Messages in this thread Patch in this message | | | Subject | Re: pstore does not work under xen | From | Boris Ostrovsky <> | Date | Mon, 23 Sep 2019 20:41:05 -0400 |
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On 9/23/19 6:59 PM, Kees Cook wrote: > On Mon, Sep 23, 2019 at 03:42:27PM +0000, James Dingwall wrote: >> On Thu, Sep 19, 2019 at 12:37:40PM -0400, Boris Ostrovsky wrote: >>> On 9/19/19 12:14 PM, James Dingwall wrote: >>>> On Thu, Sep 19, 2019 at 03:51:33PM +0000, Luck, Tony wrote: >>>>>> I have been investigating a regression in our environment where pstore >>>>>> (efi-pstore specifically but I suspect this would affect all >>>>>> implementations) no longer works after upgrading from a 4.4 to 5.0 >>>>>> kernel when running under xen. (This is an Ubuntu kernel but I don't >>>>>> think there are patches which affect this area.) >>>>> I don't have any answer for this ... but want to throw out the idea that >>>>> VMM systems could provide some hypercalls to guests to save/return >>>>> some blob of memory (perhaps the "save" triggers automagically if the >>>>> guest crashes?). >>>>> >>>>> That would provide a much better pstore back end than relying on emulation >>>>> of EFI persistent variables (which have severe contraints on size, and don't >>>>> support some pstore modes because you can't dynamically update EFI variables >>>>> hundreds of times per second). >>>>> >>>> For clarification this is a dom0 crash rather than an HVM guest with EFI. I >>>> should probably have also mentioned the xen verion has changed from 4.8.4 to >>>> 4.11.2 in case its behaviour on detection of crashed domain has changed. >>>> >>>> (For capturing guest crashes we have enabled xenconsole logging so the >>>> hvc0 log is available in dom0.) >>> >>> Do you only see this difference between 4.4 and 5.0 when you crash via >>> sysrq? >>> >>> Because that's where things changed. On 4.4 we seem to be forcing an >>> oops, which eventually calls kmsg_dump() and then panic. On 5.0 we call >>> panic() directly from sysrq handler. And because Xen's panic notifier >>> doesn't return we never get a chance to call kmsg_dump(). >>> >> Ok, I see that change in 8341f2f222d729688014ce8306727fdb9798d37e. I >> hadn't tested it any other way before. Using the null pointer >> de-reference module code at [1] a pstore record is generated as expected >> when the module is loaded (panic_on_oops=1). > This change looks correct -- it just gets us directly to the panic() > state instead of exercising the various exception handlers. > >> I have also tested swapping the kmsg_dump() / >> atomic_notifier_call_chain() around in panic.c and this also results in >> a pstore record being created with sysrq-c. I don't know if that would >> be an acceptable solution though since it may break behaviour that other >> things depend on. > I don't think reordering these is a good idea: as the comments say, > there might be work done in the notifier chain that kmsg_dump() will > want to capture (e.g. the KASLR base offset). > > The situation seems to be that notifier callbacks must return -- I think > Xen needs fixing here. >
I only had one quick sanity test with a PV guest so this needs more testing. James, can you give it a try?
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c index 750f46ad018a..d88f118028b4 100644 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -269,16 +269,17 @@ void xen_reboot(int reason) BUG(); } +static int reboot_reason = SHUTDOWN_reboot; void xen_emergency_restart(void) { - xen_reboot(SHUTDOWN_reboot); + xen_reboot(reboot_reason); } static int xen_panic_event(struct notifier_block *this, unsigned long event, void *ptr) { if (!kexec_crash_loaded()) - xen_reboot(SHUTDOWN_crash); + reboot_reason = SHUTDOWN_crash; return NOTIFY_DONE; } @@ -290,6 +291,8 @@ static struct notifier_block xen_panic_block = { int xen_panic_handler_init(void) { atomic_notifier_chain_register(&panic_notifier_list, &xen_panic_block); + if (panic_timeout == 0) + set_arch_panic_timeout(-1, CONFIG_PANIC_TIMEOUT); return 0; }
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