From: Mark Rutland <mark.rutland@arm.com> [Upstream commit 614ab80c96474682157cabb14f8c8602b3422e90] When a kernel is built with CONFIG_ARM64_PSEUDO_NMI=y and pseudo-NMIs are enabled at runtime, GICv3's gic_handle_irq() can leave DAIF and ICC_PMR_EL1 in an unexpected state in some cases, breaking subsequent usage of local_irq_enable() and resulting in softirqs being run with IRQs erroneously masked (possibly resulting in deadlocks). This can happen when an IRQ exception is taken from a context where regular IRQs were unmasked, and either: (1) ICC_IAR1_EL1 indicates a special INTID (e.g. as a result of an IRQ being withdrawn since the IRQ exception was taken). (2) ICC_IAR1_EL1 and ICC_RPR_EL1 indicate an NMI was acknowledged. When an NMI is taken from a context where regular IRQs were masked, there is no problem. When CONFIG_ARM64_DEBUG_PRIORITY_MASKING=y, this can be detected with perf, e.g. | # ./perf record -a -g -e cycles:k ls -alR / > /dev/null 2>&1 | ------------[ cut here ]------------ | WARNING: CPU: 0 PID: 14 at arch/arm64/include/asm/irqflags.h:32 arch_local_irq_enable+0x4c/0x6c | Modules linked in: | CPU: 0 PID: 14 Comm: ksoftirqd/0 Not tainted 5.18.0-rc5-00004-g876c38e3d20b #12 | Hardware name: linux,dummy-virt (DT) | pstate: 204000c5 (nzCv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--) | pc : arch_local_irq_enable+0x4c/0x6c | lr : __do_softirq+0x110/0x5d8 | sp : ffff8000080bbbc0 | pmr_save: 000000f0 | x29: ffff8000080bbbc0 x28: ffff316ac3a6ca40 x27: 0000000000000000 | x26: 0000000000000000 x25: ffffa04611c06008 x24: ffffa04611c06008 | x23: 0000000040400005 x22: 0000000000000200 x21: ffff8000080bbe20 | x20: ffffa0460fe10320 x19: 0000000000000009 x18: 0000000000000000 | x17: ffff91252dfa9000 x16: ffff800008004000 x15: 0000000000004000 | x14: 0000000000000028 x13: ffffa0460fe17578 x12: ffffa0460fed4294 | x11: ffffa0460fedc168 x10: ffffffffffffff80 x9 : ffffa0460fe10a70 | x8 : ffffa0460fedc168 x7 : 000000000000b762 x6 : 00000000057c3bdf | x5 : ffff8000080bbb18 x4 : 0000000000000000 x3 : 0000000000000001 | x2 : ffff91252dfa9000 x1 : 0000000000000060 x0 : 00000000000000f0 | Call trace: | arch_local_irq_enable+0x4c/0x6c | __irq_exit_rcu+0x180/0x1ac | irq_exit_rcu+0x1c/0x44 | el1_interrupt+0x4c/0xe4 | el1h_64_irq_handler+0x18/0x24 | el1h_64_irq+0x74/0x78 | smpboot_thread_fn+0x68/0x2c0 | kthread+0x124/0x130 | ret_from_fork+0x10/0x20 | irq event stamp: 193241 | hardirqs last enabled at (193240): [<ffffa0460fe10a9c>] __do_softirq+0x10c/0x5d8 | hardirqs last disabled at (193241): [<ffffa0461102ffe4>] el1_dbg+0x24/0x90 | softirqs last enabled at (193234): [<ffffa0460fe10e00>] __do_softirq+0x470/0x5d8 | softirqs last disabled at (193239): [<ffffa0460fea9944>] __irq_exit_rcu+0x180/0x1ac | ---[ end trace 0000000000000000 ]--- The necessary manipulation of DAIF and ICC_PMR_EL1 depends on the interrupted context, but the structure of gic_handle_irq() makes this also depend on whether the GIC reports an IRQ, NMI, or special INTID: * When the interrupted context had regular IRQs masked (and hence the interrupt must be an NMI), the entry code performs the NMI entry/exit and gic_handle_irq() should return with DAIF and ICC_PMR_EL1 unchanged. This is handled correctly today. * When the interrupted context had regular IRQs unmasked, the entry code performs IRQ entry/exit, but expects gic_handle_irq() to always update ICC_PMR_EL1 and DAIF.IF to