RISC-V reserved memory problems

Thu Aug 18 07:32:09 PDT 2022

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
> 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
> [    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().
> 
> 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.
> 
> 
> 

Hello Conor,

could you, please, provide the relevant device-tree sniplets.

Please, have a look at the no-map property in
Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt. 
It controls if the kernel in any way will access the memory outside of 
your new driver.

Best regards

Heinrich