Re: [PATCH V5 4/6] RISC-V: Fixup getting correct current pc

[Conor.Dooley]

On 09/08/2022 22:13, Conor.Dooley@xxxxxxxxxxxxx wrote:
> On 02/08/2022 13:18, Xianting Tian wrote:
>> When use 'echo c > /proc/sysrq-trigger' to trigger kdump, riscv_crash_save_regs()
>> will be called to save regs to vmcore, we found "epc" value 00ffffffa5537400
>> is not a valid kernel virtual address, but is a user virtual address. Other
>> regs(eg, ra, sp, gp...) are correct kernel virtual address.
>> Actually 0x00ffffffb0dd9400 is the user mode PC of 'PID: 113 Comm: sh', which
>> is saved in the task's stack.
>>
>> [   21.201701] CPU: 0 PID: 113 Comm: sh Kdump: loaded Not tainted 5.18.9 #45
>> [   21.201979] Hardware name: riscv-virtio,qemu (DT)
>> [   21.202160] epc : 00ffffffa5537400 ra : ffffffff80088640 sp : ff20000010333b90
>> [   21.202435]  gp : ffffffff810dde38 tp : ff6000000226c200 t0 : ffffffff8032be7c
>> [   21.202707]  t1 : 0720072007200720 t2 : 30203a7375746174 s0 : ff20000010333cf0
>> [   21.202973]  s1 : 0000000000000000 a0 : ff20000010333b98 a1 : 0000000000000001
>> [   21.203243]  a2 : 0000000000000010 a3 : 0000000000000000 a4 : 28c8f0aeffea4e00
>> [   21.203519]  a5 : 28c8f0aeffea4e00 a6 : 0000000000000009 a7 : ffffffff8035c9b8
>> [   21.203794]  s2 : ffffffff810df0a8 s3 : ffffffff810df718 s4 : ff20000010333b98
>> [   21.204062]  s5 : 0000000000000000 s6 : 0000000000000007 s7 : ffffffff80c4a468
>> [   21.204331]  s8 : 00ffffffef451410 s9 : 0000000000000007 s10: 00aaaaaac0510700
>> [   21.204606]  s11: 0000000000000001 t3 : ff60000001218f00 t4 : ff60000001218f00
>> [   21.204876]  t5 : ff60000001218000 t6 : ff200000103338b8
>> [   21.205079] status: 0000000200000020 badaddr: 0000000000000000 cause: 0000000000000008
>>
>> With the incorrect PC, the backtrace showed by crash tool as below, the first
>> stack frame is abnormal,
>>
>> crash> bt
>> PID: 113      TASK: ff60000002269600  CPU: 0    COMMAND: "sh"
>>  #0 [ff2000001039bb90] __efistub_.Ldebug_info0 at 00ffffffa5537400 <-- Abnormal
>>  #1 [ff2000001039bcf0] panic at ffffffff806578ba
>>  #2 [ff2000001039bd50] sysrq_reset_seq_param_set at ffffffff8038c030
>>  #3 [ff2000001039bda0] __handle_sysrq at ffffffff8038c5f8
>>  #4 [ff2000001039be00] write_sysrq_trigger at ffffffff8038cad8
>>  #5 [ff2000001039be20] proc_reg_write at ffffffff801b7edc
>>  #6 [ff2000001039be40] vfs_write at ffffffff80152ba6
>>  #7 [ff2000001039be80] ksys_write at ffffffff80152ece
>>  #8 [ff2000001039bed0] sys_write at ffffffff80152f46
>>
>> With the patch, we can get current kernel mode PC, the output as below,
>>
>> [   17.607658] CPU: 0 PID: 113 Comm: sh Kdump: loaded Not tainted 5.18.9 #42
>> [   17.607937] Hardware name: riscv-virtio,qemu (DT)
>> [   17.608150] epc : ffffffff800078f8 ra : ffffffff8008862c sp : ff20000010333b90
>> [   17.608441]  gp : ffffffff810dde38 tp : ff6000000226c200 t0 : ffffffff8032be68
>> [   17.608741]  t1 : 0720072007200720 t2 : 666666666666663c s0 : ff20000010333cf0
>> [   17.609025]  s1 : 0000000000000000 a0 : ff20000010333b98 a1 : 0000000000000001
>> [   17.609320]  a2 : 0000000000000010 a3 : 0000000000000000 a4 : 0000000000000000
>> [   17.609601]  a5 : ff60000001c78000 a6 : 000000000000003c a7 : ffffffff8035c9a4
>> [   17.609894]  s2 : ffffffff810df0a8 s3 : ffffffff810df718 s4 : ff20000010333b98
>> [   17.610186]  s5 : 0000000000000000 s6 : 0000000000000007 s7 : ffffffff80c4a468
>> [   17.610469]  s8 : 00ffffffca281410 s9 : 0000000000000007 s10: 00aaaaaab5bb6700
>> [   17.610755]  s11: 0000000000000001 t3 : ff60000001218f00 t4 : ff60000001218f00
>> [   17.611041]  t5 : ff60000001218000 t6 : ff20000010333988
>> [   17.611255] status: 0000000200000020 badaddr: 0000000000000000 cause: 0000000000000008
>>
>> With the correct PC, the backtrace showed by crash tool as below,
>>
>> crash> bt
>> PID: 113      TASK: ff6000000226c200  CPU: 0    COMMAND: "sh"
>>  #0 [ff20000010333b90] riscv_crash_save_regs at ffffffff800078f8 <--- Normal
>>  #1 [ff20000010333cf0] panic at ffffffff806578c6
>>  #2 [ff20000010333d50] sysrq_reset_seq_param_set at ffffffff8038c03c
>>  #3 [ff20000010333da0] __handle_sysrq at ffffffff8038c604
>>  #4 [ff20000010333e00] write_sysrq_trigger at ffffffff8038cae4
>>  #5 [ff20000010333e20] proc_reg_write at ffffffff801b7ee8
>>  #6 [ff20000010333e40] vfs_write at ffffffff80152bb2
>>  #7 [ff20000010333e80] ksys_write at ffffffff80152eda
>>  #8 [ff20000010333ed0] sys_write at ffffffff80152f52
>>
>> Fixes: e53d28180d4d ("RISC-V: Add kdump support")
> 
> This patch is also a fix, but not at the start of the series which
> (I think) makes it less likely to be picked up for an auto-backport.
> 
> As it doesn't seem to depend on the prior patches, can you move this
> up to 2/6 in the series?
> 

Plus, it'd be nice if the subject gave some more sub component context
& the same applies to most of the patches in the series.