From: James Morse <james.morse@arm.com>
To: Daniel Thompson <daniel.thompson@linaro.org>,
Julien Thierry <julien.thierry@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, joel@joelfernandes.org,
marc.zyngier@arm.com, mark.rutland@arm.com,
christoffer.dall@arm.com, catalin.marinas@arm.com,
will.deacon@arm.com
Subject: Re: [PATCH v5 03/27] arm64: alternative: Apply alternatives early in boot process
Date: Tue, 18 Sep 2018 18:47:43 +0100 [thread overview]
Message-ID: <46463b3d-7ceb-f5a5-4061-e988bfc53a6e@arm.com> (raw)
In-Reply-To: <20180917234400.ctq3w2u6fi5s5coj@holly.lan>
Hi Daniel, Julien,
On 09/18/2018 12:44 AM, Daniel Thompson wrote:
> On Wed, Sep 12, 2018 at 05:49:09PM +0100, Julien Thierry wrote:
>>>> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
>>>> index 3bc1c8b..0d1e41e 100644
>>>> --- a/arch/arm64/kernel/cpufeature.c
>>>> +++ b/arch/arm64/kernel/cpufeature.c
>>>> @@ -52,6 +52,8 @@
>>>> DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS);
>>>> EXPORT_SYMBOL(cpu_hwcaps);
>>>> +unsigned long boot_capabilities;
>>>> +
>>>> /*
>>>> * Flag to indicate if we have computed the system wide
>>>> * capabilities based on the boot time active CPUs. This
>>>> @@ -1375,6 +1377,9 @@ static void __update_cpu_capabilities(const struct arm64_cpu_capabilities *caps,
>>>> if (!cpus_have_cap(caps->capability) && caps->desc)
>>>> pr_info("%s %s\n", info, caps->desc);
>>>> cpus_set_cap(caps->capability);
>>>
>>> Hmm, the bitmap behind cpus_set_cap() is what cpus_have_cap() in
>>> __apply_alternatives() looks at. If you had a call to __apply_alternatives after
>>> update_cpu_capabilities(SCOPE_BOOT_CPU), but before any others, it would only
>>> apply those alternatives...
>>>
>>> (I don't think there is a problem re-applying the same alternative, but I
>>> haven't checked).
>> Interesting idea. If someone can confirm that patching alternatives twice is
>> safe, I think it would make things simpler.
Sounds good, I think we need to avoid adding a limit to the number of caps.
The extra-work is inefficient, but if it saves merging those lists as part of this
series its probably fine. (we only do this stuff once during boot)
> Early versions of this patch applied the alternatives twice. I never
> noticed any problems with double patching (second time round it will
> write out code that is identical to what is already there so it is
> merely inefficient rather than unsafe.
For the regular kind, I agree. But we've recently grown some fancy dynamic patching
where the code is generated at runtime, instead of swapping in an alternative
sequence. Details in commit dea5e2a4 ("arm64: alternatives: Add dynamic patching
feature"). Its unlikely we would ever apply these twice as they can't have a scope,
... and they all look safe.
Thanks,
James
next prev parent reply other threads:[~2018-09-18 17:47 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-28 15:51 [PATCH v5 00/27] arm64: provide pseudo NMI with GICv3 Julien Thierry
2018-08-28 15:51 ` [PATCH v5 01/27] arm64: cpufeature: Set SYSREG_GIC_CPUIF as a boot system feature Julien Thierry
2018-09-21 15:56 ` Marc Zyngier
[not found] ` <MWHPR0601MB3707D7CF3B55BF40EEEA0D52C4160@MWHPR0601MB3707.namprd06.prod.outlook.com>
2018-09-25 8:13 ` Marc Zyngier
2018-08-28 15:51 ` [PATCH v5 02/27] arm64: cpufeature: Use alternatives for VHE cpu_enable Julien Thierry
2018-09-12 10:28 ` James Morse
2018-09-12 12:03 ` Julien Thierry
2018-09-18 17:46 ` James Morse
2018-09-12 12:37 ` Suzuki K Poulose
2018-08-28 15:51 ` [PATCH v5 03/27] arm64: alternative: Apply alternatives early in boot process Julien Thierry
2018-09-12 10:29 ` James Morse
2018-09-12 16:49 ` Julien Thierry
2018-09-17 23:44 ` Daniel Thompson
2018-09-18 7:37 ` Julien Thierry
2018-09-18 17:47 ` James Morse [this message]
2018-09-21 16:05 ` Marc Zyngier
2018-08-28 15:51 ` [PATCH v5 04/27] arm64: daifflags: Use irqflags functions for daifflags Julien Thierry
2018-09-12 12:28 ` James Morse
2018-10-03 15:09 ` Catalin Marinas
2018-08-28 15:51 ` [PATCH v5 05/27] arm64: Use daifflag_restore after bp_hardening Julien Thierry
2018-09-12 10:32 ` James Morse
2018-09-12 11:11 ` Julien Thierry
2018-09-12 12:28 ` James Morse
2018-09-12 13:03 ` Julien Thierry
2018-10-03 15:12 ` Catalin Marinas
2018-08-28 15:51 ` [PATCH v5 06/27] arm64: Delay daif masking for user return Julien Thierry
2018-09-12 10:31 ` James Morse
2018-09-12 13:07 ` Julien Thierry
2018-08-28 15:51 ` [PATCH v5 07/27] arm64: xen: Use existing helper to check interrupt status Julien Thierry
2018-08-29 21:35 ` Stefano Stabellini
2018-10-03 15:14 ` Catalin Marinas
2018-08-28 15:51 ` [PATCH v5 08/27] irqchip/gic: Unify GIC priority definitions Julien Thierry
2018-10-03 9:24 ` Marc Zyngier
2018-08-28 15:51 ` [PATCH v5 09/27] irqchip/gic: Lower priority of GIC interrupts Julien Thierry
2018-08-28 15:51 ` [PATCH v5 10/27] arm64: cpufeature: Add cpufeature for IRQ priority masking Julien Thierry
2018-08-28 15:51 ` [PATCH v5 11/27] arm64: Make PMR part of task context Julien Thierry
2018-08-28 15:51 ` [PATCH v5 12/27] arm64: Unmask PMR before going idle Julien Thierry
2018-08-28 15:51 ` [PATCH v5 13/27] arm/arm64: gic-v3: Add helper functions to manage IRQ priorities Julien Thierry
2018-08-28 15:51 ` [PATCH v5 14/27] arm64: kvm: Unmask PMR before entering guest Julien Thierry
2018-08-28 15:51 ` [PATCH v5 15/27] arm64: irqflags: Use ICC_PMR_EL1 for interrupt masking Julien Thierry
2018-09-21 17:39 ` Julien Thierry
2018-09-21 17:55 ` Julien Thierry
2018-08-28 15:51 ` [PATCH v5 16/27] arm64: daifflags: Include PMR in daifflags restore operations Julien Thierry
2018-08-28 15:51 ` [PATCH v5 17/27] irqchip/gic-v3: Factor group0 detection into functions Julien Thierry
2018-08-28 15:51 ` [PATCH v5 18/27] irqchip/gic-v3: Do not overwrite PMR value Julien Thierry
2018-08-28 15:51 ` [PATCH v5 19/27] irqchip/gic-v3: Remove acknowledge loop Julien Thierry
2018-10-03 9:26 ` Marc Zyngier
2018-08-28 15:51 ` [PATCH v5 20/27] irqchip/gic-v3: Switch to PMR masking after IRQ acknowledge Julien Thierry
2018-08-28 15:51 ` [PATCH v5 21/27] arm64: Switch to PMR masking when starting CPUs Julien Thierry
2018-08-28 15:51 ` [PATCH v5 22/27] arm64: Add build option for IRQ masking via priority Julien Thierry
2018-08-28 15:51 ` [PATCH v5 23/27] arm64: Handle serror in NMI context Julien Thierry
2018-08-28 15:51 ` [PATCH v5 24/27] irqchip/gic-v3: Detect current view of GIC priorities Julien Thierry
2018-08-28 15:51 ` [PATCH v5 25/27] irqchip/gic-v3: Add base support for pseudo-NMI Julien Thierry
2018-08-28 15:51 ` [PATCH v5 26/27] irqchip/gic: Add functions to access irq priorities Julien Thierry
2018-08-28 15:51 ` [PATCH v5 27/27] irqchip/gic-v3: Allow interrupts to be set as pseudo-NMI Julien Thierry
2018-08-29 11:37 ` [PATCH v5 00/27] arm64: provide pseudo NMI with GICv3 Daniel Thompson
2018-08-29 12:58 ` Julien Thierry
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