From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751393AbeEDKHC (ORCPT ); Fri, 4 May 2018 06:07:02 -0400 Received: from foss.arm.com ([217.140.101.70]:51792 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751196AbeEDKHA (ORCPT ); Fri, 4 May 2018 06:07:00 -0400 Subject: Re: [PATCH v2 2/6] arm64: alternative: Apply alternatives early in boot process To: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: mark.rutland@arm.com, marc.zyngier@arm.com, james.morse@arm.com, daniel.thompson@linaro.org, Catalin Marinas , Will Deacon , Suzuki K Poulose References: <1516190084-18978-1-git-send-email-julien.thierry@arm.com> <1516190084-18978-3-git-send-email-julien.thierry@arm.com> From: Julien Thierry Message-ID: Date: Fri, 4 May 2018 11:06:56 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <1516190084-18978-3-git-send-email-julien.thierry@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, In order to prepare the v3 of this patchset, I'd like people's opinion on what this patch does. More below. On 17/01/18 11:54, Julien Thierry wrote: > From: Daniel Thompson > > Currently alternatives are applied very late in the boot process (and > a long time after we enable scheduling). Some alternative sequences, > such as those that alter the way CPU context is stored, must be applied > much earlier in the boot sequence. > > Introduce apply_alternatives_early() to allow some alternatives to be > applied immediately after we detect the CPU features of the boot CPU. > > Signed-off-by: Daniel Thompson > Signed-off-by: Julien Thierry > Cc: Catalin Marinas > Cc: Will Deacon > --- > arch/arm64/include/asm/alternative.h | 1 + > arch/arm64/kernel/alternative.c | 39 +++++++++++++++++++++++++++++++++--- > arch/arm64/kernel/smp.c | 6 ++++++ > 3 files changed, 43 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h > index 4a85c69..1fc1cdb 100644 > --- a/arch/arm64/include/asm/alternative.h > +++ b/arch/arm64/include/asm/alternative.h > @@ -20,6 +20,7 @@ struct alt_instr { > u8 alt_len; /* size of new instruction(s), <= orig_len */ > }; > > +void __init apply_alternatives_early(void); > void __init apply_alternatives_all(void); > void apply_alternatives(void *start, size_t length); > > diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c > index 6dd0a3a3..78051d4 100644 > --- a/arch/arm64/kernel/alternative.c > +++ b/arch/arm64/kernel/alternative.c > @@ -28,6 +28,18 @@ > #include > #include > > +/* > + * early-apply features are detected using only the boot CPU and checked on > + * secondary CPUs startup, even then, > + * These early-apply features should only include features where we must > + * patch the kernel very early in the boot process. > + * > + * Note that the cpufeature logic *must* be made aware of early-apply > + * features to ensure they are reported as enabled without waiting > + * for other CPUs to boot. > + */ > +#define EARLY_APPLY_FEATURE_MASK BIT(ARM64_HAS_SYSREG_GIC_CPUIF) > + Following the change in the cpufeature infrastructure, ARM64_HAS_SYSREG_GIC_CPUIF will have the scope ARM64_CPUCAP_SCOPE_BOOT_CPU in order to be checked early in the boot process. Now, regarding the early application of alternative, I am wondering whether we can apply all the alternatives associated with SCOPE_BOOT features that *do not* have a cpu_enable callback. Otherwise we can keep the macro to list individually each feature that is patchable at boot time as the current patch does (or put this info in a flag within the arm64_cpu_capabilities structure). Any thoughts or preferences on this? Thanks, > #define __ALT_PTR(a,f) ((void *)&(a)->f + (a)->f) > #define ALT_ORIG_PTR(a) __ALT_PTR(a, orig_offset) > #define ALT_REPL_PTR(a) __ALT_PTR(a, alt_offset) > @@ -105,7 +117,8 @@ static u32 get_alt_insn(struct alt_instr *alt, __le32 *insnptr, __le32 *altinsnp > return insn; > } > > -static void __apply_alternatives(void *alt_region, bool use_linear_alias) > +static void __apply_alternatives(void *alt_region, bool use_linear_alias, > + unsigned long feature_mask) > { > struct alt_instr *alt; > struct alt_region *region = alt_region; > @@ -115,6 +128,9 @@ static void __apply_alternatives(void *alt_region, bool use_linear_alias) > u32 insn; > int i, nr_inst; > > + if ((BIT(alt->cpufeature) & feature_mask) == 0) > + continue; > + > if (!cpus_have_cap(alt->cpufeature)) > continue; > > @@ -138,6 +154,21 @@ static void __apply_alternatives(void *alt_region, bool use_linear_alias) > } > > /* > + * This is called very early in the boot process (directly after we run > + * a feature detect on the boot CPU). No need to worry about other CPUs > + * here. > + */ > +void apply_alternatives_early(void) > +{ > + struct alt_region region = { > + .begin = (struct alt_instr *)__alt_instructions, > + .end = (struct alt_instr *)__alt_instructions_end, > + }; > + > + __apply_alternatives(®ion, true, EARLY_APPLY_FEATURE_MASK); > +} > + > +/* > * We might be patching the stop_machine state machine, so implement a > * really simple polling protocol here. > */ > @@ -156,7 +187,9 @@ static int __apply_alternatives_multi_stop(void *unused) > isb(); > } else { > BUG_ON(patched); > - __apply_alternatives(®ion, true); > + > + __apply_alternatives(®ion, true, ~EARLY_APPLY_FEATURE_MASK); > + > /* Barriers provided by the cache flushing */ > WRITE_ONCE(patched, 1); > } > @@ -177,5 +210,5 @@ void apply_alternatives(void *start, size_t length) > .end = start + length, > }; > > - __apply_alternatives(®ion, false); > + __apply_alternatives(®ion, false, -1); > } > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c > index 551eb07..37361b5 100644 > --- a/arch/arm64/kernel/smp.c > +++ b/arch/arm64/kernel/smp.c > @@ -453,6 +453,12 @@ void __init smp_prepare_boot_cpu(void) > * cpuinfo_store_boot_cpu() above. > */ > update_cpu_errata_workarounds(); > + /* > + * We now know enough about the boot CPU to apply the > + * alternatives that cannot wait until interrupt handling > + * and/or scheduling is enabled. > + */ > + apply_alternatives_early(); > } > > static u64 __init of_get_cpu_mpidr(struct device_node *dn) > -- > 1.9.1 > -- Julien Thierry