From nobody Thu Oct 2 07:46:29 2025 Received: from mail-pl1-f202.google.com (mail-pl1-f202.google.com [209.85.214.202]) (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 987082FB09F for ; Fri, 19 Sep 2025 22:33:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.202 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758321233; cv=none; b=d3dceOxWLSnLgHyNghG2QiueSTaNqIcDj3pZ/gmp9D4rLqjaRRdTjTqAkrllVL5x3r6IoMrad8ACeh0N/yqJVKpttWPOHQpaNEYXjF7+5If5IMApsduHr92hl8/zcc8WwjdQObc5I3vh55uVlJXT7IpG5+7FI6kSMXqQJWNpg6I= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758321233; c=relaxed/simple; bh=/tqPBTeDuMrFe1AL4FE5D/cKrgiWfqZL6tyxrCfO6SU=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=m9fnw8b55Ba7CMtE5OATsKq4FdWX8FvRu8ZBBH324gQ+0VRmnG1Qt3Qrg+y5ZyFt7Afa3DNNmehY1qF4C4iGnvMs5wx/wwJLfJ5M9HIi0NllSJgkJzvN509fkN2j6v0jhLESYTqwEdFo7nGINX1+BJtKYr5+Voyx9QNVB2QC4lg= 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=fOK0S79l; arc=none smtp.client-ip=209.85.214.202 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="fOK0S79l" Received: by mail-pl1-f202.google.com with SMTP id d9443c01a7336-24456ebed7bso32555345ad.0 for ; Fri, 19 Sep 2025 15:33:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1758321231; x=1758926031; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:from:to:cc:subject:date:message-id:reply-to; bh=HedB0vqjCe4vRRpTggbdQsycmWfrhYSfaZmK+vmSq88=; b=fOK0S79l7H4WA0EbcTcovTJcXBa49hpS1Wv3uL0TCmgk9opC+S0z8AEMnaCnhFRppp onmPslFCJ0MLZDZ9Whpoxw8/gZ3iHL4hFEhYFKW/9pIGj/ruq10gNIYXrk24Vr+u32z0 MRVuMlX/IKx80+nhdLmd/v5gces8fbRgZJinAXVpzzRzGtsQmYRJcklirdgh8wDH4eWn ViWdW+hx0OqzqGw9nmWtK6pQn4//unZNqsl02pLgB/aT4PUguupPQosgBhuAbaSUqEL1 NdvkPTz3im3ProQD4aNTnokbiLzL53+k3Yo/zr7mTuYe5ti1tYUh8fKTM2f4nnqJ+C3u MqYA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1758321231; x=1758926031; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=HedB0vqjCe4vRRpTggbdQsycmWfrhYSfaZmK+vmSq88=; b=NbicgFNqkYHABp1xcHa0IXNnJKCw874j+y+XW1sW9OIidG5UPTHiuUJPNmcF1mE94a jw+T7wbDD7c21+GIvpg/c5b/QjAN4c5l06YFM1DIYYz/fZuVQCKTUDZEa6Rz/hr3rYGn ruTMxGt/5OM4WC8rhstG35t16E2mopzJPJNWqpWTwUDEhdbcmIiLgZDPgtRBBGZlJUN4 e8poLF5CHNrOX6ztFEwDWDPfT7ro1VUeIenKnLP7+srBl+icC4A8Fl1ZjtTZwgQXDQsh 2we6tpuqGBRBg4fhywe1tjxoroR83WQzCnC+WNAJTdX+ddAD9FjMithtYPVU9M6HI4lT GHiA== X-Forwarded-Encrypted: i=1; AJvYcCXS6Ln62j5mLgUYtHPH5S1jY+kk8n7RYGgs6iQZwa+xcSPkxcVfLNI/BJ5rRRo3b5ArJaqo932//0myhrE=@vger.kernel.org X-Gm-Message-State: AOJu0YyTo8g461PCeU7zbPCCurzqNBNa4PBF9v63hxpsTEoaLLqAxVCs Xgkw92ejNPSmiC6fdc622856wKRlYh9qhXqFcPvr1fS35w0VvxvRowk+xBxSapzrnsdtzoRsrPc m28U8jA== X-Google-Smtp-Source: AGHT+IEljnIzRoy1UyE5BtCbUU4Z9ZtjJtcURZf7n7UmCN9hEURvx8fd1jTPH7oZwx5u199EJlJyB4GvKnY= X-Received: from pjbsw8.prod.google.com ([2002:a17:90b:2c88:b0:32e:e155:ee48]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:cec8:b0:267:99be:628e with SMTP id d9443c01a7336-2697c7ea3c2mr109901915ad.2.1758321231052; Fri, 19 Sep 2025 15:33:51 -0700 (PDT) Reply-To: Sean Christopherson Date: Fri, 19 Sep 2025 15:32:33 -0700 In-Reply-To: <20250919223258.1604852-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250919223258.1604852-1-seanjc@google.com> X-Mailer: git-send-email 2.51.0.470.ga7dc726c21-goog Message-ID: <20250919223258.1604852-27-seanjc@google.com> Subject: [PATCH v16 26/51] KVM: x86: Disable support for Shadow Stacks if TDP is disabled From: Sean Christopherson To: Paolo Bonzini , Sean Christopherson Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Tom Lendacky , Mathias Krause , John Allen , Rick Edgecombe , Chao Gao , Binbin Wu , Xiaoyao Li , Maxim Levitsky , Zhang Yi Z , Xin Li Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Make TDP a hard requirement for Shadow Stacks, as there are no plans to add Shadow Stack support to the Shadow MMU. E.g. KVM hasn't been taught to understand the magic Writable=3D0,Dirty=3D0 combination that is required for Shadow Stack accesses, and so enabling Shadow Stacks when using shadow paging will put the guest into an infinite #PF loop (KVM thinks the shadow page tables have a valid mapping, hardware says otherwise). Signed-off-by: Sean Christopherson Reviewed-by: Binbin Wu Reviewed-by: Xiaoyao Li --- arch/x86/kvm/cpuid.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 32fde9e80c28..499c86bd457e 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -955,6 +955,14 @@ void kvm_set_cpu_caps(void) if (!tdp_enabled || !boot_cpu_has(X86_FEATURE_OSPKE)) kvm_cpu_cap_clear(X86_FEATURE_PKU); =20 + /* + * Shadow Stacks aren't implemented in the Shadow MMU. Shadow Stack + * accesses require "magic" Writable=3D0,Dirty=3D1 protection, which KVM + * doesn't know how to emulate or map. + */ + if (!tdp_enabled) + kvm_cpu_cap_clear(X86_FEATURE_SHSTK); + kvm_cpu_cap_init(CPUID_7_EDX, F(AVX512_4VNNIW), F(AVX512_4FMAPS), --=20 2.51.0.470.ga7dc726c21-goog