From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 52B84109C04A for ; Wed, 25 Mar 2026 17:51:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Ky4DvPbbgbPbz/fiQ3c/eRMLtH5FjLUEf7wNWkzqAPI=; b=JQZ5IIKCSn7tmrKlmQfFHp8iqQ jjd5Ldm2eUfuAtGoCMkH6m0WnBy1IqGFo2WWnCBFIPnRittjHnfzKlgdV8i9ApTQaVYL+Y6gnYYNc D7vMrsGkSHeXf3jkBLJFVbWcHls80e8OPCxyMm5GQ1T6sGe5gU8NqKqLGVvX4f2zTSM2pSIogZFju vax63pNHd0FNJ26r12/8QWWG1ME3VC/43oIWcz1pt2ApWWd4m08qWZgf9HomrWrR6FyfLxXqMsnoR GPPViL/1cSj1l7buP5lGwSrS+0Nrbq+OG5xxgIVZshGuFJu8AtlchjduNX2ng0fdo2y6YyVRYbGl1 /7PaSFmw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1w5SOR-000000041F0-3bly; Wed, 25 Mar 2026 17:51:47 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1w5SOP-000000041EG-0P3y for linux-arm-kernel@lists.infradead.org; Wed, 25 Mar 2026 17:51:46 +0000 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 2E0E92444; Wed, 25 Mar 2026 10:51:38 -0700 (PDT) Received: from arm.com (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CC8033F836; Wed, 25 Mar 2026 10:51:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1774461104; bh=eyHFdRn6lnnq6+lCvCionMA4Nb++tb101R0MsbqPO8w=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=uzw9nsMrAWynoJtFLpCa/TUcYX/0f9tskJXQBeSJ+HaO/oOxxij0klbRy1ONBXGnE Ewv0m9zqd7e9lcNBYGd7L/pESkasEwZrYk4zx68dv4N/cY5upC/HsEvFU218WccCqq qWtbgxCz292RMALQFQs+nea5dMsRCAVoRbn8pbBo= Date: Wed, 25 Mar 2026 17:51:39 +0000 From: Catalin Marinas To: Suzuki K Poulose Cc: Marc Zyngier , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, Fuad Tabba , Will Deacon , Mark Rutland , Joey Gouly , Oliver Upton , Zenghui Yu Subject: Re: [PATCH v2 01/11] arm64: Skip update of an idreg field affected by an override Message-ID: References: <20260302115653.1517326-1-maz@kernel.org> <20260302115653.1517326-2-maz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260325_105145_449055_D9F34E9F X-CRM114-Status: GOOD ( 35.18 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Mar 25, 2026 at 02:54:28PM +0000, Suzuki K Poulose wrote: > On 19/03/2026 15:34, Catalin Marinas wrote: > > On Mon, Mar 02, 2026 at 11:56:42AM +0000, Marc Zyngier wrote: > > > When computing the new value od an idreg that contains a field > > > affected by an override, do not update that particular field. > > > > > > The value computed at init-time must be kept as-is, as that's > > > what the user has asked for, for better or worse. > > > > > > Signed-off-by: Marc Zyngier > > > --- > > > arch/arm64/kernel/cpufeature.c | 7 +++++++ > > > 1 file changed, 7 insertions(+) > > > > > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > > > index c31f8e17732a3..28fc77443ccd3 100644 > > > --- a/arch/arm64/kernel/cpufeature.c > > > +++ b/arch/arm64/kernel/cpufeature.c > > > @@ -1224,6 +1224,13 @@ static void update_cpu_ftr_reg(struct arm64_ftr_reg *reg, u64 new) > > > s64 ftr_cur = arm64_ftr_value(ftrp, reg->sys_val); > > > s64 ftr_new = arm64_ftr_value(ftrp, new); > > > + /* > > > + * Don't alter the initial value that has been forced > > > + * by an override. > > > + */ > > > + if ((reg->override->mask & arm64_ftr_mask(ftrp)) == arm64_ftr_mask(ftrp)) > > > + continue; > > > > I got lost in the in the cpufeature framework, so I may be missing > > something. > > > > Let's say the primary CPU has a feature field with value 2 and we want > > to override it to value 1. For e.g. a LOWER_SAFE feature, boot_cpu_data > > will stored the overridden value of 1. > > > > A secondary CPU comes online with the same feature missing, so value 0. > > With the above change, we no longer update the system-wide feature > > value, leave it as 1. Later on, for a system feature we may turn it on > > even though the secondary CPU does not support it. > > > > In summary, this makes the overridden field sticky for secondary CPUs > > even if they don't support it. > > That is true. I think we should let the secondary CPUs alter the values, > with initial CPU feature value with the override value set, the system > could then choose the safest among the override and the others. It works for me. We should add a comment somewhere that the override is not expected to work for features where we allow differences (some FTR_NONSTRICT). > > Unrelated to your patch, I think we can similarly fail to reject > > secondary CPUs in check_early_cpu_features() -> verify_local_cpu_caps() > > because of __read_sysreg_by_encoding() which uses the override value > > unconditionally. From this perspective, we are now consistent with your > > patch above. > > This is true as well and the override takes the priority and with the > wrong level of override value the system could be made to think that > some features are available even when it is unsafe to do so. > We should sanitise the values read by __read_sysreg_by_encoding() with > the "overrides". I can cook something up. Or remove this check if we expect the override to only work on the resulting sanitised value, not individual checks. -- Catalin