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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Jan 17, 2020 at 04:13:06PM +0530, Amit Kachhap wrote: > On 1/16/20 9:54 PM, Catalin Marinas wrote: > > On Mon, Dec 16, 2019 at 02:17:08PM +0530, Amit Daniel Kachhap wrote: > > > diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S > > > index 5aaf1bb..c59c28f 100644 > > > --- a/arch/arm64/kernel/head.S > > > +++ b/arch/arm64/kernel/head.S [...] > > > +ENTRY(__cpu_secondary_checkptrauth) > > > +#ifdef CONFIG_ARM64_PTR_AUTH > > > + /* Check if the CPU supports ptrauth */ > > > + mrs x2, id_aa64isar1_el1 > > > + ubfx x2, x2, #ID_AA64ISAR1_APA_SHIFT, #8 > > > + cbnz x2, 1f > > > +alternative_if ARM64_HAS_ADDRESS_AUTH > > > + mov x3, 1 > > > +alternative_else > > > + mov x3, 0 > > > +alternative_endif > > > + cbz x3, 1f > > > + /* Park the mismatched secondary CPU */ > > > + early_park_cpu CPU_STUCK_REASON_NO_PTRAUTH > > > +#endif > > > +1: ret > > > +ENDPROC(__cpu_secondary_checkptrauth) > > > > Do we actually need to park secondary CPUs early? Let's say a secondary > > CPU doesn't have PAC, __cpu_setup won't set the corresponding SCTLR_EL1 > > bits and the instructions are NOPs. Wouldn't the cpufeature framework > > park it later anyway? > > In the current cpufeature framework, such missing cpufeature in > secondary cpu will lead to kernel panic (inside check_early_cpufeatures) > and not cpu offline. However Kristina in her RFC V2 [1] added such > feature to park it. I remember discussing how to avoid the kernel panic with her at the time. > Later for moving the enabling ptrauth to assembly this work got dropped. > Suzuki provided the template code for doing that [2]. > > Later James suggested to do this like existing > __cpu_secondary_check52bitva which parks the secondary cpu very early > and also to save wasted cpu cycles [3]. I don't really care about a few cycles lost during boot. > So your question is still valid that it can be done in cpufeature. Let > me know your opinion that which one is better. My preference is for Kristina's approach. The 52-bit VA is slightly different (as is VHE) as we cannot guarantee the secondary CPU to even reach the CPU framework. With PAC, I don't see why it would fail reaching the C code, so I'd prefer a more readable C implementation than the assembler one. Anyway, I'm open to counterarguments here. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel