Re: [PATCH v3 09/21] arm64: cpufeature: Add global feature override facility
From: Catalin Marinas <catalin.marinas@arm.com>
Date: 2021-01-11 18:42:58
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Hi Marc, On Mon, Jan 11, 2021 at 01:27:59PM +0000, Marc Zyngier wrote:
Add a facility to globally override a feature, no matter what the HW says. Yes, this is dangerous.
Yeah, it's dangerous. We can make it less so if we only allow safe values (e.g. lower if FTR_UNSIGNED).
quoted hunk ↗ jump to hunk
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h index 9a555809b89c..465d2cb63bfc 100644 --- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h@@ -75,6 +75,8 @@ struct arm64_ftr_reg { u64 sys_val; u64 user_val; const struct arm64_ftr_bits *ftr_bits; + u64 *override_val; + u64 *override_mask; };
At the arm64_ftr_reg level, we don't have any information about the safe values for a feature. Could we instead move this to arm64_ftr_bits? We probably only need a single field. When populating the feature values, we can make sure it doesn't go above the hardware one. I attempted a feature modification for MTE here, though I dropped the entire series in the meantime as we clarified the ARM ARM: https://lore.kernel.org/linux-arm-kernel/20200515171612.1020-24-catalin.marinas@arm.com/ (local) Srinivas copied it in his patch (but forgot to give credit ;)): https://lore.kernel.org/linux-arm-msm/1610152163-16554-3-git-send-email-sramana@codeaurora.org/ (local) The above adds a filter function but, instead, just use your mechanism in this series for idreg.feature setting via cmdline. The arm64_ftr_value() function extracts the hardware value and lowers it if a cmdline argument was passed. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel