From nobody Tue Dec 16 14:38:14 2025 Received: from mail-pj1-f73.google.com (mail-pj1-f73.google.com [209.85.216.73]) (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 7EBEE384B93 for ; Thu, 30 Oct 2025 20:10:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.73 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761855037; cv=none; b=s3YKsxYNEnuGDnCTPtqVEZei8xIdqIFkFL/9EeVK8mUZAwqQa3meEjA7p8v4ydY0Ng09/wncqQKCk7qaAhohXQ2T5swTOs72azo60UWzuDezNJzQqDyPCfw7hOhldOJrHwHZZaXuG/XywW2SN2HgZQmm4OR8JCXiGdOTn0azLWo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761855037; c=relaxed/simple; bh=hZ6oGgJsAxLyizwY2nBkXOfX86m8d4LnroP9LBDe0vw=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=c3LURGjGa30J9iTx2FAO6jIHACbuAoOByxlDaEl7lTZf4cTsB0fNcz8jZt2+FwTGb6V1rf26PnGxNzDIDaaecUbntIcKwLipls65tG9j5O+hv48b6uxfhttLwxaxZBQ00sraUNgvBgXOR9oLzdEX2hT5ZZ5s7/CQNCZ9UL8YiN0= 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=3A5p7Oup; arc=none smtp.client-ip=209.85.216.73 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="3A5p7Oup" Received: by mail-pj1-f73.google.com with SMTP id 98e67ed59e1d1-3403e994649so3115347a91.3 for ; Thu, 30 Oct 2025 13:10:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1761855035; x=1762459835; 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=2Qp65v2XVpj2mbgYoCIcn74lwhNS3G3VX8VrR6k2zs8=; b=3A5p7OupYLEJL57URKNOGGxMM98HcF2+WLquTZNZSBnthoI4ayXJ79BYxCdhf7/4pF swxficeXIf1dR4LyNeI44RUUdALRJwXVxauonNboTc+f3cHbKPfZXrwmBQHViRCWUqxt 9Hc+LNbVZ7Z0dTGdT9OpFid8zN1bZbkcjOI5T6cSDNiJdpOIaD1mhWvNIHnNVw12eTvi CVehsXqeBU9U9Y37MlV51XRHI1vTzsPtxPcgLSLlZPZFy/YIVW1wXsRVbzk3UTcrf+Av qlulcr9TfTcOA5W1cMLWMo76X5sTSFD1l7OLbJaPu6OLhYweZU/lnb+iT9cy7KHKjzy5 39xw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1761855035; x=1762459835; 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=2Qp65v2XVpj2mbgYoCIcn74lwhNS3G3VX8VrR6k2zs8=; b=flZIG0ZrisO43Cu9NIvcAqaXDmmDsBEb+BRJjBFZcBlnKQs8hIeXau991btvaNpk13 oMAjz5FdOOxaDcME+UoG+Te5pQMkTKE5IXahEdj2pwC+tNiiAc52L9hkC6c9fGddo3a5 3unO/eOz1fNkv4iAjWtB3lARyd+o6MCln5DaJ2jm5CatDMGzpcih5+iAn/CI/MHbzaVX b4gKXOF9QRV/f/7AR2b2RcvPS+NCVhBIqnfVeHpptcS7mj005+u11tstDbBfl7BeE5Ck muGU9jXJikFcyg30M4urKbZxPFZEWdJcWSEyL3vjKUbtY7Roc61JZ5YLZFXe2CBmO292 4TCQ== X-Forwarded-Encrypted: i=1; AJvYcCXjybGj4hhyQXc3bvXKgLk5YK8Cv1mRNzk9NfIY0chA0i8p5UNr1z9/FwDabD/GKiZ0PB7pIrno2tnAWps=@vger.kernel.org X-Gm-Message-State: AOJu0Yy5XylYT2XTbYE++f7DNrrlXcmAQrLKYjDvRnF6JY89Gz686Frz 5+Q2kyq/Y3oPK87zVOazAwZUSunVGMYm/+vuDjbQZY53DkdEmlsRbRRr1cm9wQDqMUxIxbzzyJM 4OdguAQ== X-Google-Smtp-Source: AGHT+IHtEBN2FzRvx/PBMIz+g6mN5JL6fejVbo3/Jj6z8BZ8mwuwi1S8UZTxug0dqnAA2vI1WFCMGP+gtTc= X-Received: from pjph23.prod.google.com ([2002:a17:90a:9c17:b0:340:2aef:8b01]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:3842:b0:335:2eef:4ca8 