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 9CF902586DD for ; Tue, 11 Feb 2025 11:35:10 +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=1739273713; cv=none; b=Gs/PdWPau/simXlMrPBs3UA7yb+EKzsaP4zm/MxN8njqNOLIfviWPS9zRp3twBNoKxKHFg2afFSiC+gBiJtiAEaljKo6zGwfSggbDQxUS3Heqbh+KqAUCCMZ1UQCknC2YclZN5gBubhKNWQdjJtOTcPvQllWYAUHQ9usN0bodEg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739273713; c=relaxed/simple; bh=xcBYWHeQFRNWxiLoR5K9RpPqhW8/hq4zAlf+CCKVN6I=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=otV79nrL9WG3auMhZVnyXeEPjGT8Zh8SjouYU+vjKS8IjERDoRLs2x9DpR7mF7FX+Uo2hf6mTEX7Fx6AG719YPNk860xF/1GrCf3gGM5HSVv+OqXiuJnAKXDewmQpJCK0umgBuxvALyX4TwwGhcxZP0ncgZxNF9T40sqcH61as0= 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; 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 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 770D21424; Tue, 11 Feb 2025 03:35:31 -0800 (PST) Received: from J2N7QTR9R3 (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 546A73F5A1; Tue, 11 Feb 2025 03:35:08 -0800 (PST) Date: Tue, 11 Feb 2025 11:34:57 +0000 From: Mark Rutland To: Mark Brown Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, Fuad Tabba , Marc Zyngier , Oliver Upton , James Morse , Suzuki K Poulose , Catalin Marinas , Will Deacon Subject: Re: [PATCH v6] KVM: arm64: Fix confusion in documentation for pKVM SME assert Message-ID: References: <20250210-kvm-arm64-sme-assert-v6-1-cc26c46d1b43@kernel.org> 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=us-ascii Content-Disposition: inline In-Reply-To: <20250210-kvm-arm64-sme-assert-v6-1-cc26c46d1b43@kernel.org> On Mon, Feb 10, 2025 at 09:33:32PM +0000, Mark Brown wrote: > As raised in the review comments for the original patch the assert and > comment added in afb91f5f8ad7 ("KVM: arm64: Ensure that SME controls are > disabled in protected mode") are bogus. The comments says that we check > that we do not have SME enabled for a pKVM guest but the assert actually > checks to see if the host has anything set in SVCR which is unrelated to > the guest features or state, regardless of if those guests are protected > or not. This check is also made in the hypervisor, it will refuse to run > a guest if the check fails, so it appears that the assert here is > intended to improve diagnostics. > > Update the comment to reflect the check in the code, and to clarify that > we do actually enforce this in the hypervisor. While we're here also > update to use a WARN_ON_ONCE() to avoid log spam if this triggers. > > Fixes: afb91f5f8ad7 ("KVM: arm64: Ensure that SME controls are disabled in protected mode") > Reviewed-by: Fuad Tabba > Signed-off-by: Mark Brown > --- > This has been sent with v6.10 with only positive review comments after > the first revision, if there is some issue with the change please share > it. > > To: Marc Zyngier > To: Oliver Upton > To: James Morse > To: Suzuki K Poulose > To: Catalin Marinas > To: Will Deacon > To: Fuad Tabba > --- > Changes in v6: > - Rebase onto v6.14-rc1. > - Link to v5: https://lore.kernel.org/r/20241210-kvm-arm64-sme-assert-v5-1-995c8dd1025b@kernel.org > > Changes in v5: > - Rebase onto v6.13-rc1. > - Link to v4: https://lore.kernel.org/r/20240930-kvm-arm64-sme-assert-v4-1-3c9df71db688@kernel.org > > Changes in v4: > - Rebase onto v6.12-rc1 > - Link to v3: https://lore.kernel.org/r/20240730-kvm-arm64-sme-assert-v3-1-8699454e5cb8@kernel.org > > Changes in v3: > - Rebase onto v6.11-rc1. > - Link to v2: https://lore.kernel.org/r/20240605-kvm-arm64-sme-assert-v2-1-54391b0032f4@kernel.org > > Changes in v2: > - Commit message tweaks. > - Change the assert to WARN_ON_ONCE(). > - Link to v1: https://lore.kernel.org/r/20240604-kvm-arm64-sme-assert-v1-1-5d98348d00f8@kernel.org > --- > arch/arm64/kvm/fpsimd.c | 11 +++++++---- > 1 file changed, 7 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c > index 4d3d1a2eb157047b4b2488e9c4ffaabc6f5a0818..f3455641e9c8a65470cdeb9d7daba7d59d78748e 100644 > --- a/arch/arm64/kvm/fpsimd.c > +++ b/arch/arm64/kvm/fpsimd.c > @@ -93,11 +93,14 @@ void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu) > } > > /* > - * If normal guests gain SME support, maintain this behavior for pKVM > - * guests, which don't support SME. > + * The pKVM hypervisor does not yet understand how to save or > + * restore SME state for the host so double check that if we > + * are running with pKVM we have disabled SME. The hypervisor > + * enforces this when the guest is run, this check is for > + * clearer diagnostics. > */ > - WARN_ON(is_protected_kvm_enabled() && system_supports_sme() && > - read_sysreg_s(SYS_SVCR)); > + WARN_ON_ONCE(is_protected_kvm_enabled() && system_supports_sme() && > + read_sysreg_s(SYS_SVCR)); This implies that non-protected modes do understand how to save/restore SME state, and the wording is somewhat clunky. Given we've just queued up patches requiring that the host has saved away the FPSIMD/SVE/SME state, I reckon it'd make more sense to simplify this to: /* * Protected and non-protected KVM modes require that * SVCR.{SM,ZA} == {0,0} when entering a guest so that no * host/guest SME state needs to be saved/restored by hyp code. * * In protected mode, hyp code will verify this later. */ WARN_ON_ONCE(system_supports-sme() && read_sysreg_s(SYS_SVCR)); ... and then if/when we enable SME for non-protected modes we can constrain that further. Mark.