On Thu, Feb 18, 2021 at 09:51:40PM +0900, Hector Martin wrote: > On 17/02/2021 21.22, Mark Rutland wrote: > > > Root irqchip drivers can discriminate between IRQs and FIQs by checking > > > the ISR_EL1 system register. > > > > I think we can remove this note for now. If we go with seperate handlers > > this won't be necessary, and if not this would be better placed on a > > commit adding the FIQ handling capability. > > Indeed, this doesn't make sense any more. Changed for v3. > > > Judging by `git grep -Wi daif -- arch/arm64`, with this patch applied, > > we'll also need fixups in: > > > > * gic_arch_enable_irqs() in arch/arm64/include/asm/arch_gicv3.h > > * save_and_disable_irq() in arch/arm64/include/asm/assembler.h (noted below) > > * local_daif_save_flags() in arch/arm64/include/asm/daifflags.h > > (the fake DAIF should have F set too) > > * __cpu_do_idle_irqprio() in arch/arm64/kernel/process.c > > Good catches. A few of those are irrelevant for M1 but need to be done now > that we're making this change globally, others I just missed from the > beginning. Sure; my general view is that we should aim for consistency, and should ensure that DAIF.F==DAIF.I at all times on all platforms unless we have a strong reason to violate that rule. That generally makes it easier to reason about the code and avoid accidentally breaking M1/non-M1 if/when we refactor masking logic. > There's also an incorrect comment in entry.S: > > /* > * DA_F were cleared at start of handling. If anything is set in > * DAIF, we come back from an NMI, so skip preemption > */ > mrs x0, daif > orr x24, x24, x0 > > Now only DA__ are cleared. This actually pairs with gic_arch_enable_irqs() > and begs the question: in priority masking systems, do we unmask both IRQ > and FIQ (the gic_arch_enable_irqs change), or do we leave FIQ masked (which > instead would need an AND in that part of entry.S so as to not consider FIQ > masked as meaning we're coming back from an NMI)? I think that for consistency we always want to keep IRQ and FIQ in-sync, even when using GIC priorities. So when handling a pseudo-NMI we should unmask DAIF.DA and leave DAIF.IF masked. > And a minor related one: should init_gic_priority_masking() WARN if FIQ is > masked too? This probably goes with the above. I think it should, yes. > Either way, this was nontrivial to make sense of, so I'll make that entry.S > comment clearer while I'm touching it. Sounds good; thanks! > > I think save_and_diable_irq below needs to be updated too, since it > > only sets DAIF.I and leaves DAIF.F as-is. > > Totally missed this one! Fixed for v3. > > > > - * FIQ is never expected, but we mask it when we disable debug exceptions, and > > > - * unmask it at all other times. > > > + * FIQ is never expected on most platforms, but we keep it synchronized > > > + * with the IRQ mask status. On platforms that do not expect FIQ, that vector > > > + * triggers a kernel panic. On platforms that do, the FIQ vector is unified > > > + * with the IRQ vector. > > > */ > > > > Can we please delete this bit, though? Now that we say IRQ and FIQ are > > masked/unmasked together, I don't think the rest is necessary to > > understand the masking logic, and it's one less thing to keep in sync > > with changes to the entry code. > > Gone :) Thanks, Mark.
