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 CAEB820A5DC for ; Thu, 13 Feb 2025 09:24:31 +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=1739438674; cv=none; b=U1RjrIrUe1d4t55h/ME7Rkmicq59y0nwzQ2p0Th0ihZIZQueyw1CE0kSA5/6SYplWa8gkUqn+EsoHeiyL0Si8RQWDe3V2+NMvLqJK6NNnngoQH4bvZKNCqZ8fI8gk6qDZonEI2Q94Wq2aL8930ZX+Wwvlk/n49LW30gCV1dVzyc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739438674; c=relaxed/simple; bh=iqZX9vlmTh8Gz3IOozatDHf855QCyukvJ48qmfrPENU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=e4lkXPZ3yzzpJn9GXGpw7u2bkBalrCaIIGhaU/ftuw8w8wcptpguQnnejE3uMhpuFeiGwJemwt6egxnBBnvuRPL5++Z4XH800L94juqWAJkxEbxDSc8fM77Mb0sqX3kXH/Z76T1Xe8WkQXty4Zj6vuBvUxvUAwCuhjHVKSMsTcY= 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 DE7BE16F3; Thu, 13 Feb 2025 01:24:51 -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 77FCF3F58B; Thu, 13 Feb 2025 01:24:29 -0800 (PST) Date: Thu, 13 Feb 2025 09:24:22 +0000 From: Mark Rutland To: Marc Zyngier Cc: Mark Brown , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, Fuad Tabba , Oliver Upton , James Morse , Suzuki K Poulose , Catalin Marinas , Will Deacon Subject: Re: [PATCH v7] KVM: arm64: Fix confusion in documentation for pKVM SME assert Message-ID: References: <20250212-kvm-arm64-sme-assert-v7-1-0f786db838d3@kernel.org> <86tt8yrzon.wl-maz@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: <86tt8yrzon.wl-maz@kernel.org> On Thu, Feb 13, 2025 at 08:55:52AM +0000, Marc Zyngier wrote: > On Wed, 12 Feb 2025 11:11:04 +0000, > Mark Rutland wrote: > > On Wed, Feb 12, 2025 at 12:44:57AM +0000, Mark Brown wrote: > > > diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c > > > index 4d3d1a2eb157047b4b2488e9c4ffaabc6f5a0818..e37e53883c357093ff4455f5afdaec90e662d744 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. > > > + * 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(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)); > > > > As I mentioned on the last round, we can drop the is_protected_kvm_enabled() > > check, i.e. have: > > > > /* > > * 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)); > > > > Either way: > > > > Acked-by: Mark Rutland > > > > Marc, are you happy to queue this atop the recent fixes from me? Those > > try to ensure SVCR.{SM,ZA} == {0,0} regardless of whether KVM is in > > protected mode. > > In all honesty, I find that at this stage, the comment just gets in > the way and is over-describing what is at stake here. > > The > > WARN_ON_ONCE(system_supports_sme() && read_sysreg_s(SYS_SVCR)); > > is really the only thing that matters. It perfectly shows what we are > checking for, and doesn't need an exegesis. > > As for the Fixes: tag, and given the magnitude of the actual fixes > that are already queued, I don't think we need it. That's fair; if you haven't spun a patch for that already, I guess we're after the following? Mark. ---->8---- >From 4d05f6dd6d39c747c175782b7b44daa775251994 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Thu, 13 Feb 2025 09:15:31 +0000 Subject: [PATCH] KVM: arm64: Simplify warning in kvm_arch_vcpu_load_fp() At the end of kvm_arch_vcpu_load_fp() we check that no bits are set in SVCR. We only check this for protected mode despite this mattering equally for non-protected mode, and the comment above this is confusing. Remove the comment and simplify the check, moving from WARN_ON() to WARN_ON_ONCE() to avoid spamming the log. Signed-off-by: Mark Rutland --- arch/arm64/kvm/fpsimd.c | 7 +------ 1 file changed, 1 insertion(+), 6 deletions(-) diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c index 3cbb999419af7..7f6e43d256915 100644 --- a/arch/arm64/kvm/fpsimd.c +++ b/arch/arm64/kvm/fpsimd.c @@ -65,12 +65,7 @@ void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu) fpsimd_save_and_flush_cpu_state(); *host_data_ptr(fp_owner) = FP_STATE_FREE; - /* - * If normal guests gain SME support, maintain this behavior for pKVM - * guests, which don't support SME. - */ - WARN_ON(is_protected_kvm_enabled() && system_supports_sme() && - read_sysreg_s(SYS_SVCR)); + WARN_ON_ONCE(system_supports_sme() && read_sysreg_s(SYS_SVCR)); } /* -- 2.30.2