Re: [PATCH v1 3/4] powerpc/code-patching: Use jump_label for testing freed initmem
From: Christophe Leroy <hidden>
Date: 2022-05-19 17:29:55
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Le 19/05/2022 à 08:53, Christophe Leroy a écrit :
Le 19/05/2022 à 08:27, Christophe Leroy a écrit :quoted
Le 19/05/2022 à 04:17, Guenter Roeck a écrit :quoted
On Tue, Mar 22, 2022 at 04:40:20PM +0100, Christophe Leroy wrote:quoted
Once init is done, initmem is freed forever so no need to test system_state at every call to patch_instruction(). Use jump_label. This reduces by 2% the time needed to activate ftrace on an 8xx.It also causes the qemu mpc8544ds emulation to crash. BUG: Unable to handle kernel data access on write at 0xc122eb34 Faulting instruction address: 0xc001b580 Oops: Kernel access of bad area, sig: 11 [#1] BE PAGE_SIZE=4K MPC8544 DS Modules linked in: CPU: 0 PID: 1 Comm: swapper Not tainted 5.18.0-rc7-next-20220518 #1 NIP: c001b580 LR: c001b560 CTR: 00000003 REGS: c5107dd0 TRAP: 0300 Not tainted (5.18.0-rc7-next-20220518) MSR: 00009000 <EE,ME> CR: 24000882 XER: 00000000 DEAR: c122eb34 ESR: 00800000 GPR00: c001b560 c5107ec0 c5120020 10000000 00000000 00000078 0c000000 cfffffff GPR08: c001e9ec 00000001 00000007 00000000 44000882 00000000 c0005178 00000000 GPR16: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 GPR24: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 c1230000 NIP [c001b580] free_initmem+0x48/0xa8 LR [c001b560] free_initmem+0x28/0xa8 Call Trace: [c5107ec0] [c001b560] free_initmem+0x28/0xa8 (unreliable) [c5107ee0] [c00051b0] kernel_init+0x38/0x150 [c5107f00] [c001626c] ret_from_kernel_thread+0x5c/0x64 Instruction dump: 3fe0c123 912a00dc 90010024 48000665 3d20c218 8929fa65 2c090000 41820058 813feb34 2c090000 4082003c 39200001 <913feb34> 80010024 3cc0c114 83e1001c Reverting this patch fixes the problem.That's strange. I was able to reproduce the problem. Removing the __ro_after_init in front of DEFINE_STATIC_KEY_FALSE(init_mem_is_free) fixes the problem. I can't understand why, mark_readonly() is called after free_initmem().Moving static_branch_enable(&init_mem_is_free) before mark_initmem_nx() also solves the problem. There must be something wrong with mark_initmem_nx().
Fixing patch sent, see https://patchwork.ozlabs.org/project/linuxppc-dev/patch/2e35f0fd649c83c5add17a99514ac040767be93a.1652981047.git.christophe.leroy@csgroup.eu/ Christophe