From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 ADA064E4C4B; Fri, 9 Oct 2026 14:49:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791557356; cv=none; b=NdLLOFvJSxTz/2qAcrRKtSOBYLFCR+yZEDcWv/sg7MUhNfDbt4uxkqj/1o+f07LtpmM9XiZqCJCc547gHKGgI5E2w5j7pQh6hX9ev5FCeI44sNHTLdkq+9J1GUdQ7xaw4ni8u26x/pBHV3vDcT1cNR4TDVE0Fk6zWBFYaC1YnsE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791557356; c=relaxed/simple; bh=Kj+peeWrxwp+r8GKcxltvCRGEtZxrnHdo+FBsMlbYUo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=l7kHGZZvUbgqqmRkkAufbMX2e+XByDNdqd3eUKHxm09cycTZHAy67McJABAw/4sRV89A38OVwpb/WP9wDculIOdt3lgzjWYlhGS0u9LxPux3wBIH0F6nCsPMh9LRQYwe4UTafWZl/1/No6YGvQepawsrT3Dt6kac8qjgilnTyrc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=hSUzM/nC; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="hSUzM/nC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 173BD1F000FF; Fri, 9 Oct 2026 14:49:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1791557355; bh=7ub/VGEZAH9t75IlkoG9Ulolx0BXRGhi2J0Ds5O21V4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=hSUzM/nChbymD8/0nMhwvffEy1exOMccg/QvENN7UY+5oGPr4S2Aa03Shw8gjRUTK OKJgahmjaKTOc6v9wuZAPL/9idqS2zPqoEFZL/0DZBjVOTfPjhQY3/iJ03KBsEzfe2 kT6rxOXf0lZm21OVKBNZ+GgbLkpSDKBVEvYMUYYc= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Beata Michalska , Vladimir Murzin , Will Deacon , Sasha Levin Subject: [PATCH 6.18 387/403] arm64: errata: Add Cortex-A725 erratum 3821522 workaround Date: Fri, 9 Oct 2026 16:12:28 +0200 Message-ID: <20261009141001.388400986@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261009140952.119038291@linuxfoundation.org> References: <20261009140952.119038291@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ 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 Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- Documentation/arch/arm64/silicon-errata.rst | 2 ++ arch/arm64/Kconfig | 22 ++++++++++++++++++++++ arch/arm64/kernel/cpu_errata.c | 4 ++++ arch/arm64/kernel/topology.c | 9 +++++---- 4 files changed, 33 insertions(+), 4 deletions(-) --- a/Documentation/arch/arm64/silicon-errata.rst +++ b/Documentation/arch/arm64/silicon-errata.rst @@ -168,6 +168,8 @@ stable kernels. +----------------+-----------------+-----------------+-----------------------------+ | ARM | Cortex-A725 | #3456106 | ARM64_ERRATUM_3194386 | +----------------+-----------------+-----------------+-----------------------------+ +| ARM | Cortex-A725 | #3821522 | ARM64_ERRATUM_3821522 | ++----------------+-----------------+-----------------+-----------------------------+ | ARM | Cortex-X1 | #1502854 | N/A | +----------------+-----------------+-----------------+-----------------------------+ | ARM | Cortex-X1 | #3324344 | ARM64_ERRATUM_3194386 | --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -1090,6 +1090,28 @@ config ARM64_ERRATUM_2645198 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 + select ARM64_WORKAROUND_BROKEN_AMU_CONSTCNT + 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 --- a/arch/arm64/kernel/cpu_errata.c +++ b/arch/arm64/kernel/cpu_errata.c @@ -359,6 +359,10 @@ static const struct midr_range workaroun /* 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 /* CONFIG_ARM64_WORKAROUND_BROKEN_AMU_CONSTCNT */ --- a/arch/arm64/kernel/topology.c +++ b/arch/arm64/kernel/topology.c @@ -426,10 +426,11 @@ 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_BROKEN_AMU_CONSTCNT) ? 0UL : read_constcnt();