unmask NMIs (but not regular IRQs) prior to returning (which it must do prior to invoking any regular IRQ handler). This unbalanced calling convention is necessary because we don't know whether an NMI has been taken until acknowledged by a read from ICC_IAR1_EL1, and so we need to perform the read with NMI masked in case an NMI has been taken (and needs to be handled with NMIs masked). Unfortunately, this is not handled consistently: - When ICC_IAR1_EL1 reports a special INTID, gic_handle_irq() returns immediately without manipulating ICC_PMR_EL1 and DAIF. - When RPR_EL1 indicates an NMI, gic_handle_irq() calls gic_handle_nmi() to invoke the NMI handler, then returns without manipulating ICC_PMR_EL1 and DAIF. - For regular IRQs, gic_handle_irq() manipulates ICC_PMR_EL1 and DAIF prior to invoking the IRQ handler. There were related problems with special INTID handling in the past, where if an exception was taken from a context with regular IRQs masked and ICC_IAR_EL1 reported a special INTID, gic_handle_irq() would erroneously unmask NMIs in NMI context permitted an unexpected nested NMI. That case specifically was fixed by commit: a97709f563a078e2 ("irqchip/gic-v3: Do not enable irqs when handling spurious interrups") ... but unfortunately that commit added an inverse problem, where if an exception was taken from a context with regular IRQs *unmasked* and ICC_IAR_EL1 reported a special INTID, gic_handle_irq() would erroneously fail to unmask NMIs (and consequently regular IRQs could not be unmasked during softirq processing). Before and after that commit, if an NMI was taken from a context with regular IRQs unmasked gic_handle_irq() would not unmask NMIs prior to returning, leading to the same problem with softirq handling. This patch fixes this by restructuring gic_handle_irq(), splitting it into separate irqson/irqsoff helper functions which consistently perform the DAIF + ICC_PMR1_EL1 manipulation based upon the interrupted context, regardless of the event indicated by ICC_IAR1_EL1. The special INTID handling is moved into the low-level IRQ/NMI handler invocation helper functions, so that early returns don't prevent the required manipulation of DAIF + ICC_PMR_EL1. Fixes: f32c926651dcd168 ("irqchip/gic-v3: Handle pseudo-NMIs") Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Marc Zyngier <maz@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Marc Zyngier <maz@kernel.org> Link: https://lore.kernel.org/r/20220513133038.226182-4-mark.rutland@arm.com --- drivers/irqchip/irq-gic-v3.c | 138 +++++++++++++++++++++++++---------- 1 file changed, 101 insertions(+), 37 deletions(-) diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c index 3f440dcb3523..5b57493f02b2 100644 --- a/drivers/irqchip/irq-gic-v3.c +++ b/drivers/irqchip/irq-gic-v3.c @@ -600,50 +600,23 @@ static inline void gic_complete_ack(u32 irqnr) isb(); } -static inline void gic_handle_nmi(u32 irqnr, struct pt_regs *regs) +static bool gic_rpr_is_nmi_prio(void) { - bool irqs_enabled = interrupts_enabled(regs); - int err; - - if (irqs_enabled) - nmi_enter(); - - gic_complete_ack(irqnr); - - /* - * Leave the PSR.I bit set to prevent other NMIs to be - * received while handling this one. - * PSR.I will be restored when we ERET to the - * interrupted context. - */ - err = handle_domain_nmi(gic_data.domain, irqnr, regs); - if (err) - gic_deactivate_unhandled(irqnr); + if (!gic_supports_nmi()) + return