with SMTP id 98e67ed59e1d1-34083088cfamr1279023a91.33.1761855034597; Thu, 30 Oct 2025 13:10:34 -0700 (PDT) Reply-To: Sean Christopherson Date: Thu, 30 Oct 2025 13:09:37 -0700 In-Reply-To: <20251030200951.3402865-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20251030200951.3402865-1-seanjc@google.com> X-Mailer: git-send-email 2.51.1.930.gacf6e81ea2-goog Message-ID: <20251030200951.3402865-15-seanjc@google.com> Subject: [PATCH v4 14/28] KVM: TDX: Use atomic64_dec_return() instead of a poor equivalent From: Sean Christopherson To: Marc Zyngier , Oliver Upton , Tianrui Zhao , Bibo Mao , Huacai Chen , Madhavan Srinivasan , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Sean Christopherson , Paolo Bonzini , "Kirill A. Shutemov" Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, x86@kernel.org, linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org, Ira Weiny , Kai Huang , Binbin Wu , Michael Roth , Yan Zhao , Vishal Annapurve , Rick Edgecombe , Ackerley Tng Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Use atomic64_dec_return() when decrementing the number of "pre-mapped" S-EPT pages to ensure that the count can't go negative without KVM noticing. In theory, checking for '0' and then decrementing in a separate operation could miss a 0=3D>-1 transition. In practice, such a condition is impossible because nr_premapped is protected by slots_lock, i.e. doesn't actually need to be an atomic (that wart will be addressed shortly). Don't bother trying to keep the count non-negative, as the KVM_BUG_ON() ensures the VM is dead, i.e. there's no point in trying to limp along. Reviewed-by: Rick Edgecombe Reviewed-by: Ira Weiny Reviewed-by: Binbin Wu Signed-off-by: Sean Christopherson --- arch/x86/kvm/vmx/tdx.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c index db64a9e8c6a5..99db19e02cf1 100644 --- a/arch/x86/kvm/vmx/tdx.c +++ b/arch/x86/kvm/vmx/tdx.c @@ -1726,10 +1726,9 @@ static int tdx_sept_zap_private_spte(struct kvm *kvm= , gfn_t gfn, tdx_no_vcpus_enter_stop(kvm); } if (tdx_is_sept_zap_err_due_to_premap(kvm_tdx, err, entry, level)) { - if (KVM_BUG_ON(!atomic64_read(&kvm_tdx->nr_premapped), kvm)) + if (KVM_BUG_ON(atomic64_dec_return(&kvm_tdx->nr_premapped) < 0, kvm)) return -EIO; =20 - atomic64_dec(&kvm_tdx->nr_premapped); return 0; } =20 @@ -3161,8 +3160,7 @@ static int tdx_gmem_post_populate(struct kvm *kvm, gf= n_t gfn, kvm_pfn_t pfn, goto out; } =20 - if (!KVM_BUG_ON(!atomic64_read(&kvm_tdx->nr_premapped), kvm)) - atomic64_dec(&kvm_tdx->nr_premapped); + KVM_BUG_ON(atomic64_dec_return(&kvm_tdx->nr_premapped) < 0, kvm); =20 if (arg->flags & KVM_TDX_MEASURE_MEMORY_REGION) { for (i =3D 0; i < PAGE_SIZE; i +=3D TDX_EXTENDMR_CHUNKSIZE) { --=20 2.51.1.930.gacf6e81ea2-goog