* Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> wrote: > Dave Hansen and I had some discussions on how to handle the nested NMI and > firmware calls. We thought of using a per cpu counter to record the nesting > call depth and toggle IBRS appropriately for the depth 0->1 and 1->0 transition. > Will this change be sufficient? Yeah, so I think the first question should be: does the firmware call from NMI context make sense to begin with? Because in this particular case it does not appear to be so: the reason for the BIOS/firmware call appears to be to determine how we nmi_panic() after receiving an NMI that no other NMI handler handled: with a passive-aggressive "I don't know" panic message or with a slightly more informative panic message. That's not a real value-add to users - so we can avoid all these complications by applying the patch below: drivers/watchdog/hpwdt.c | 30 ++++-------------------------- 1 file changed, 4 insertions(+), 26 deletions(-) As a bonus the spinlock use can be removed as well. Thanks, Ingo ====================> >From b038428a739a3fcf0b9678305c131f60af7422ca Mon Sep 17 00:00:00 2001 From: Ingo Molnar <mingo@xxxxxxxxxx> Date: Wed, 14 Feb 2018 10:24:41 +0100 Subject: [PATCH] watchdog: hpwdt: Remove spinlock acquire and BIOS calls from NMI context Taking a spinlock and calling into the firmware are problematic things to do from NMI callbacks. It also seems completely pointless in this particular case: - cmn_regs is updated by the firmware call in the hpwdt_pretimeout() NMI callback, but there's almost no use for it: we use it only to determine whether to panic with an 'unknown NMI' or a slightly more descriptive message. - cmn_regs and rom_lock is not used anywhere else, other than early detection of the firmware capability. So remove rom_lock, make the cmn_regs call from the detection routine only, and thus make the NMI callback a lot more robust. Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> --- drivers/watchdog/hpwdt.c | 30 ++++-------------------------- 1 file changed, 4 insertions(+), 26 deletions(-) diff --git a/drivers/watchdog/hpwdt.c b/drivers/watchdog/hpwdt.c index f1f00dfc0e68..2544fe482fe3 100644 --- a/drivers/watchdog/hpwdt.c +++ b/drivers/watchdog/hpwdt.c @@ -150,9 +150,7 @@ static unsigned int hpwdt_nmi_decoding; static unsigned int allow_kdump = 1; static unsigned int is_icru; static unsigned int is_uefi; -static DEFINE_SPINLOCK(rom_lock); static void *cru_rom_addr; -static struct cmn_registers cmn_regs; extern asmlinkage void asminline_call(struct cmn_registers *pi86Regs, unsigned long *pRomEntry); @@ -225,6 +223,7 @@ static int cru_detect(unsigned long map_entry, unsigned long physical_bios_base = 0; unsigned long physical_bios_offset = 0; int retval = -ENODEV; + struct cmn_registers cmn_regs = { }; bios32_map = ioremap(map_entry, (2 * PAGE_SIZE)); @@ -486,32 +485,18 @@ static int hpwdt_my_nmi(void) */ static int hpwdt_pretimeout(unsigned int ulReason, struct pt_regs *regs) { - unsigned long rom_pl; - static int die_nmi_called; - if (!hpwdt_nmi_decoding) return NMI_DONE; if ((ulReason == NMI_UNKNOWN) && !hpwdt_my_nmi()) return NMI_DONE; - spin_lock_irqsave(&rom_lock, rom_pl); - if (!die_nmi_called && !is_icru && !is_uefi) - asminline_call(&cmn_regs, cru_rom_addr); - die_nmi_called = 1; - spin_unlock_irqrestore(&rom_lock, rom_pl); - if (allow_kdump) hpwdt_stop(); - if (!is_icru && !is_uefi) { - if (cmn_regs.u1.ral == 0) { - nmi_panic(regs, "An NMI occurred, but unable to determine source.\n"); - return NMI_HANDLED; - } - } - nmi_panic(regs, "An NMI occurred. Depending on your system the reason " - "for the NMI is logged in any one of the following " + nmi_panic(regs, + "An NMI occurred. Depending on your system the reason " + "for the NMI might be logged in any one of the following " "resources:\n" "1. Integrated Management Log (IML)\n" "2. OA Syslog\n" @@ -744,13 +729,6 @@ static int hpwdt_init_nmi_decoding(struct pci_dev *dev) HPWDT_ARCH); return retval; } - - /* - * We know this is the only CRU call we need to make so lets keep as - * few instructions as possible once the NMI comes in. - */ - cmn_regs.u1.rah = 0x0D; - cmn_regs.u1.ral = 0x02; } /* -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html