From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794591116; b=rm536jdpjaIJ1I8VE0V7ClXs32Xxp5oNc/+phx44s6erVMI3PaaCWfQ6m5MjZ+FncUvJ 3iaX02sNFfAsYm5eyhDMAem6DQRalKV/mSCiRDsPPPOphZVguRwkhRyuX6TBcm6zD+/rX H5PZaZknwZEZAN49f4E03Pkm8A8Iu3urU7VV/Vq2eWi0Xd+Gmm04IGeiG0o2XJSuKOldB bAe7pe4stB/kKm+MkU0MPLGZjbFIJmyBxzURzlZGdVJQVgQO0RkDFHhNcFzTURqHknGoN t/jYs3F+1kyIiClaEV8YgC0pL90SZbdlh7/HAtCagV4Iz0OPTKi4VPiENhb1aUehPTA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794591116; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=SEfjtnBb1/zQaIQKEpxXPPSn/i5RcRl6yKqDxlmBb9Y=; b=yNl2huUrWgri28cQr01uKceR6PAhLprro2QIdLT/qSMV9CnETyWkGcaU3TrCvFSVQBrr tNeZvBZk2lzho/sfQubV6acU6OqszQUWT/K3NlLLF9VVUkV590SWkbjNnu5NbkDqaHzJu MJ9sh2u36ZHY+PpIOmyynpCW5a43wxxP7uPUnhR9wpB4MbvY1rPrqJaAvBOv+diFaKlTy REVq2VQg5rl1Aqm+Hz5Qd1VEFLXFo2qIqRKKimpuuQd9+aEFW84ah9s6lJBY/rLrZBt34 Qlm3w/0YWgX9f+uzwnSsptJvE4a8jQimeYI8QweNBIZWWR7kKszD7E+6pc5vIwGG6eQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b="EBWJh/eC"; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 03840606A8B3; Fri, 13 Nov 2026 17:31:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=EBWJh/eC Received: by smtp.kernel.org (Postfix) with ESMTPSA id A38FD1F000C5; Fri, 13 Nov 2026 17:31:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794591115; bh=SEfjtnBb1/zQaIQKEpxXPPSn/i5RcRl6yKqDxlmBb9Y=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=EBWJh/eCiYkggCTpmSLDvpxex0PfVxOnx3hRc5enWS8rddsoLrCyg4JJzaXXGQyD8 Q90NfV0OYJPGPXpgQ8dGD6Sp1MR2CDPS2LJnHBw99gIvnO4ydsdRarJbtimplM7bRC JXTp7j7iA7Kgosb0ev3/TgtkVWTaUEHtKensPnFs= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Stefan Teodorescu , Sean Christopherson , Paolo Bonzini , Sasha Levin Subject: [PATCH 6.12 266/670] KVM: x86/mmu: Conditionally resched when retrying gPTE walk on A/D update failure Date: Fri, 13 Nov 2026 10:47:10 -0500 Message-ID: <20261113153820.872825746@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261113153811.177190860@linuxfoundation.org> References: <20261113153811.177190860@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Sean Christopherson [ Upstream commit b2691b3a6cd230209736c89684dab90d939aa56b ] Conditionally reschedule when retrying a guest PTE walk because the CMPXCHG to update A/D bits failed, e.g. because a different task/vCPU modified the relevant gPTEs. On kernels without involuntary preemption of some kind, a misbehaving guest can "capture" a pCPU effectively indefinitely and trigger soft lockups by continuously modifying its gPTEs such that the result of the walk is remains valid. Fixes: b3e4e63fd9ee ("KVM: MMU: Use cmpxchg for pte updates on walk_addr()") Cc: stable@vger.kernel.org Reported-by: Stefan Teodorescu Signed-off-by: Sean Christopherson Message-ID: <20261022015903.282261-1-seanjc@google.com> Signed-off-by: Paolo Bonzini Signed-off-by: Sasha Levin --- arch/x86/kvm/mmu/paging_tmpl.h | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h index 10e9e87f14203..aa6abaa601173 100644 --- a/arch/x86/kvm/mmu/paging_tmpl.h +++ b/arch/x86/kvm/mmu/paging_tmpl.h @@ -321,6 +321,13 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker, gpa_t real_gpa; gfn_t gfn; + /* + * KVM might sleep/resched when retrying the walk if the updating A/D + * fails because the gPTE changed between reading the gPTE and trying + * the CMPXHG to set A/D bits. + */ + might_sleep(); + trace_kvm_mmu_pagetable_walk(addr, access); retry_walk: walker->level = mmu->cpu_role.base.level; @@ -471,8 +478,10 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker, addr, write_fault); if (unlikely(ret < 0)) goto error; - else if (ret) + else if (ret) { + cond_resched(); goto retry_walk; + } } return 1; -- 2.53.0