From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f197.google.com (mail-pf1-f197.google.com [209.85.210.197]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 541CB3C1A for ; Tue, 28 Jul 2026 00:23:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.197 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785198210; cv=none; b=ZOiQoVIi8QjfO+qmoCbUcph/tnlqjExCwgg//r3FU/Yrz+GIxkaPJjlQ4DovCF5cdEz7KxR0/FjRsiAS3vMfnASeiaqJ7K/i6iKRmj1/mFblP399Hsz1WL72iJTVvbcaY7IQOdz+BHP6DeIw7VOBQExd+F1v5wTJhTjLvamxbO8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785198210; c=relaxed/simple; bh=3PhHS4cx87d1kDraniHXJ5Yt8qZeJOak/oW7RUNtkb0=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=WP05oLzkLH9aRFoIXo2SZMBWP9Bkaxorx95hPZ5OVN1e3a+eiSzngRksexJ17bCkcEwVlaODlo0y6P8asVATtzW0Opwrp6UhBbnwwv2HvMYawtmefotGrzBZV9JvU9X79dJC2w++Fk9PVm9CqNZ05DTiH3mj/QvpwOY4UegEcIU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=pgWtQ1de; arc=none smtp.client-ip=209.85.210.197 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="pgWtQ1de" Received: by mail-pf1-f197.google.com with SMTP id d2e1a72fcca58-8487eb67173so5301267b3a.2 for ; Mon, 27 Jul 2026 17:23:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1785198209; x=1785803009; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:mime-version:date :reply-to:from:to:cc:subject:date:message-id:reply-to:content-type; bh=xFS92TdOEy1I4tDpJqHj1DWKbqALk3IhZSaExM65JNM=; b=pgWtQ1denGEQxxQPLtnu5Fcw7wXH3bvGg/RxWAW98VeWzCifAYs/ULRXoXUhqABXxj 8X7mwePDDgL3XXr9Q8aAe7HKgBdVlQ/7gNwrFJ7gGVMyrGs9omAxUTwXaEqpbDK1lhhY JQ2j8e4tXrLNf8n9Kt2/hU7z+1Q6O/oosrjOMmvdfWbHfrAlO+8gUBECTrpVnY/1ZBRM Mux20IEDmcnJKE5hrHYg2SsBOjdVtxW9yXr9SNSUEDTplpH7cj8Z+SXfRhtILvZsSX4p ZY1oLncLkV7y1w3rpaEsY93iq3HGB17D3qJH6RzwvSe5CxkB29FlABSyhqqYuvgyIPkA v6/g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1785198209; x=1785803009; h=content-type:cc:to:from:subject:message-id:mime-version:date :reply-to:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to:content-type; bh=xFS92TdOEy1I4tDpJqHj1DWKbqALk3IhZSaExM65JNM=; b=ZFMzCwEu532HWBerxOEl7NEdPzer9ZrKXwNcYPYFulYa6ss+yTtmsEqqZLONrjCu2V izd9ap3Uu9cCI9DZ6rImK4ISUpP8wsJwzo2CFmE1POIpqnsRNrMXcysT0CcxKSmy5Rub UwftQFEcHumKto6T1+x+ggVVqplSkm5ihNY6soj+TcNBmioSJCUKHUpyXzuBqWGceAVF KNo1zVKmZE+GO34h8IGT38Xfpn/BldujnAhkKL8TQ2fTr+bmwUDUlfzzuuxPa0NxMkhA 5bCnGypd7QuXbeLkB/25mYDtLD5SUYu0D/N/vHEpp+2hgMhYolFIdxXcj0ahT89whAu+ 57Bw== X-Forwarded-Encrypted: i=1; AHgh+RqDCq+iZ7lUZXUV5zJfdndFKwt1bvM1MPl3Ak/wD2QDuqJMpWFFyqxpb73/3Ahdtt409Agy0+7qgXXaaz8=@vger.kernel.org X-Gm-Message-State: AOJu0Yy9wIZe+FE8RM2QzWYt/ml2J/iOhwalIXAuOhPuD5MvsafKcBUP L8UdnPdGoKECfNh9TC5Bdb7jhmGIrg3QsaX58TSZA3sZLpXQkuKZmXYhaRMH/T9git/KGnFxCIQ ZQ6+08A== X-Received: from pgee11.prod.google.com ([2002:a63:1e0b:0:b0:c9b:2759:d240]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:2e91:b0:848:7b92:8e68 with SMTP id d2e1a72fcca58-84e933613b2mr96021b3a.66.1785198208421; Mon, 27 Jul 2026 17:23:28 -0700 (PDT) Reply-To: Sean Christopherson Date: Mon, 27 Jul 2026 17:22:34 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.55.0.229.g6434b31f56-goog Message-ID: <20260728002236.869865-1-seanjc@google.com> Subject: [PATCH 0/2] KVM: x86/mmu: Use LOCK CMPXCHG to clear Accessed bits From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, James Houghton Content-Type: text/plain; charset="UTF-8" Use LOCK CMPXCHG instead of LOCK AND or LOCK BTR to clear Accessed bits when aging SPTEs, as LOCK AND could clobber a !PRESENT SPTE. Specificaly, as flagged by AI of some kind, a LOCK AND in the TDP MMU could clobber a FROZEN_SPTE and ultimately result in a false negative since the Accessed bit is included in FROZEN_SPTE. I initially was planning on tweaking the FROZEN_SPTE value to make it ok to use LOCK AND on Accessed bits, but AFAICT there's no meaningful downside to using CMPXCHG. Sean Christopherson (2): KVM: x86/mmu: Use CMPXCHG when clearing Accessed bit in TDP MMU KVM: x86/mmu: Use CMPXCHG when clearing Accessed bit in the shadow MMU arch/x86/kvm/mmu/mmu.c | 27 ++++++++++++++------------- arch/x86/kvm/mmu/tdp_iter.h | 7 +++++++ arch/x86/kvm/mmu/tdp_mmu.c | 20 +++++++++----------- 3 files changed, 30 insertions(+), 24 deletions(-) base-commit: 271255273d5ff348fe29d89fe4712b2f7f7907c3 -- 2.55.0.229.g6434b31f56-goog