Hi Qian, On Fri, Oct 09, 2020 at 09:51:15AM +0100, Will Deacon wrote: > On Thu, Oct 08, 2020 at 09:18:24PM -0400, Qian Cai wrote: > > On Mon, 2020-10-05 at 17:43 +0100, Mark Rutland wrote: > > > The current initialization of the per-cpu offset register is difficult > > > to follow and this initialization is not always early enough for > > > upcoming instrumentation with KCSAN, where the instrumentation callbacks > > > use the per-cpu offset. > > > > > > To make it possible to support KCSAN, and to simplify reasoning about > > > early bringup code, let's initialize the per-cpu offset earlier, before > > > we run any C code that may consume it. To do so, this patch adds a new > > > init_this_cpu_offset() helper that's called before the usual > > > primary/secondary start functions. For consistency, this is also used to > > > re-initialize the per-cpu offset after the runtime per-cpu areas have > > > been allocated (which can change CPU0's offset). > > > > > > So that init_this_cpu_offset() isn't subject to any instrumentation that > > > might consume the per-cpu offset, it is marked with noinstr, preventing > > > instrumentation. > > > > > > Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx> > > > Cc: Catalin Marinas <catalin.marinas@xxxxxxx> > > > Cc: James Morse <james.morse@xxxxxxx> > > > Cc: Will Deacon <will@xxxxxxxxxx> > > > > Reverting this commit on the top of today's linux-next fixed an issue that > > Thunder X2 is unable to boot: > > > > .config: https://gitlab.com/cailca/linux-mm/-/blob/master/arm64.config Sorry about this. :/ Will, to save you reading all the below, I think the right thing to do for now is to revert this. Building with that config, I see a boot time-hang on the primary CPU under QEMU TCG, with or without VHE (in both cases, a stuck in a recursive synchronous exception). With the patch reverted, the kernel boots. Looking at the assembly, task_cpu() gets instrumented (which puts this patch on dodgy ground generally and I think warrants the revert), but as it's instrumented with KASAN_INLINE that doesn't immediately explain the issue since the shadow should be up and so we shouldn't call the report function. I'll dig into this some more. Assembly dumps below; for init_this_cpu_offset the reference to page_wait_table+0x4d00 is generating the address for __per_cpu_offset, but objdump doesn't have enough info to resolve that nicely. | ffffa00011143bc0 <init_this_cpu_offset>: | ffffa00011143bc0: a9bf7bfd stp x29, x30, [sp, #-16]! | ffffa00011143bc4: d5384100 mrs x0, sp_el0 | ffffa00011143bc8: 910003fd mov x29, sp | ffffa00011143bcc: 97bb29b9 bl ffffa0001000e2b0 <task_cpu> | ffffa00011143bd0: f0004ea1 adrp x1, ffffa00011b1a000 <page_wait_table+0x4d00> | ffffa00011143bd4: 913c6021 add x1, x1, #0xf18 | ffffa00011143bd8: f8605820 ldr x0, [x1, w0, uxtw #3] | ffffa00011143bdc: 97bb29b1 bl ffffa0001000e2a0 <set_my_cpu_offset> | ffffa00011143be0: a8c17bfd ldp x29, x30, [sp], #16 | ffffa00011143be4: d65f03c0 ret | ffffa0001000e2b0 <task_cpu>: | ffffa0001000e2b0: a9be7bfd stp x29, x30, [sp, #-32]! | ffffa0001000e2b4: d2d40001 mov x1, #0xa00000000000 // #175921860444160 | ffffa0001000e2b8: f2fbffe1 movk x1, #0xdfff, lsl #48 | ffffa0001000e2bc: 910003fd mov x29, sp | ffffa0001000e2c0: f9000bf3 str x19, [sp, #16] | ffffa0001000e2c4: aa0003f3 mov x19, x0 | ffffa0001000e2c8: 91012000 add x0, x0, #0x48 | ffffa0001000e2cc: 52800062 mov w2, #0x3 // #3 | ffffa0001000e2d0: d343fc03 lsr x3, x0, #3 | ffffa0001000e2d4: 38e16861 ldrsb w1, [x3, x1] | ffffa0001000e2d8: 7100003f cmp w1, #0x0 | ffffa0001000e2dc: 7a411041 ccmp w2, w1, #0x1, ne // ne = any | ffffa0001000e2e0: 540000aa b.ge ffffa0001000e2f4 <task_cpu+0x44> // b.tcont | ffffa0001000e2e4: b9404a60 ldr w0, [x19, #72] | ffffa0001000e2e8: f9400bf3 ldr x19, [sp, #16] | ffffa0001000e2ec: a8c27bfd ldp x29, x30, [sp], #32 | ffffa0001000e2f0: d65f03c0 ret | ffffa0001000e2f4: 9415af1f bl ffffa00010579f70 <__asan_report_load4_noabort> | ffffa0001000e2f8: 17fffffb b ffffa0001000e2e4 <task_cpu+0x34> | ffffa0001000e2fc: d503201f nop | ffffa0001000e2a0 <set_my_cpu_offset>: | ffffa0001000e2a0: d518d080 msr tpidr_el1, x0 | ffffa0001000e2a4: d65f03c0 ret | ffffa0001000e2a8: d503201f nop | ffffa0001000e2ac: d503201f nop Thanks, Mark.
