From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 30F2E220689; Thu, 19 Jun 2025 11:05:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750331112; cv=none; b=OwJJLcoPD7ShzzChdKT69hQ+NkoFP2XRbHNymOlI03BjZRYTS5SOD7SXlvHxCiGawIbkV1oQ1NuXcj69TPPuzCO/3t66h2bhhng3+QonZKE6RYoslxvYE3K1Wklr3joz0WQZsI7vb+Yic+FUd4mYLI581+fxabVXAIuMf8Rly+0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750331112; c=relaxed/simple; bh=rYhliljQfdXy0EYM3FNValqPiZeolZqxBnCCabM44Cs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QbSDDlWHmQbdnCpfEnYtIc4xsGprD8X/3Cu3+a4C0zfxPNrM3OyyvtxX7Xd5wZsUowtEc9iFGSpkAercEEgHH5Sgs5QRISmURuqFcrJx9gtUHKNhXWW5j0Luo4Js8eKdEzjv0vkDKBW2ans73Ar0STIVoYwzukNhel0XvAO/v/I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id BF159C4CEEA; Thu, 19 Jun 2025 11:05:07 +0000 (UTC) Date: Thu, 19 Jun 2025 12:05:05 +0100 From: Catalin Marinas To: =?utf-8?Q?Miko=C5=82aj?= Lenczewski Cc: ryan.roberts@arm.com, yang@os.amperecomputing.com, will@kernel.org, jean-philippe@linaro.org, robin.murphy@arm.com, joro@8bytes.org, maz@kernel.org, oliver.upton@linux.dev, joey.gouly@arm.com, james.morse@arm.com, broonie@kernel.org, ardb@kernel.org, baohua@kernel.org, suzuki.poulose@arm.com, david@redhat.com, jgg@ziepe.ca, nicolinc@nvidia.com, jsnitsel@redhat.com, mshavit@google.com, kevin.tian@intel.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, iommu@lists.linux.dev Subject: Re: [PATCH v7 2/4] arm64: Add BBM Level 2 cpu feature Message-ID: References: <20250617095104.6772-1-miko.lenczewski@arm.com> <20250617095104.6772-3-miko.lenczewski@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250617095104.6772-3-miko.lenczewski@arm.com> On Tue, Jun 17, 2025 at 09:51:02AM +0000, MikoĊ‚aj Lenczewski wrote: > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > index f9c947166322..2e80ff237b96 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -2213,6 +2213,41 @@ static bool hvhe_possible(const struct arm64_cpu_capabilities *entry, > return arm64_test_sw_feature_override(ARM64_SW_FEATURE_OVERRIDE_HVHE); > } > > +static bool has_bbml2_noabort(const struct arm64_cpu_capabilities *caps, int scope) > +{ > + /* > + * 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. s/TLBI/TLB/ > + */ > + 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), > + {} > + }; > + > + /* Does our cpu guarantee to never raise TLB conflict aborts? */ > + if (!is_midr_in_range_list(supports_bbml2_noabort_list)) > + return false; > + > + /* > + * We currently ignore the AA64_ID_MMFR2 register, and only care about s/AA64_ID_MMFR2/ID_AA64MMFR2_EL1/ > + * whether the MIDR check passes. This is because we specifically > + * care only about a stricter form of BBML2 (one guaranteeing noabort), > + * and so the MMFR2 check is pointless (all implementations passing the > + * MIDR check should also pass the MMFR2 check). I think there's at least one implementation that behaves as BBML2-noabort but does not have the ID field advertising BBML2. > + */ > + > + return true; > +} > + > #ifdef CONFIG_ARM64_PAN > static void cpu_enable_pan(const struct arm64_cpu_capabilities *__unused) > { > @@ -2980,6 +3015,11 @@ static const struct arm64_cpu_capabilities arm64_features[] = { > .matches = has_cpuid_feature, > ARM64_CPUID_FIELDS(ID_AA64MMFR2_EL1, EVT, IMP) > }, > + { > + .capability = ARM64_HAS_BBML2_NOABORT, > + .type = ARM64_CPUCAP_EARLY_LOCAL_CPU_FEATURE, > + .matches = has_bbml2_noabort, > + }, > { > .desc = "52-bit Virtual Addressing for KVM (LPA2)", > .capability = ARM64_HAS_LPA2, > diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps > index 10effd4cff6b..2bd2bfaeddcd 100644 > --- a/arch/arm64/tools/cpucaps > +++ b/arch/arm64/tools/cpucaps > @@ -45,6 +45,7 @@ HAS_LPA2 > HAS_LSE_ATOMICS > HAS_MOPS > HAS_NESTED_VIRT > +HAS_BBML2_NOABORT > HAS_PAN > HAS_PMUV3 > HAS_S1PIE Otherwise it looks fine. Reviewed-by: Catalin Marinas