false; - if (irqs_enabled) - nmi_exit(); + return unlikely(gic_read_rpr() == GICD_INT_NMI_PRI); } -static asmlinkage void __exception_irq_entry gic_handle_irq(struct pt_regs *regs) +static bool gic_irqnr_is_special(u32 irqnr) { - u32 irqnr; - - irqnr = gic_read_iar(); - - /* Check for special IDs first */ - if ((irqnr >= 1020 && irqnr <= 1023)) - return; + return irqnr >= 1020 && irqnr <= 1023; +} - if (gic_supports_nmi() && - unlikely(gic_read_rpr() == GICD_INT_NMI_PRI)) { - gic_handle_nmi(irqnr, regs); +static void __gic_handle_irq(u32 irqnr, struct pt_regs *regs) +{ + if (gic_irqnr_is_special(irqnr)) return; - } - - if (gic_prio_masking_enabled()) { - gic_pmr_mask_irqs(); - gic_arch_enable_irqs(); - } /* Treat anything but SGIs in a uniform way */ if (likely(irqnr > 15)) { @@ -675,6 +648,97 @@ static asmlinkage void __exception_irq_entry gic_handle_irq(struct pt_regs *regs WARN_ONCE(true, "Unexpected SGI received!\n"); #endif } + +} + +static void __gic_handle_nmi(u32 irqnr, struct pt_regs *regs) +{ + if (gic_irqnr_is_special(irqnr)) + return; + + gic_complete_ack(irqnr); + + if (handle_domain_nmi(gic_data.domain, irqnr, regs)) + gic_deactivate_unhandled(irqnr); +} + +/* + * An exception has been taken from a context with IRQs enabled, and this could + * be an IRQ or an NMI. + * + * The entry code called us with DAIF.IF set to keep NMIs masked. We must clear + * DAIF.IF (and update ICC_PMR_EL1 to mask regular IRQs) prior to returning, + * after handling any NMI but before handling any IRQ. + * + * The entry code has performed IRQ entry, and if an NMI is detected we must + * perform NMI entry/exit around invoking the handler. + */ +static void __gic_handle_irq_from_irqson(struct pt_regs *regs) +{ + bool is_nmi; + u32 irqnr; + + irqnr = gic_read_iar(); + + is_nmi = gic_rpr_is_nmi_prio(); + + if (is_nmi) { + nmi_enter(); + __gic_handle_nmi(irqnr, regs); + nmi_exit(); + } + + if (gic_prio_masking_enabled()) { + gic_pmr_mask_irqs(); + gic_arch_enable_irqs(); + } + + if (!is_nmi) + __gic_handle_irq(irqnr, regs); +} + +/* + * An exception has been taken from a context with IRQs disabled, which can only + * be an NMI. + * + * The entry code called us with DAIF.IF set to keep NMIs masked. We must leave + * DAIF.IF (and ICC_PMR_EL1) unchanged. + * + * The entry code has performed NMI entry. + */ +static void __gic_handle_irq_from_irqsoff(struct pt_regs *regs) +{ + u64 pmr; + u32 irqnr; + + /* + * We were in a context with IRQs disabled. However, the + * entry code has set PMR to a value that allows any + * interrupt to be acknowledged, and not just NMIs. This can + * lead to surprising effects if the NMI has been retired in + * the meantime, and that there is an IRQ pending. The IRQ + * would then be taken in NMI context, something that nobody + * wants to debug twice. + * + * Until we sort this, drop PMR again to a level that will + * actually only allow NMIs before reading IAR, and then + * restore it to what it was. + */ + pmr = gic_read_pmr(); + gic_pmr_mask_irqs(); + isb(); + irqnr = gic_read_iar(); + gic_write_pmr(pmr); + + __gic_handle_nmi(irqnr, regs); +} + +static asmlinkage void __exception_irq_entry gic_handle_irq(struct pt_regs *regs) +{ + if (unlikely(gic_supports_nmi() && !interrupts_enabled(regs))) + __gic_handle_irq_from_irqsoff(regs); + else + __gic_handle_irq_from_irqson(regs); } static u32 gic_get_pribits(void) -- 2.25.1