The first attachment is the config I initially used last night after that second patch (removing 'local' etc.). As you guessed, all four options are set, hence the name of the file (ending in '-y'). The other config I'm attaching was treated as you lay out (2-config-n). I used the '-n' config to compile two kernels just now: (a) e802a51, that same first commit giving me trouble. The changes made no difference to kexec behaviour: with the e802a51 kernel calling kexec boot directly with -e and triggering a panic both kick off a full reboot, though the crash kernel registers as loaded. (b) the kernel in the branch I made last night, with the set_idt kexec (for good measure, I thought I might as well do this one too). No difference here either: the crash dump kernel boots fine both ways (directly and upon intentional crashing). On Sun, Dec 24, 2017 at 12:28:17PM +0100, Ingo Molnar wrote: > > * Alexandru Chirvasitu wrote: > > > Thank you for the swift reply! > > > > On Sat, Dec 23, 2017 at 07:30:21PM -0800, Linus Torvalds wrote: > > > On Sat, Dec 23, 2017 at 5:44 PM, Alexandru Chirvasitu > > > wrote: > > > > > > > > For testing purposes, I've altered machine_kexec_32.c making the > > > > following toy commit. It naively undoes part of e802a51, solely to > > > > confirm that's where it goes awry in my setup. > > > > > > That's really funky. > > > > > > The idt_invalidate() seems to do *exactly* the same thing. It uses > > > "load_idt()" on an IDT with size 0, and the supplied address. > > > > > > Can you disassemble your "set_idt()" code vs the "idt_invalidate()"? > > > > > > > I seem to have done some such thing just now, but please excuse some > > poking around in the dark here (I've disassembled code exactly once > > before: yesterday, in answering a similar request for more info in > > another lkml thread..). > > > > I'm actually not even certain the sequel is what you are asking. > > > > I couldn't find the set_idt symbol in > > arch/x86/kernel/machine_kexec_32.o. Google seemed to think this has > > something to do with the 'static' marker for that function, so I made > > another commit differing from the previous one only in that it removes > > that marker (i.e. set_idt is now 'void' rather than 'static void'). > > > > I can now see that function with objdump. The relevant sections of > > objdump -D on the two files are: > > > > --- arch/x86/kernel/machine_kexec_32.o --- > > > > 00000180 : > > 180: e8 fc ff ff ff call 181 > > 185: 55 push %ebp > > 186: 89 e5 mov %esp,%ebp > > 188: 83 ec 0c sub $0xc,%esp > > 18b: 89 45 f8 mov %eax,-0x8(%ebp) > > 18e: 66 89 55 f6 mov %dx,-0xa(%ebp) > > 192: 8d 45 f6 lea -0xa(%ebp),%eax > > 195: 65 8b 0d 14 00 00 00 mov %gs:0x14,%ecx > > 19c: 89 4d fc mov %ecx,-0x4(%ebp) > > 19f: 31 c9 xor %ecx,%ecx > > 1a1: ff 15 20 00 00 00 call *0x20 > > 1a7: 8b 45 fc mov -0x4(%ebp),%eax > > 1aa: 65 33 05 14 00 00 00 xor %gs:0x14,%eax > > 1b1: 75 02 jne 1b5 > > 1b3: c9 leave > > 1b4: c3 ret > > 1b5: e8 fc ff ff ff call 1b6 > > 1ba: 8d b6 00 00 00 00 lea 0x0(%esi),%esi > > > > ---------------------------------------------- > > > > and > > > > --- arch/x86/kernel/idt.o --- > > > > 00000000 : > > 0: e8 fc ff ff ff call 1 > > 5: 55 push %ebp > > 6: 89 e5 mov %esp,%ebp > > 8: 83 ec 0c sub $0xc,%esp > > b: 65 8b 15 14 00 00 00 mov %gs:0x14,%edx > > 12: 89 55 fc mov %edx,-0x4(%ebp) > > 15: 31 d2 xor %edx,%edx > > 17: 31 d2 xor %edx,%edx > > 19: 89 45 f8 mov %eax,-0x8(%ebp) > > 1c: 8d 45 f6 lea -0xa(%ebp),%eax > > 1f: 66 89 55 f6 mov %dx,-0xa(%ebp) > > 23: ff 15 20 00 00 00 call *0x20 > > 29: 8b 45 fc mov -0x4(%ebp),%eax > > 2c: 65 33 05 14 00 00 00 xor %gs:0x14,%eax > > 33: 75 02 jne 37 > > 35: c9 leave > > 36: c3 ret > > 37: e8 fc ff ff ff call 38 > > > > ------------------------------- > > > > I've also checked again that this newer compilation still gives a > > well-behaved kexec. > > So guessing from the disassembly your kernel config seems to have both function > tracing and paravirt enabled - both can cause complications here, in particular > paravirt may override load_idt(). > > ( In the end execution should run through the same paravirt ops with and without > your patch, so I don't see how it can make a difference but it's easier to look > at the disassembly without the paravirt indirection - and your patch obviously > makes a difference so we are missing some detail. ) > > So to simplify analysis, could you disable both please - i.e. disable these if > your .config has any of these set: > > CONFIG_HYPERVISOR_GUEST=y > CONFIG_FUNCTION_TRACER=y > CONFIG_STACK_TRACER=y > CONFIG_FUNCTION_GRAPH_TRACER=y > > The easiest way to disable these is to run this script over your .config, in the > kernel source code directory where you are building your kernel: > > grep -vE 'CONFIG_HYPERVISOR_GUEST|CONFIG_FUNCTION_TRACER|CONFIG_STACK_TRACER|CONFIG_FUNCTION_GRAPH_TRACER' .config > .config2 > /bin/mv .config2 .config > > ... then run 'make oldconfig' and answer 'N' to every question. Double check the > resulting .config via: > > grep -E 'CONFIG_HYPERVISOR_GUEST|CONFIG_FUNCTION_TRACER|CONFIG_STACK_TRACER|CONFIG_FUNCTION_GRAPH_TRACER' .config > > which should output: > > # CONFIG_HYPERVISOR_GUEST is not set > # CONFIG_FUNCTION_TRACER is not set > # CONFIG_STACK_TRACER is not set > > Also, could you send us your .config? > > Thanks, > > Ingo