Re: [PATCH v2] riscv: Fix memblock reservation for device tree blob

[Bin Meng]

On Sat, Sep 28, 2019 at 7:14 AM Albert Ou <aou@xxxxxxxxxxxxxxxxx> wrote:
>
> This fixes an error with how the FDT blob is reserved in memblock.
> An incorrect physical address calculation exposed the FDT header to
> unintended corruption, which typically manifested with of_fdt_raw_init()
> faulting during late boot after fdt_totalsize() returned a wrong value.
> Systems with smaller physical memory sizes more frequently trigger this
> issue, as the kernel is more likely to allocate from the DMA32 zone
> where bbl places the DTB after the kernel image.
>
> Commit 671f9a3e2e24 ("RISC-V: Setup initial page tables in two stages")
> changed the mapping of the DTB to reside in the fixmap area.
> Consequently, early_init_fdt_reserve_self() cannot be used anymore in
> setup_bootmem() since it relies on __pa() to derive a physical address,
> which does not work with dtb_early_va that is no longer a valid kernel
> logical address.
>
> The reserved[0x1] region shows the effect of the pointer underflow
> resulting from the __pa(initial_boot_params) offset subtraction:
>
> [    0.000000] MEMBLOCK configuration:
> [    0.000000]  memory size = 0x000000001fe00000 reserved size = 0x0000000000a2e514
> [    0.000000]  memory.cnt  = 0x1
> [    0.000000]  memory[0x0]     [0x0000000080200000-0x000000009fffffff], 0x000000001fe00000 bytes flags: 0x0
> [    0.000000]  reserved.cnt  = 0x2
> [    0.000000]  reserved[0x0]   [0x0000000080200000-0x0000000080c2dfeb], 0x0000000000a2dfec bytes flags: 0x0
> [    0.000000]  reserved[0x1]   [0xfffffff080100000-0xfffffff080100527], 0x0000000000000528 bytes flags: 0x0
>
> With the fix applied:
>
> [    0.000000] MEMBLOCK configuration:
> [    0.000000]  memory size = 0x000000001fe00000 reserved size = 0x0000000000a2e514
> [    0.000000]  memory.cnt  = 0x1
> [    0.000000]  memory[0x0]     [0x0000000080200000-0x000000009fffffff], 0x000000001fe00000 bytes flags: 0x0
> [    0.000000]  reserved.cnt  = 0x2
> [    0.000000]  reserved[0x0]   [0x0000000080200000-0x0000000080c2dfeb], 0x0000000000a2dfec bytes flags: 0x0
> [    0.000000]  reserved[0x1]   [0x0000000080e00000-0x0000000080e00527], 0x0000000000000528 bytes flags: 0x0
>
> Fixes: 671f9a3e2e24 ("RISC-V: Setup initial page tables in two stages")

I also found that with commit 671f9a3e2e24 ("RISC-V: Setup initial
page tables in two stages"), when booting the kernel from U-Boot via:

=> bootm $kernel_addr_t - $fdtcontroladdr
($kernel_addr_t = 0x84000000 and $fdtcontroladdr = 0xff741c60)

kernel does not boot. I looked at people's instructions of booting
Linux kernel, and they seem to have such:

=> cp.l ${fdtcontroladdr} ${fdt_addr_r} 0x10000
=> bootm ${kernel_addr_r} - ${fdt_addr_r}

where ${fdt_addr_r} is 0x88000000, and "bootm 84000000  - 88000000"
can make the kernel boot.

Thanks for the patch. Now "bootm $kernel_addr_t - $fdtcontroladdr" works again!

Tested-by: Bin Meng <bmeng.cn@xxxxxxxxx>

> Signed-off-by: Albert Ou <aou@xxxxxxxxxxxxxxxxx>
> ---
>
> Changes in v2:
> * Changed variable identifier to dtb_early_pa per reviewer feedback.
> * Removed whitespace change.
>
>  arch/riscv/mm/init.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>

Regards,
Bin