From nobody Wed Apr 8 04:44:47 2026 Received: from mail-pl1-f201.google.com (mail-pl1-f201.google.com [209.85.214.201]) (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 5BF123C9431 for ; Tue, 10 Mar 2026 23:48:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773186524; cv=none; b=J1v6JF87C6z2j+cccibV4T9W2m3LB/bGzcHj+v4PLROFn3EYs75nhqNw/Jjo6FerzZj3/p+IMUv/enrhubhtBlY1ODe0w1o95xpRsFwPCqsCgzoRGp089MMXSLE+ODDS9NpQLvpH46vzO0LY94m2WIFKqQLEZVmW3KygLJ72cxs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773186524; c=relaxed/simple; bh=wCT56whpBWZMgqHPWbSdWWOQ4rqPp8/QKwF0p6KcqTM=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=Yo4Izy0FrmRaMy2833BOKsdWhkOe6wYaZnFtgMU13/t7LHu4Rmggiw2ZbHlHiW/iyvhk2N6oJ3MxaaAuNTiZ/zjBIORZze9eApcKeVaRoVZihGjiFPHfSrdG8AWsxpkY1hZ5O13inZUO7Y3XkYkMlxdi3+GvKp251put5ixwrv8= 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=MTG40A8o; arc=none smtp.client-ip=209.85.214.201 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="MTG40A8o" Received: by mail-pl1-f201.google.com with SMTP id d9443c01a7336-2ae6961bff0so398920895ad.2 for ; Tue, 10 Mar 2026 16:48:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1773186523; x=1773791323; 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=W84stS8+3WuLFZ+raEjrLuySDqRuwilAh+kUtsTzbCI=; b=MTG40A8o8HFRc56mbZoD+RnrWksX9sLnJSborcfiBrgXuZQ04LD3p4aEAd+o83xzRL IAhnpqxz3qn7Vu5HcS7cnV2BzvgGUX/QTTaPW4ftnEbNdx/Qz5c3Pxxt4bdZLWEdkHa5 OrCn95ETrY28pRhjsUBDt2q9EaVFjG+DE3EdTaa1bQcwWu/RVQRLYek6UkYHkKc2aiUJ FXjWWKR/1HbukBfhMvIRTCR1kqTViA1+ZVNwwJuGCiXjSwNBaWTkwu6GG1JUMXWQofdB lb4eJcO2ei/ITzSBXts9eW0zRnPlJWVDJ+S357Ab83LXPkCI/cbRm6VGnOu8t74IPi7z zRkA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1773186523; x=1773791323; 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=W84stS8+3WuLFZ+raEjrLuySDqRuwilAh+kUtsTzbCI=; b=mpf/Z1wS79Lm8j7SfmFC383DDUOEltUpay/YKDC1wCZC3LivRhv6pG80nVmFOEb4SL STW2gg6AoSFU46HjgVQmLSKAW0okMj+lGGhHw5keei8CmQFEcIm6NvPE6w98zDLm4TdQ i/JKsxpMz+W/lXezPdMPSaeYhxWmSbS5t9dRxk0Ia1AOETig0Pz98OZwYkGIb5/dyjr7 T3pKiCoJ4/D0auWpKDDriBvinZFnF8zxOlpswqZXOJZHf5gZAD+gghgLQeZEH3v454Yf xpD1NpBxrzL9qa/J2/ApyWRaQnGF3xgW7Z0kDm1TuJ3zLnoPJOs48R7D3TbuIBOyFFGf n+5Q== X-Forwarded-Encrypted: i=1; AJvYcCVXZ3uqsLnLUbPKoEJGB6uZMJAftLDfrwjORE5BmB0u5WdV4rrDegrz/ywoleKPG+lz0SxfyC8DRpeylOE=@vger.kernel.org X-Gm-Message-State: AOJu0Yzp7lVe1ARceD9jvI2qH4fP0uBiGvUMgvzfhJ6H3DnBjZQk4mvu 5F6EeaviPLwlD/PleZ7C6PjCOJurZ9/ZraxAzFA76o2UjhF11QsfTNR1d+dmOwIAQzaYt8eaYi0 SFiEJDw== X-Received: from pgbcz14.prod.google.com ([2002:a05:6a02:230e:b0:c73:7981:791d]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:903:2f92:b0:2ae:5723:afb2 with SMTP id d9443c01a7336-2aeae90050bmr4364395ad.54.1773186522529; Tue, 10 Mar 2026 16:48:42 -0700 (PDT) Reply-To: Sean Christopherson Date: Tue, 10 Mar 2026 16:48:12 -0700 In-Reply-To: <20260310234829.2608037-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260310234829.2608037-1-seanjc@google.com> X-Mailer: git-send-email 2.53.0.473.g4a7958ca14-goog Message-ID: <20260310234829.2608037-5-seanjc@google.com> Subject: [PATCH 04/21] KVM: SEV: Disallow LAUNCH_FINISH if vCPUs are actively being created From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Jethro Beekman , Alexander Potapenko , "=?UTF-8?q?Carlos=20L=C3=B3pez?=" Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Reject LAUNCH_FINISH for SEV-ES and SNP VMs if KVM is actively creating one or more vCPUs, as KVM needs to process and encrypt each vCPU's VMSA. Letting userspace create vCPUs while LAUNCH_FINISH is in-progress is "fine", at least in the current code base, as kvm_for_each_vcpu() operates on online_vcpus, LAUNCH_FINISH (all SEV+ sub-ioctls) holds kvm->mutex, and fully onlining a vCPU in kvm_vm_ioctl_create_vcpu() is done under kvm->mutex. I.e. there's no difference between an in-progress vCPU and a vCPU that is created entirely after LAUNCH_FINISH. However, given that concurrent LAUNCH_FINISH and vCPU creation can't possibly work (for any reasonable definition of "work"), since userspace can't guarantee whether a particular vCPU will be encrypted or not, disallow the combination as a hardening measure, to reduce the probability of introducing bugs in the future, and to avoid having to reason about the safety of future changes related to LAUNCH_FINISH. Cc: Jethro Beekman Closes: https://lore.kernel.org/all/b31f7c6e-2807-4662-bcdd-eea2c1e132fa@fo= rtanix.com Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson --- arch/x86/kvm/svm/sev.c | 10 ++++++++-- include/linux/kvm_host.h | 7 +++++++ 2 files changed, 15 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index 7da040baba1c..5de36bbc4c53 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -1030,6 +1030,9 @@ static int sev_launch_update_vmsa(struct kvm *kvm, st= ruct kvm_sev_cmd *argp) if (!sev_es_guest(kvm)) return -ENOTTY; =20 + if (kvm_is_vcpu_creation_in_progress(kvm)) + return -EBUSY; + kvm_for_each_vcpu(i, vcpu, kvm) { ret =3D mutex_lock_killable(&vcpu->mutex); if (ret) @@ -2050,8 +2053,8 @@ static int sev_check_source_vcpus(struct kvm *dst, st= ruct kvm *src) struct kvm_vcpu *src_vcpu; unsigned long i; =20 - if (src->created_vcpus !=3D atomic_read(&src->online_vcpus) || - dst->created_vcpus !=3D atomic_read(&dst->online_vcpus)) + if (kvm_is_vcpu_creation_in_progress(src) || + kvm_is_vcpu_creation_in_progress(dst)) return -EBUSY; =20 if (!sev_es_guest(src)) @@ -2450,6 +2453,9 @@ static int snp_launch_update_vmsa(struct kvm *kvm, st= ruct kvm_sev_cmd *argp) unsigned long i; int ret; =20 + if (kvm_is_vcpu_creation_in_progress(kvm)) + return -EBUSY; + data.gctx_paddr =3D __psp_pa(sev->snp_context); data.page_type =3D SNP_PAGE_TYPE_VMSA; =20 diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 34759a262b28..3c7f8557f7af 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -1029,6 +1029,13 @@ static inline struct kvm_vcpu *kvm_get_vcpu_by_id(st= ruct kvm *kvm, int id) return NULL; } =20 +static inline bool kvm_is_vcpu_creation_in_progress(struct kvm *kvm) +{ + lockdep_assert_held(&kvm->lock); + + return kvm->created_vcpus !=3D atomic_read(&kvm->online_vcpus); +} + void kvm_destroy_vcpus(struct kvm *kvm); =20 int kvm_trylock_all_vcpus(struct kvm *kvm); --=20 2.53.0.473.g4a7958ca14-goog