl(dm) != __raw_readl(dm + size))
> + return false;
> + __raw_writel(!MT7621_MEM_TEST_PATTERN, dm);
> + return __raw_readl(dm) == __raw_readl(dm + size);
> +}
> +
> static void __init mt7621_memory_detect(void)
> {
> - void *dm = &detect_magic;
> phys_addr_t size;
>
> - for (size = 32 * SZ_1M; size < 256 * SZ_1M; size <<= 1) {
> - if (!__builtin_memcmp(dm, dm + size, sizeof(detect_magic)))
> - break;
> + for (size = 32 * SZ_1M; size <= 256 * SZ_1M; size <<= 1) {
> + if (mt7621_addr_wraparound_test(size)) {
> + memblock_add(MT7621_LOWMEM_BASE, size);
> + return;
> + }
> }
>
> - if ((size == 256 * SZ_1M) &&
> - (CPHYSADDR(dm + size) < MT7621_LOWMEM_MAX_SIZE) &&
> - __builtin_memcmp(dm, dm + size, sizeof(detect_magic))) {
> - memblock_add(MT7621_LOWMEM_BASE, MT7621_LOWMEM_MAX_SIZE);
> - memblock_add(MT7621_HIGHMEM_BASE, MT7621_HIGHMEM_SIZE);
> - } else {
> - memblock_add(MT7621_LOWMEM_BASE, size);
> - }
> + memblock_add(MT7621_LOWMEM_BASE, MT7621_LOWMEM_MAX_SIZE);
> + memblock_add(MT7621_HIGHMEM_BASE, MT7621_HIGHMEM_SIZE);
> }
>
> void __init ralink_of_remap(void)
> --
> 2.34.1
>
Thanks for your change. I think this will also fix
https://lore.kernel.org/lkml/202201191557.OISJHNMi-lkp@xxxxxxxxx/
since you are removing __builtin_memcmp usage.
Ilya
