From c6875f3aacf2a5a913205accddabf0bfb75cac76 Mon Sep 17 00:00:00 2001 From: Boris Ostrovsky Date: Mon, 30 Sep 2019 16:44:41 -0400 Subject: [PATCH] x86/xen: Return from panic notifier Currently execution of panic() continues until Xen's panic notifier (xen_panic_event()) is called at which point we make a hypercall that never returns. This means that any notifier that is supposed to be called later as well as significant part of panic() code (such as pstore writes from kmsg_dump()) is never executed. There is no reason for xen_panic_event() to be this last point in execution since panic()'s emergency_restart() will call into xen_emergency_restart() from where we can perform our hypercall. Nevertheless, we will provide xen_legacy_crash boot option that will preserve original behavior during crash. This option could be used, for example, if running kernel dumper (which happens after panic notifiers) is undesirable. Reported-by: James Dingwall Signed-off-by: Boris Ostrovsky Reviewed-by: Juergen Gross --- .../admin-guide/kernel-parameters.txt | 4 +++ arch/x86/xen/enlighten.c | 28 +++++++++++++++++-- 2 files changed, 29 insertions(+), 3 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 4c1971960afa..5ea005c9e2d6 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -5267,6 +5267,10 @@ the unplug protocol never -- do not unplug even if version check succeeds + xen_legacy_crash [X86,XEN] + Crash from Xen panic notifier, without executing late + panic() code such as dumping handler. + xen_nopvspin [X86,XEN] Disables the ticketlock slowpath using Xen PV optimizations. diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c index 750f46ad018a..205b1176084f 100644 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -269,19 +269,41 @@ void xen_reboot(int reason) BUG(); } +static int reboot_reason = SHUTDOWN_reboot; +static bool xen_legacy_crash; 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); + if (!kexec_crash_loaded()) { + if (xen_legacy_crash) + xen_reboot(SHUTDOWN_crash); + + reboot_reason = SHUTDOWN_crash; + + /* + * If panic_timeout==0 then we are supposed to wait forever. + * However, to preserve original dom0 behavior we have to drop + * into hypervisor. (domU behavior is controlled by its + * config file) + */ + if (panic_timeout == 0) + panic_timeout = -1; + } return NOTIFY_DONE; } +static int __init parse_xen_legacy_crash(char *arg) +{ + xen_legacy_crash = true; + return 0; +} +early_param("xen_legacy_crash", parse_xen_legacy_crash); + static struct notifier_block xen_panic_block = { .notifier_call = xen_panic_event, .priority = INT_MIN