From: Julien Thierry <julien.thierry@arm.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: linux-arm-kernel@lists.infradead.org, daniel.thompson@linaro.org,
marc.zyngier@arm.com, will.deacon@arm.com,
linux-kernel@vger.kernel.org, christoffer.dall@arm.com,
james.morse@arm.com, joel@joelfernandes.org
Subject: Re: [PATCH v6 15/24] arm64: Switch to PMR masking when starting CPUs
Date: Tue, 4 Dec 2018 18:11:53 +0000 [thread overview]
Message-ID: <ffb17cfd-d941-1df6-8b41-2f710948e9b2@arm.com> (raw)
In-Reply-To: <20181204175142.GD19210@arrakis.emea.arm.com>
On 04/12/18 17:51, Catalin Marinas wrote:
> On Mon, Nov 12, 2018 at 11:57:06AM +0000, Julien Thierry wrote:
>> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
>> index 8dc9dde..e495360 100644
>> --- a/arch/arm64/kernel/smp.c
>> +++ b/arch/arm64/kernel/smp.c
>> @@ -35,6 +35,7 @@
>> #include <linux/smp.h>
>> #include <linux/seq_file.h>
>> #include <linux/irq.h>
>> +#include <linux/irqchip/arm-gic-v3.h>
>> #include <linux/percpu.h>
>> #include <linux/clockchips.h>
>> #include <linux/completion.h>
>> @@ -175,6 +176,25 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
>> return ret;
>> }
>>
>> +static void init_gic_priority_masking(void)
>> +{
>> + u32 gic_sre = gic_read_sre();
>> + u32 cpuflags;
>> +
>> + if (WARN_ON(!(gic_sre & ICC_SRE_EL1_SRE)))
>> + return;
>> +
>> + WARN_ON(!irqs_disabled());
>> +
>> + gic_write_pmr(GIC_PRIO_IRQOFF);
>> +
>> + cpuflags = read_sysreg(daif);
>> +
>> + /* We can only unmask PSR.I if we can take aborts */
>> + if (!(cpuflags & PSR_A_BIT))
>> + write_sysreg(cpuflags & ~PSR_I_BIT, daif);
>
> I don't understand this. If you don't switch off PSR_I_BIT here, where
> does it happen? In which scenario do we actually have the A bit still
> set? At a quick look, smp_prepare_boot_cpu() would have the A bit
> cleared previously by setup_arch(). We have secondary_start_kernel()
> where you call init_gic_priority_masking() before local_daif_restore().
>
So this is for secondary CPUs where PSR.A can be still set.
The thing is that the daifflags.h establishes the order for disabling
types of exceptions:
Debug > Abort > IRQ
The idea is that when introducing pseudo-NMIs this becomes:
Debug > Abort > pseudo-NMI > IRQ
Whenever aborts are disabled (maybe because we just took an abort) we
don't want to take an NMI.
> So what happens if you always turn off PSR_I_BIT here?
>
So semantically it would be saying "we can take a pseudo-NMI here".
Realistically, I think it depends on the state of the GIC redistributor
for this CPU:
- If the re-distributor was initialized, nothing bad could happen as no
NMI could have been configured for this CPU yet.
- If the re-distributor initialization is done between the call to
init_gic_priority_mask() and the local_daif_restore() then probably bad
things could happen
I can try to figure out if it is safe to just clear PSR.I always, but I
also find it easier to always play by the rule "if PSR.A is set, PSR.I
is set".
