From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 35A121C07D9; Fri, 14 Mar 2025 09:27:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741944423; cv=none; b=jPfRFdUEsBpJ1gThwHW1uVfDdAAdnndZ2J9VCTlQoh98wzkre4ywgQlI0pfXOe0LR40wkvSQL1p3MIBuVYmhtYrDAJR7MR3p5MI8BqBEyoo9dwtxRMjOL5VaIgGjUkc3LIehWHPMHMvHLoO/RelYxrWmZK2bpK7AsZxL/0hwCg8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741944423; c=relaxed/simple; bh=JcldlY/ETPmR3IenknhNxPNgRcWA0ROHMHWWITDho/I=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=BqtDtBIi8pw7nja+MEluEiSLuSWQoEw7Sb1w/8jK4z9ZIo5h4UwKZPNr/sUMrjMlhTa/6cDhu6VLnpsC4eB5UXpIkLOnJ8pnW+TpyMBtx11f+J7WFYeuFsO72ywSeNlFsyu7NlHTPonOkLn1cXtsQsTO+C6LMOeRsIecR8vXz5c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 549631424; Fri, 14 Mar 2025 02:27:11 -0700 (PDT) Received: from [10.57.85.159] (unknown [10.57.85.159]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 73EA03F673; Fri, 14 Mar 2025 02:26:57 -0700 (PDT) Message-ID: Date: Fri, 14 Mar 2025 09:26:56 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/3] arm64: Add BBM Level 2 cpu feature Content-Language: en-GB To: =?UTF-8?Q?Miko=C5=82aj_Lenczewski?= Cc: suzuki.poulose@arm.com, yang@os.amperecomputing.com, corbet@lwn.net, catalin.marinas@arm.com, will@kernel.org, jean-philippe@linaro.org, robin.murphy@arm.com, joro@8bytes.org, akpm@linux-foundation.org, mark.rutland@arm.com, joey.gouly@arm.com, maz@kernel.org, james.morse@arm.com, broonie@kernel.org, anshuman.khandual@arm.com, oliver.upton@linux.dev, ioworker0@gmail.com, baohua@kernel.org, david@redhat.com, jgg@ziepe.ca, shameerali.kolothum.thodi@huawei.com, nicolinc@nvidia.com, mshavit@google.com, jsnitsel@redhat.com, smostafa@google.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev References: <20250313104111.24196-2-miko.lenczewski@arm.com> <20250313104111.24196-3-miko.lenczewski@arm.com> <20250313180833.GA40525@mazurka.cambridge.arm.com> From: Ryan Roberts In-Reply-To: <20250313180833.GA40525@mazurka.cambridge.arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 13/03/2025 18:08, Mikołaj Lenczewski wrote: > On Thu, Mar 13, 2025 at 04:13:22PM +0000, Ryan Roberts wrote: >> On 13/03/2025 10:41, Mikołaj Lenczewski wrote: >>> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c >>> index d561cf3b8ac7..b936e0805161 100644 >>> --- a/arch/arm64/kernel/cpufeature.c >>> +++ b/arch/arm64/kernel/cpufeature.c >>> @@ -2176,6 +2176,76 @@ static bool hvhe_possible(const struct arm64_cpu_capabilities *entry, >>> return arm64_test_sw_feature_override(ARM64_SW_FEATURE_OVERRIDE_HVHE); >>> } >>> >>> +static inline bool bbml2_possible(void) >>> +{ >>> + return !arm64_test_sw_feature_override(ARM64_SW_FEATURE_OVERRIDE_NOBBML2); >> >> If you're going to keep this helper, I think it really needs to be: >> >> return IS_ENABLED(CONFIG_ARM64_BBML2_NOABORT) && >> !arm64_test_sw_feature_override(ARM64_SW_FEATURE_OVERRIDE_NOBBML2); >> >> Then you would simplify the caller to remove it's own >> IS_ENABLED(CONFIG_ARM64_BBML2_NOABORT) check. >> >> But personally I would remove the helper and just fold the test into >> has_bbml2_noabort(). >> >> Thanks, >> Ryan > > I was debating folding it into has_bbml2_noabort(), but went ahead and > implemented it separately to match hvhe_possible(), which was another sw > feature helper. hvhe_possible() is a .matches function, so there is nothing to fold it into. > > But I agree, folding it will be simpler and read just as easily (if not > easier). Will do so. > >>> +} >>> + >>> +static bool cpu_has_bbml2_noabort(unsigned int cpu_midr) >>> +{ >>> + /* We want to allow usage of bbml2 in as wide a range of kernel contexts >>> + * as possible. This list is therefore an allow-list of known-good >>> + * implementations that both support bbml2 and additionally, fulfill the >>> + * extra constraint of never generating TLB conflict aborts when using >>> + * the relaxed bbml2 semantics (such aborts make use of bbml2 in certain >>> + * kernel contexts difficult to prove safe against recursive aborts). >>> + * >>> + * Note that implementations can only be considered "known-good" if their >>> + * implementors attest to the fact that the implementation never raises >>> + * TLBI conflict aborts for bbml2 mapping granularity changes. >>> + */ >>> + static const struct midr_range supports_bbml2_noabort_list[] = { >>> + MIDR_REV_RANGE(MIDR_CORTEX_X4, 0, 3, 0xf), >>> + MIDR_REV_RANGE(MIDR_NEOVERSE_V3, 0, 2, 0xf), >>> + {} >>> + }; >>> + >>> + return is_midr_in_range_list(cpu_midr, supports_bbml2_noabort_list); >>> +} >>> + >>> +static inline unsigned int __cpu_read_midr(int cpu) >> >> nit: why the double underscrore prefix? > > Again copying other helpers I saw that seemed to do similar things. > Didn't know if this was the expected style, so did as other helpers did. > Will remove. Often those double underscores are used when you have a public function wrapping into a private function, like this: static void __do_a_thing(bool modify_behaviour_in_some_way); void do_a_thing(void) { __do_a_thing(false); } I'm sure the coding style offers a better explanation. Thanks, Ryan > > Thank you for the review. >