Re: [fedora-arm] Fwd: dummy_flush_tlb_a15_erratum in check_and_switch_context

-- Sent from my iPad On Jun 28, 2013, at 1:41, Peter Robinson pbrobinson@gmail.com wrote: > On Fri, Jun 28, 2013 at 5:09 AM, Jon Masters jonathan@jonmasters.org wrote: >> >> >> >> -------- Original Message -------- >> Subject: dummy_flush_tlb_a15_erratum in check_and_switch_context >> Date: Thu, 27 Jun 2013 23:48:14 -0400 >> From: Jon Masters jonathan@jonmasters.org >> Organization: World Organi{s,z}ation of Broken Dreams >> To: linux-arm-kernel@lists.infradead.org >> >> Hi Folks, >> >> Post mostly for Google's benefit. Fedora folks were reporting the >> following backtrace on Cortex-A8 OMAP: >> >> [ 12.182873] Internal error: Oops - undefined instruction: 0 [#1] SMP ARM >> [ 12.189971] Modules linked in: drm_kms_helper drm >> [ 12.194965] CPU: 0 PID: 153 Comm: dracut-initqueu Not tainted >> 3.10.0-0.rc7.git0.2.fc20.armv7hl #1 >> [ 12.204317] task: c9ee9b80 ti: c9f50000 task.ti: c9f50000 >> [ 12.210025] PC is at check_and_switch_context+0x3c0/0x44c >> [ 12.215724] LR is at check_and_switch_context+0x364/0x44c >> [ 12.221424] pc : [<c001dbd4>] lr : [<c001db78>] psr: 400f0093 >> [ 12.221424] sp : c9f51e40 ip : 00000000 fp : c9ebe860 >> [ 12.233532] r10: c08cb470 r9 : c08d97c8 r8 : c9ebe700 >> [ 12.239044] r7 : 00000000 r6 : 00000200 r5 : 00000000 r4 : 00000201 >> [ 12.245929] r3 : 00000000 r2 : 00000000 r1 : 00000000 r0 : 00000001 >> [ 12.252817] Flags: nZcv IRQs off FIQs on Mode SVC_32 ISA ARM >> Segment user >> [ 12.260436] Control: 10c5387d Table: 80004019 DAC: 00000015 >> [ 12.266497] Process dracut-initqueu (pid: 153, stack limit = 0xc9f50240) >> [ 12.273568] Stack: (0xc9f51e40 to 0xc9f52000) >> [ 12.278174] 1e40: c08cb478 00000000 00000200 00000000 200f0093 >> c08d853c c9f41e00 c9ebe380 >> [ 12.286808] 1e60: 00000000 c9ee9b80 c0c7db80 c9f50000 c9eeb700 >> c9ebe700 c9f51f24 c05994b8 >> [ 12.295440] 1e80: 00000004 c0250920 00000004 c0047954 d6266cd2 >> 00000002 00000000 00000000 >> [ 12.304074] 1ea0: 00000000 c0048854 c08cdb80 003b0000 d6266cd2 >> 00000002 00006ae1 c007a670 >> [ 12.312708] 1ec0: 00000139 00000000 0000b40e 0000b40e 00006a0d >> c007a670 f5257d14 c0079274 >> [ 12.321342] 1ee0: c9f41e00 00000000 00000003 0000081f c08ded98 >> bea94f88 c9f51fb0 000cf704 >> [ 12.329976] 1f00: c9f51f84 c9f51f60 c9f50028 c9ee9b80 00000000 >> c9f51f78 fffffff6 c9f50000 >> [ 12.338598] 1f20: c9f50000 c0048854 c9ee9dcc c9eeb700 c9f51f38 >> c9ee9e14 00000000 00000000 >> [ 12.347220] 1f40: 00000004 00000000 00000000 bea951a8 c9f50000 >> 00000000 000d6d64 c004988c >> [ 12.355841] 1f60: 00000003 00000004 00000000 00000000 bea951a8 >> 00000000 00000000 c9ee9b80 >> [ 12.364463] 1f80: c0047438 c9eeedd0 c9eeedd0 00000000 00000000 >> bea951a8 ffffffff 00000072 >> [ 12.373084] 1fa0: c000e344 c000e1a0 00000000 bea951a8 ffffffff >> bea951a8 00000000 00000000 >> [ 12.381705] 1fc0: 00000000 bea951a8 ffffffff 00000072 000cf704 >> 000d6094 00000000 000d6d64 >> [ 12.390328] 1fe0: 000cf164 bea95158 00045180 b6e37ae0 600f0010 >> ffffffff 2d10a02c c8542a0a >> [ 12.398987] [<c001dbd4>] (check_and_switch_context+0x3c0/0x44c) from >> [<c05994b8>] (__schedule+0x4ac/0x750) >> [ 12.409193] [<c05994b8>] (__schedule+0x4ac/0x750) from [<c0048854>] >> (do_wait+0x1ec/0x244) >> [ 12.417834] [<c0048854>] (do_wait+0x1ec/0x244) from [<c004988c>] >> (SyS_wait4+0xa8/0xc8) >> [ 12.426206] [<c004988c>] (SyS_wait4+0xa8/0xc8) from [<c000e1a0>] >> (ret_fast_syscall+0x0/0x30) >> [ 12.435116] Code: 1e082f13 f57ff04f f57ff06f e3a03000 (ee083f33) >> [ 12.441552] ---[ end trace c0816de7f5b496a8 ]--- >> >> I disassembled that faulting instruction manually just now, and it >> appears to be: >> >> 1110 1110 000 0 1000 0011 1111 001 1 0011 >> opc1 CRn Rt coproc opc2 CRm >> >> MCR cp15, 0, r3, c8, c3, 1 >> >> Which maps back to the call to dummt_flush_tlb_a15_erratum in >> check_and_switch_context: >> >> #ifdef CONFIG_ARM_ERRATA_798181 >> static inline void dummy_flush_tlb_a15_erratum(void) >> { >> /* >> * Dummy TLBIMVAIS. Using the unmapped address 0 and ASID 0. >> */ >> asm("mcr p15, 0, %0, c8, c3, 1" : : "r" (0)); >> dsb(); >> } >> #else >> static inline void dummy_flush_tlb_a15_erratum(void) >> { >> } >> #endif >> >> Now I think it's personally just easier to only turn on that errata on >> LPAE/A15 kernels and just leave it at that (I've requested this get >> moved to the lpae config and out of the base config so this is what >> should happen shortly - clearly the intention), but some folks out there >> want to do exciting things...I got asked if this could be runtime >> patched (which I guess in theory is possible), but I'm not going there. >> >> Anyway, in addition, does this kind of thing need fixing with a more >> specific Kconfig so that there's an explicit A15 dependency in there? >> Rather just "depends on CPU_V7 && SMP"? > > I think it needs to be run time detectable, according to Arnd if you > have a A15 kernel with < 4gb of RAM you don't want to run a LPAE > kernel as it's got quite decent performance penalties. I suppose the > other question to be asked is that as it's for A15 revisions > r0p0..r3p2 is whether how much of that silicon is about and if it was > never really widely available if we just disable it all together. > > Peter > _______________________________________________ > arm mailing list > arm@lists.fedoraproject.org > https://admin.fedoraproject.org/mailman/listinfo/arm