RISC-V reserved memory problems
Alexandre Ghiti
alex at ghiti.fr
Thu Mar 9 04:31:24 PST 2023
On 3/9/23 11:30, Alexandre Ghiti wrote:
> Hi Conor,
>
> On 8/16/22 22:41, Conor.Dooley at microchip.com wrote:
>> Hey all,
>> We've run into a bit of a problem with reserved memory on PolarFire, or
>> more accurately a pair of problems that seem to have opposite fixes.
>>
>> The first of these problems is triggered when trying to implement a
>> remoteproc driver. To get the reserved memory buffer, remoteproc
>> does an of_reserved_mem_lookup(), something like:
>>
>> np = of_parse_phandle(pdev->of_node, "memory-region", 0);
>> if (!np)
>> return -EINVAL;
>>
>> rmem = of_reserved_mem_lookup(np);
>> if (!rmem)
>> return -EINVAL;
>>
>> of_reserved_mem_lookup() then uses reserved_mem[i].name to try and find
>> a match - but this was triggering kernel panics for us. We did some
>> debugging and found that the name string's pointer was pointing to an
>> address in the 0x4000_0000 range. The minimum reproduction for this
>
>
> 0x4000_0000 corresponds to DTB_EARLY_BASE_VA: this is the address that
> is used to map the dtb before we can access it using the linear mapping.
>
>
>> crash is attached - it hacks in some print_reserved_mem()s into
>> setup_vm_final() around a tlb flush so you can see the before/after.
>> (You'll need a reserved memory node in your dts to replicate)
>>
>> The output is like so, with the same crash as in the remoteproc driver:
>>
>> [ 0.000000] Linux version 6.0.0-rc1-00001-g0d9d6953d834
>> (conor at wendy) (riscv64-unknown-linux-gnu-gcc (g5964b5cd727) 11.1.0,
>> GNU ld (GNU Binutils) 2.37) #1 SMP Tue Aug 16 13:42:09 IST 2022
>> [ 0.000000] OF: fdt: Ignoring memory range 0x80000000 - 0x80200000
>> [ 0.000000] Machine model: Microchip PolarFire-SoC Icicle Kit
>> [ 0.000000] earlycon: ns16550a0 at MMIO32 0x0000000020100000
>> (options '115200n8')
>> [ 0.000000] printk: bootconsole [ns16550a0] enabled
>> [ 0.000000] printk: debug: skip boot console de-registration.
>> [ 0.000000] efi: UEFI not found.
>> [ 0.000000] before flush
>> [ 0.000000] OF: reserved mem: debug name is fabricbuf at ae000000
>> [ 0.000000] after flush
>> [ 0.000000] Unable to handle kernel paging request at virtual
>> address 00000000401c31ac
>
>
> You take the trap here because the mapping for the dtb does not exist
> in swapper_pg_dir, but you don't need this mapping anymore as you can
> access the device tree through the linear mapping now.
You can forget everything below, I was completely wrong. I'll follow up
on Mike's answer.
>
> I would say that: you build your kernel with CONFIG_BUILTIN_DTB and
> then you don't call early_init_dt_verify which resets
> initial_boot_params to the linear mapping address (it was initially
> set to 0x4000_0000 in parse_dtb). If that's the case, does the
> following fix your issue?
>
>
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index 376d2827e736..2b09f0bd8432 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -276,6 +276,7 @@ void __init setup_arch(char **cmdline_p)
> efi_init();
> paging_init();
> #if IS_ENABLED(CONFIG_BUILTIN_DTB)
> + initial_boot_params = __va(XIP_FIXUP(dtb_early_pa));
> unflatten_and_copy_device_tree();
> #else
> if (early_init_dt_verify(__va(XIP_FIXUP(dtb_early_pa))))
>
>
>> [ 0.000000] Oops [#1]
>> [ 0.000000] Modules linked in:
>> [ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted
>> 6.0.0-rc1-00001-g0d9d6953d834 #1
>> [ 0.000000] Hardware name: Microchip PolarFire-SoC Icicle Kit (DT)
>> [ 0.000000] epc : string+0x4a/0xea
>> [ 0.000000] ra : vsnprintf+0x1e4/0x336
>> [ 0.000000] epc : ffffffff80335ea0 ra : ffffffff80338936 sp :
>> ffffffff81203be0
>> [ 0.000000] gp : ffffffff812e0a98 tp : ffffffff8120de40 t0 :
>> 0000000000000000
>> [ 0.000000] t1 : ffffffff81203e28 t2 : 7265736572203a46 s0 :
>> ffffffff81203c20
>> [ 0.000000] s1 : ffffffff81203e28 a0 : ffffffff81203d22 a1 :
>> 0000000000000000
>> [ 0.000000] a2 : ffffffff81203d08 a3 : 0000000081203d21 a4 :
>> ffffffffffffffff
>> [ 0.000000] a5 : 00000000401c31ac a6 : ffff0a00ffffff04 a7 :
>> ffffffffffffffff
>> [ 0.000000] s2 : ffffffff81203d08 s3 : ffffffff81203d00 s4 :
>> 0000000000000008
>> [ 0.000000] s5 : ffffffff000000ff s6 : 0000000000ffffff s7 :
