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 568013BFE2F for ; Tue, 6 Oct 2026 08:47:50 +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=1791276472; cv=none; b=ZOxz9XjFPSv1E/xYkEXrsbTw921PZubCODl0vTwLKZiq1eVYTSOKCOAf29c1+SINN0M3VCZolSXWj+sfLGOSw/QofYcgUO1ZTY/BD9HRY6+7PlhiAzVXMI5Mty4eChEWP9RhShN3J4N1uwO1ZuFkdz50mkstSjk5pN7zB/MN2fQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791276472; c=relaxed/simple; bh=jAFp60YdOP/+i3TbS54DclPF8l/52EgJtbYNs9xW19Y=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=f4qGAlzxmK8ruEnpOgGbH3E/mufnevFjNkstTcwa6DlK4c/NuHzCXK/QK4W+DEiozxC7MV1h1DYO6ZVaT/PqwyWE2JWFqTM48Ttu+7ireLOSglyFnyFrB9ol7nDHQnfYGaaILXFabR6cok7geshHh2TBwesOP3Ti69vN9wbJPlw= 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=I9X/OoiS; 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="I9X/OoiS" 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 25CA71516; Tue, 6 Oct 2026 01:47:46 -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 51B373F86F; Tue, 6 Oct 2026 01:47:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1791276469; bh=jAFp60YdOP/+i3TbS54DclPF8l/52EgJtbYNs9xW19Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=I9X/OoiSov91WrpSHABoJ3NKjfBPWLBQutbypVF5Eh5xmHHjuU8mvBi8eQjb8t+np wyVHW1Gj9UBNd/wtjnBKq/C/KbeOsD6RyuC9ujM290Gq11KPRrIMGLrePHgDlPpFjf TW7jALcDH0d668OG8uxWr/YFnDlTqot5uMGrJL+0= Date: Tue, 6 Oct 2026 10:47:45 +0200 From: Beata Michalska To: Sasha Levin Cc: stable@vger.kernel.org, Vladimir Murzin , Will Deacon Subject: Re: [PATCH 6.18.y 2/2] arm64: errata: Add Cortex-A725 erratum 3821522 workaround Message-ID: References: <2026100500-elsewhere-excretion-642e@gregkh> <20261006000910.3554634-1-sashal@kernel.org> <20261006000910.3554634-2-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: <20261006000910.3554634-2-sashal@kernel.org> LGTM. Thank you. --- BR Beata On Mon, Oct 05, 2026 at 08:09:27PM -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 > Signed-off-by: Sasha Levin > --- > 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(-) > > diff --git a/Documentation/arch/arm64/silicon-errata.rst b/Documentation/arch/arm64/silicon-errata.rst > index 1c5accd6dec49..75c6ba532c20c 100644 > --- 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 | > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 8f483df09dbe7..2e567a7d89c9b 100644 > --- 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 > > diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c > index 917231415c007..516a1e37a51fe 100644 > --- a/arch/arm64/kernel/cpu_errata.c > +++ b/arch/arm64/kernel/cpu_errata.c > @@ -358,6 +358,10 @@ 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 > {} > }; > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c > index 6ad8ea3c7258b..202f677e2b0f2 100644 > --- 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(); > -- > 2.53.0 >