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Re: [PATCH] hw/arm/boot: set initrd parameters to 64bit in fdt


From: Schspa Shi
Subject: Re: [PATCH] hw/arm/boot: set initrd parameters to 64bit in fdt
Date: Tue, 8 Nov 2022 20:52:22 +0800

Alex Bennée <alex.bennee@linaro.org> writes:

> Schspa Shi <schspa@gmail.com> writes:
>
>> We use 32bit value for linux,initrd-[start/end], when we have
>> loader_start > 4GB, there will be a wrong initrd_start passed
>> to the kernel, and the kernel will report the following warning.
>>
>> [    0.000000] ------------[ cut here ]------------
>> [    0.000000] initrd not fully accessible via the linear mapping -- please 
>> check your bootloader ...
>> [    0.000000] WARNING: CPU: 0 PID: 0 at arch/arm64/mm/init.c:355 
>> arm64_memblock_init+0x158/0x244
>> [    0.000000] Modules linked in:
>> [    0.000000] CPU: 0 PID: 0 Comm: swapper Tainted: G        W          
>> 6.1.0-rc3-13250-g30a0b95b1335-dirty #28
>> [    0.000000] Hardware name: Horizon Sigi Virtual development board
>> (DT)
>
> Is this an out-of-tree board model?
>

Yes, this is a virtual board created by myself.

>> [    0.000000] pstate: 600000c5 (nZCv daIF -PAN -UAO -TCO -DIT -SSBS 
>> BTYPE=--)
>> [    0.000000] pc : arm64_memblock_init+0x158/0x244
>> [    0.000000] lr : arm64_memblock_init+0x158/0x244
>> [    0.000000] sp : ffff800009273df0
>> [    0.000000] x29: ffff800009273df0 x28: 0000001000cc0010 x27: 
>> 0000800000000000
>> [    0.000000] x26: 000000000050a3e2 x25: ffff800008b46000 x24: 
>> ffff800008b46000
>> [    0.000000] x23: ffff800008a53000 x22: ffff800009420000 x21: 
>> ffff800008a53000
>> [    0.000000] x20: 0000000004000000 x19: 0000000004000000 x18: 
>> 00000000ffff1020
>> [    0.000000] x17: 6568632065736165 x16: 6c70202d2d20676e x15: 
>> 697070616d207261
>> [    0.000000] x14: 656e696c20656874 x13: 0a2e2e2e20726564 x12: 
>> 0000000000000000
>> [    0.000000] x11: 0000000000000000 x10: 00000000ffffffff x9 : 
>> 0000000000000000
>> [    0.000000] x8 : 0000000000000000 x7 : 796c6c756620746f x6 : 
>> 6e20647274696e69
>> [    0.000000] x5 : ffff8000093c7c47 x4 : ffff800008a2102f x3 : 
>> ffff800009273a88
>> [    0.000000] x2 : 80000000fffff038 x1 : 00000000000000c0 x0 : 
>> 0000000000000056
>> [    0.000000] Call trace:
>> [    0.000000]  arm64_memblock_init+0x158/0x244
>> [    0.000000]  setup_arch+0x164/0x1cc
>> [    0.000000]  start_kernel+0x94/0x4ac
>> [    0.000000]  __primary_switched+0xb4/0xbc
>> [    0.000000] ---[ end trace 0000000000000000 ]---
>> [    0.000000] Zone ranges:
>> [    0.000000]   DMA      [mem 0x0000001000000000-0x0000001007ffffff]
>>
>> To fix it, we can change it to u64 type.
>>
>> Signed-off-by: Schspa Shi <schspa@gmail.com>
>> ---
>>  hw/arm/boot.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/hw/arm/boot.c b/hw/arm/boot.c
>> index 57efb61ee419..da719a4f8874 100644
>> --- a/hw/arm/boot.c
>> +++ b/hw/arm/boot.c
>> @@ -638,14 +638,14 @@ int arm_load_dtb(hwaddr addr, const struct 
>> arm_boot_info *binfo,
>>      }
>>
>>      if (binfo->initrd_size) {
>> -        rc = qemu_fdt_setprop_cell(fdt, "/chosen", "linux,initrd-start",
>> +        rc = qemu_fdt_setprop_u64(fdt, "/chosen", "linux,initrd-start",
>>                                     binfo->initrd_start);
>>          if (rc < 0) {
>>              fprintf(stderr, "couldn't set /chosen/linux,initrd-start\n");
>>              goto fail;
>>          }
>>
>> -        rc = qemu_fdt_setprop_cell(fdt, "/chosen", "linux,initrd-end",
>> +        rc = qemu_fdt_setprop_u64(fdt, "/chosen", "linux,initrd-end",
>>                                     binfo->initrd_start + 
>> binfo->initrd_size);
>>          if (rc < 0) {
>>              fprintf(stderr, "couldn't set /chosen/linux,initrd-end\n");
>
> On the face of things this seems fine because unlike the other linux
> properties they are not specified to be "expressed in #address-cells and
> #size-cells" but I do wonder how we got into the situation where the
> kernel and initrd ended up so high in the physical address space.
>

The reason why I faced this problem is there is no DRAM region below
4GB on the hardware. And I make this virtual board to have the same
memory layout as the hardware.

Although there is no something like #address-cells and #size-cells,
but Linux will handle the size correctly by calling the following code:

prop = of_get_flat_dt_prop(node, "linux,initrd-start", &len);

Please check the link at
Link: https://lore.kernel.org/all/20091105074724.10460.4083.stgit@angua/
Every Linux version support fdt on arm[64] platform should work without
problems.

> There is a whole comment in boot.c talking about keeping initrd within
> lowmem:
>
>     /*
>      * We want to put the initrd far enough into RAM that when the
>      * kernel is uncompressed it will not clobber the initrd. However
>      * on boards without much RAM we must ensure that we still leave
>      * enough room for a decent sized initrd, and on boards with large
>      * amounts of RAM we must avoid the initrd being so far up in RAM
>      * that it is outside lowmem and inaccessible to the kernel.
>      * So for boards with less  than 256MB of RAM we put the initrd
>      * halfway into RAM, and for boards with 256MB of RAM or more we put
>      * the initrd at 128MB.
>      * We also refuse to put the initrd somewhere that will definitely
>      * overlay the kernel we just loaded, though for kernel formats which
>      * don't tell us their exact size (eg self-decompressing 32-bit kernels)
>      * we might still make a bad choice here.
>      */
>

I think this lowmem does not mean below 4GB. and it is to make sure
the initrd_start > memblock_start_of_DRAM for Linux address range check.

> Is this just because the base RAM address of the board is outside of the
> 32 bit address range?

Yes, it is.


--
BRs
Schspa Shi



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