Messages in this thread | | | Date | Thu, 18 Aug 2022 16:32:09 +0200 | Subject | Re: RISC-V reserved memory problems | From | Heinrich Schuchardt <> |
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On 8/16/22 22:41, Conor.Dooley@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@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@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
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