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 601533C1F46 for ; Tue, 6 Oct 2026 08:53:33 +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=1791276815; cv=none; b=i56lFWSk6azv8Bl3ZkmhC8cP4Rj/QsdJtg15nUmCPYCQleU2sxAn+nVKbin4+yttxDsMxjegRKTZUhSGNs87NQ7cumumKFVOIorDGyZIVV1AqKiHXTJnhIrjINKRuSoP3rPzpVK/u94ysd7/igfIZiCxqtfHwDNvZYzpfobfUR0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791276815; c=relaxed/simple; bh=eRuW1QAwsDDC8Sd7sumLSr1tc0qtw8aRudbydE6NrSA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=NMHaYvbcyFmBQmbn0Pu9P76JV/KVe1X82gDsRBQJUn6dfVlkN0Excvuyx79KAKZB11UbrjKkIGIGLiqtAf3EFRy7oz474QDF1JY1eSQGppIQ1jtfvTF5BM7fCqWapMZmikBpbg4ucUaK6pfN1sn6Z2qTT2+aBoquezL3CiaIapA= 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; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=jwASbkxH; 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 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="jwASbkxH" 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 5DDB51516; Tue, 6 Oct 2026 01:53:29 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8FD593F86F; Tue, 6 Oct 2026 01:53:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1791276812; bh=eRuW1QAwsDDC8Sd7sumLSr1tc0qtw8aRudbydE6NrSA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=jwASbkxH7rZ+lWgRwyovlaSdag9mBPkbRFCzJBvWKYlwraIefI8PznT2J6+L+prjZ Z4/1id4WH+IJv4FIvVA4WP7xea+AE6c+XXsd6SFkr1jbIdzmcSfUg+gqJmZ8ocgemr 9DeJM+rSsqevai0P2Ad6DjHyqDNPTwivfbDlYK58= Date: Tue, 6 Oct 2026 10:53:28 +0200 From: Beata Michalska To: Sasha Levin Cc: stable@vger.kernel.org, Vladimir Murzin , Will Deacon Subject: Re: [PATCH 6.1.y] arm64: errata: Add Cortex-A725 erratum 3821522 workaround Message-ID: References: <2026100502-outtakes-dragonfly-ead9@gregkh> <20261006083052.3865406-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261006083052.3865406-1-sashal@kernel.org> This one is also missing/mixing things. Do let me know if you want me to make the backport. --- BR Beata On Tue, Oct 06, 2026 at 04:31:46AM -0400, Sasha Levin wrote: > From: Beata Michalska > > [ Upstream commit 45f7304679875eb000d67e194090ee7abd05c89c ] > > Cortex-A725 erratum 3821522 affects the CNT_CYCLES event, which can > incur a significant increment error when a CPU enters and subsequently > exits WFE or WFI, and may no longer track the system counter > frequency. > > The AMEVCNTR01_EL0 counter is used as the AMU constant counter for > frequency invariance and CPPC FFH feedback counters. Wire the affected > Cortex-A725 range into the shared broken AMU constant-counter capability > so the affected counter is treated as unavailable by returning zero in > the AMU counter paths. This prevents the broken counter from being used > as a reference source. > > The erratum can also affect PMUv3 users of the CNT_CYCLES event, > but this workaround intentionally does not change PMU event handling. > Hiding or rejecting the PMU event from the erratum code would change > the perf-visible PMU event interface, including raw event selection, > and would need a separate PMU-specific approach rather than being > folded into the AMU reference-counter workaround. > > Cc: stable@vger.kernel.org > Signed-off-by: Beata Michalska > Reviewed-by: Vladimir Murzin > Signed-off-by: Will Deacon > [ sashal: Reused ARM64_WORKAROUND_2457168 in place of the unavailable generic AMU capability. ] > Signed-off-by: Sasha Levin > --- > Documentation/arm64/silicon-errata.rst | 2 ++ > arch/arm64/Kconfig | 21 +++++++++++++++++++++ > arch/arm64/kernel/cpu_errata.c | 24 +++++++++++++++++++----- > arch/arm64/kernel/topology.c | 9 +++++---- > 4 files changed, 47 insertions(+), 9 deletions(-) > > diff --git a/Documentation/arm64/silicon-errata.rst b/Documentation/arm64/silicon-errata.rst > index fe7b90ac52d7b..74ae9e4f637a7 100644 > --- a/Documentation/arm64/silicon-errata.rst > +++ b/Documentation/arm64/silicon-errata.rst > @@ -155,6 +155,8 @@ stable kernels. > +----------------+-----------------+-----------------+-----------------------------+ > | ARM | Cortex-A725 | #3456106 | ARM64_ERRATUM_3194386 | > +----------------+-----------------+-----------------+-----------------------------+ > +| ARM | Cortex-A725 | #3821522 | ARM64_ERRATUM_3821522 | > ++----------------+-----------------+-----------------+-----------------------------+ > | ARM | Cortex-X1 | #3324344 | ARM64_ERRATUM_3194386 | > +----------------+-----------------+-----------------+-----------------------------+ > | ARM | Cortex-X1 | #4193791 | ARM64_ERRATUM_4118414 | > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 9cb8867eb1205..314a9ac22be54 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -983,6 +983,27 @@ config ARM64_ERRATUM_2457168 > > If unsure, say Y. > > +config ARM64_ERRATUM_3821522 > + bool "Cortex-A725: 3821522: workaround for possible CNT_CYCLES increment error due to WFE/WFI" > + depends on ARM64_AMU_EXTN > + default y > + help > + This option adds the workaround for ARM Cortex-A725 erratum 3821522. > + > + On affected A725 cores, the CNT_CYCLES event may incur a significant > + increment error when entering and subsequently exiting WFx. > + As a result, the CNT_CYCLES may diverge from the system counter > + frequency at which it is expected to increment. > + This renders the AMU counter AMEVCNTR01, that implements CNT_CYCLES, > + being unreliable and unsuitable for use. > + > + Since there is no hardware workaround, reads of the affected CNT_CYCLES > + counter return 0 in the relevant paths. This causes users of the counter > + to treat it as unavailable and is functionally equivalent to firmware > + disabling the affected counter. > + > + If unsure, say Y. > + > config ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD > bool > > diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c > index cff85a371c353..fbc80f64f3eeb 100644 > --- a/arch/arm64/kernel/cpu_errata.c > +++ b/arch/arm64/kernel/cpu_errata.c > @@ -275,6 +275,21 @@ static const struct arm64_cpu_capabilities arm64_repeat_tlbi_list[] = { > }; > #endif > > +#if defined(CONFIG_ARM64_ERRATUM_2457168) || \ > + defined(CONFIG_ARM64_ERRATUM_3821522) > +static const struct midr_range workaround_amu_constcnt_list[] = { > +#ifdef CONFIG_ARM64_ERRATUM_2457168 > + /* Cortex-A510 r0p0-r1p1 */ > + MIDR_RANGE(MIDR_CORTEX_A510, 0, 0, 1, 1), > +#endif > +#ifdef CONFIG_ARM64_ERRATUM_3821522 > + /* Cortex-A725 r0p0 - r0p2 */ > + MIDR_RANGE(MIDR_CORTEX_A725, 0, 0, 0, 2), > +#endif > + {} > +}; > +#endif > + > #ifdef CONFIG_CAVIUM_ERRATUM_23154 > static const struct midr_range cavium_erratum_23154_cpus[] = { > MIDR_ALL_VERSIONS(MIDR_THUNDERX), > @@ -737,14 +752,13 @@ const struct arm64_cpu_capabilities arm64_errata[] = { > ERRATA_MIDR_REV_RANGE(MIDR_CORTEX_A510, 0, 0, 2) > }, > #endif > -#ifdef CONFIG_ARM64_ERRATUM_2457168 > +#if defined(CONFIG_ARM64_ERRATUM_2457168) || \ > + defined(CONFIG_ARM64_ERRATUM_3821522) > { > - .desc = "ARM erratum 2457168", > + .desc = "Broken AMU AMEVCNTR01 (const counter)", > .capability = ARM64_WORKAROUND_2457168, > .type = ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE, > - > - /* Cortex-A510 r0p0-r1p1 */ > - CAP_MIDR_RANGE(MIDR_CORTEX_A510, 0, 0, 1, 1) > + CAP_MIDR_RANGE_LIST(workaround_amu_constcnt_list) > }, > #endif > #ifdef CONFIG_ARM64_ERRATUM_2038923 > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c > index 817d788cd8666..575d0f9a76870 100644 > --- a/arch/arm64/kernel/topology.c > +++ b/arch/arm64/kernel/topology.c > @@ -268,10 +268,11 @@ static void cpu_read_corecnt(void *val) > static void cpu_read_constcnt(void *val) > { > /* > - * Return 0 if the current CPU is affected by erratum 2457168. A value > - * of 0 is also returned if the current CPU does not support AMUs or if > - * the counter is disabled. A return value of 0 at counter read is > - * properly handled as an error case by the users of the counter. > + * Return 0 if the current CPU is affected by a HW erratum. > + * A value of 0 is also returned if the current CPU does not > + * support AMUs or if the counter is disabled. A return > + * value of 0 at counter read is properly handled as an error > + * case by the users of the counter. > */ > *(u64 *)val = this_cpu_has_cap(ARM64_WORKAROUND_2457168) ? > 0UL : read_constcnt(); > -- > 2.53.0 >