Thanks,
--
Julien Thierry
next prev parent reply other threads:[~2018-12-04 18:11 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-12 11:56 [PATCH v6 00/24] arm64: provide pseudo NMI with GICv3 Julien Thierry
2018-11-12 11:56 ` [PATCH v6 01/24] arm64: Remove unused daif related functions/macros Julien Thierry
2018-11-29 16:26 ` Mark Rutland
2018-11-30 18:03 ` Catalin Marinas
2018-11-12 11:56 ` [PATCH v6 02/24] arm64: cpufeature: Set SYSREG_GIC_CPUIF as a boot system feature Julien Thierry
2018-11-12 18:00 ` Suzuki K Poulose
2018-11-29 16:27 ` Mark Rutland
2018-11-30 18:07 ` Catalin Marinas
2018-11-12 11:56 ` [PATCH v6 03/24] arm64: cpufeature: Add cpufeature for IRQ priority masking Julien Thierry
2018-11-12 18:02 ` Suzuki K Poulose
2018-11-29 17:12 ` Mark Rutland
2018-12-03 10:33 ` Julien Thierry
2018-11-30 18:07 ` Catalin Marinas
2018-11-12 11:56 ` [PATCH v6 04/24] arm/arm64: gic-v3: Add PMR and RPR accessors Julien Thierry
2018-11-29 16:32 ` Mark Rutland
2018-11-30 18:07 ` Catalin Marinas
2018-11-12 11:56 ` [PATCH v6 05/24] irqchip/gic-v3: Switch to PMR masking before calling IRQ handler Julien Thierry
2018-11-29 18:12 ` Mark Rutland
2018-11-30 9:18 ` Julien Thierry
2018-12-04 16:21 ` Catalin Marinas
2018-11-12 11:56 ` [PATCH v6 06/24] arm64: ptrace: Provide definitions for PMR values Julien Thierry
2018-11-29 16:40 ` Mark Rutland
2018-11-30 8:53 ` Julien Thierry
2018-11-30 10:38 ` Daniel Thompson
2018-11-30 11:03 ` Julien Thierry
2018-11-12 11:56 ` [PATCH v6 07/24] arm64: Make PMR part of task context Julien Thierry
2018-11-29 16:46 ` Mark Rutland
2018-11-30 9:25 ` Julien Thierry
2018-12-04 17:09 ` Catalin Marinas
2018-12-04 17:30 ` Julien Thierry
2018-11-12 11:56 ` [PATCH v6 08/24] arm64: Unmask PMR before going idle Julien Thierry
2018-11-29 17:44 ` Mark Rutland
2018-11-30 10:55 ` Julien Thierry
2018-11-30 13:37 ` Mark Rutland
2018-12-03 10:38 ` Julien Thierry
2018-11-12 11:57 ` [PATCH v6 09/24] arm64: kvm: Unmask PMR before entering guest Julien Thierry
2018-11-12 11:57 ` [PATCH v6 10/24] arm64: irqflags: Use ICC_PMR_EL1 for interrupt masking Julien Thierry
2018-12-04 17:36 ` Catalin Marinas
2018-12-05 16:55 ` Julien Thierry
2018-12-05 18:26 ` Catalin Marinas
2018-12-06 9:50 ` Julien Thierry
2018-12-10 14:39 ` Catalin Marinas
2018-11-12 11:57 ` [PATCH v6 11/24] arm64: daifflags: Include PMR in daifflags restore operations Julien Thierry
2018-11-12 11:57 ` [PATCH v6 12/24] arm64: alternative: Allow alternative status checking per cpufeature Julien Thierry
2018-11-12 11:57 ` [PATCH v6 13/24] arm64: alternative: Apply alternatives early in boot process Julien Thierry
2018-11-12 11:57 ` [PATCH v6 14/24] irqchip/gic-v3: Factor group0 detection into functions Julien Thierry
2018-11-12 11:57 ` [PATCH v6 15/24] arm64: Switch to PMR masking when starting CPUs Julien Thierry
2018-12-04 17:51 ` Catalin Marinas
2018-12-04 18:11 ` Julien Thierry [this message]
2018-11-12 11:57 ` [PATCH v6 16/24] arm64: gic-v3: Implement arch support for priority masking Julien Thierry
2018-11-12 11:57 ` [PATCH v6 17/24] irqchip/gic-v3: Detect if GIC can support pseudo-NMIs Julien Thierry
2018-11-12 11:57 ` [PATCH v6 18/24] irqchip/gic-v3: Handle pseudo-NMIs Julien Thierry
2018-11-12 11:57 ` [PATCH v6 19/24] irqchip/gic: Add functions to access irq priorities Julien Thierry
2018-11-12 11:57 ` [PATCH v6 20/24] irqchip/gic-v3: Allow interrupts to be set as pseudo-NMI Julien Thierry
2018-11-12 11:57 ` [PATCH v6 21/24] arm64: Handle serror in NMI context Julien Thierry
2018-12-04 18:09 ` Catalin Marinas
2018-12-05 13:02 ` James Morse
2018-11-12 11:57 ` [PATCH v6 22/24] arm64: Skip preemption when exiting an NMI Julien Thierry
2018-11-12 11:57 ` [PATCH v6 23/24] arm64: Skip irqflags tracing for NMI in IRQs disabled context Julien Thierry
2018-11-12 11:57 ` [PATCH v6 24/24] arm64: Enable the support of pseudo-NMIs Julien Thierry
2018-11-12 12:00 ` [PATCH v6 00/24] arm64: provide pseudo NMI with GICv3 Julien Thierry
2018-11-13 14:43 ` Julien Thierry
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