>> 00000000ffffff00
>> [ 0.000000] s8 : ffffffff80d9821a s9 : ffffffff81203d22 s10:
>> 0000000000000002
>> [ 0.000000] s11: ffffffff80d9821c t3 : ffffffff812f3617 t4 :
>> ffffffff812f3617
>> [ 0.000000] t5 : ffffffff812f3618 t6 : ffffffff81203d08
>> [ 0.000000] status: 0000000200000100 badaddr: 00000000401c31ac
>> cause: 000000000000000d
>> [ 0.000000] [<ffffffff80338936>] vsnprintf+0x1e4/0x336
>> [ 0.000000] [<ffffffff80055ae2>] vprintk_store+0xf6/0x344
>> [ 0.000000] [<ffffffff80055d86>] vprintk_emit+0x56/0x192
>> [ 0.000000] [<ffffffff80055ed8>] vprintk_default+0x16/0x1e
>> [ 0.000000] [<ffffffff800563d2>] vprintk+0x72/0x80
>> [ 0.000000] [<ffffffff806813b2>] _printk+0x36/0x50
>> [ 0.000000] [<ffffffff8068af48>] print_reserved_mem+0x1c/0x24
>> [ 0.000000] [<ffffffff808057ec>] paging_init+0x528/0x5bc
>> [ 0.000000] [<ffffffff808031ae>] setup_arch+0xd0/0x592
>> [ 0.000000] [<ffffffff8080070e>] start_kernel+0x82/0x73c
>> [ 0.000000] ---[ end trace 0000000000000000 ]---
>> [ 0.000000] Kernel panic - not syncing: Attempted to kill the idle
>> task!
>> [ 0.000000] ---[ end Kernel panic - not syncing: Attempted to kill
>> the idle task! ]---
>>
>> We traced this back to early_init_fdt_scan_reserved_mem() in
>> setup_bootmem() - moving it later back up the boot sequence to
>> after the dt has been remapped etc has fixed the problem for us.
>>
>> The least movement to get it working is attached, and also pushed
>> here: git.kernel.org/conor/c/1735589baefc
>>
>> The second problem is a bit more complicated to explain - but we
>> found the solution conflicted with the remoteproc fix as we had
>> to move early_init_fdt_scan_reserved_mem() _earlier_ in the boot
>> process to solve this one.
>>
>> We want to have a node in our devicetree that contains some memory
>> that is non-cached & marked as reserved-memory. Maybe we have just
>> missed something, but from what we've seen:
>> - the really early setup looks at the dtb, picks the highest bit
>> of memory and puts the dtb etc there so it can start using it
>> - early_init_fdt_scan_reserved_mem() is then called, which figures
>> out if memory is reserved or not.
>>
>> Unfortunately, the highest bit of memory is the non-cached bit so
>> everything falls over, but we can avoid this by moving the call to
>> early_init_fdt_scan_reserved_mem() above the dtb memblock alloc that
>> takes place right before it in setup_bootmem().
>
>
> And then I suppose the allocations you are mentioning happen in
> unflatten_XXX, so parsing the device tree for reserved memory nodes
> before this should do the trick. Does the following fix your second
> issue?
>
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index 2b09f0bd8432..94b3d049fe9d 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -277,14 +277,15 @@ void __init setup_arch(char **cmdline_p)
> paging_init();
> #if IS_ENABLED(CONFIG_BUILTIN_DTB)
> initial_boot_params = __va(XIP_FIXUP(dtb_early_pa));
> + early_init_fdt_scan_reserved_mem();
> unflatten_and_copy_device_tree();
> #else
> - if (early_init_dt_verify(__va(XIP_FIXUP(dtb_early_pa))))
> + if (early_init_dt_verify(__va(XIP_FIXUP(dtb_early_pa)))) {
> + early_init_fdt_scan_reserved_mem();
> unflatten_device_tree();
> - else
> + } else
> pr_err("No DTB found in kernel mappings\n");
> #endif
> - early_init_fdt_scan_reserved_mem();
> misc_mem_init();
>
> init_resources();
>
>
>
>>
>> Obviously, both of these changes are moving the function call in
>> opposite directions and we can only really do one of them. We are not
>> sure if what we are doing with the non-cached reserved-memory section
>> is just not permitted & cannot work - or if this is something that
>> was overlooked for RISC-V specifically and works for other archs.
>>
>> It does seem like the first issue is a real bug, and I am happy to
>> submit the patch for that whenever - but having two problems with
>> opposite fixes seemed as if there was something else lurking that we
>> just don't have enough understanding to detect.
>>
>> Any help would be great!
>>
>> Thanks,
>> Conor.
>>
>
> Even if that does not fix your issue, the first patch is necessary as
> it fixes initial_boot_params.
>
>
>>
>>
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