From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1C88C13D891 for ; Tue, 17 Dec 2024 16:46:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734453966; cv=none; b=HSy3zwDZX9sh0FyyKZiL/8bkR6Q2Ul6AfIMw01N8tcBvXcQYUhZi2cDHV9wm77CFW+spReKvcJ4g2lmKpmTUhavPEIoSoznPbPwj1pIRMYH+bY/XBksN69+cD7hpUc3IPZ9U5rNdUiguPr963fAk6MdCrlWlXyq+E1xhEPBjlJk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734453966; c=relaxed/simple; bh=lRdofdyedL7gegjhv4biLCGXevi2+kvVVMA05wxKmBU=; h=From:To:Subject:Date:Message-ID:In-Reply-To:References: Content-Type:MIME-Version; b=PTOJ9IPslknnMydvFCoC4fPZo6HWebWnHi+w6HHA37lT+/CykP+XkTcNYty0CNLqMQX7FbebrXoWs+fsODwVwTDbobJFKKFRmUUY6PmqVZnVO0RBurJvV+KXgVbTNyE/BrU9IT9Lutu0sjGN36QM3DpO06mgAoXNM4lVA7Cmsy8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cKlDoSYj; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="cKlDoSYj" Received: by smtp.kernel.org (Postfix) with ESMTPS id B29FCC4CEDD for ; Tue, 17 Dec 2024 16:46:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1734453965; bh=lRdofdyedL7gegjhv4biLCGXevi2+kvVVMA05wxKmBU=; h=From:To:Subject:Date:In-Reply-To:References:From; b=cKlDoSYjl+YqMCrDvDkoict8XpY7iKrGCOt+HkDascNpexnBd5cog/uNSOOPTh6y1 EfvIR88Lc/t0lW5T2Uo8ZzxP9SK19VVCBS47duRA95cb+Fnx5+geMsl6Q3vr5rArNp +sskka2hUj03Ms0ipMN+kfN6Q2VhNU1RvExbI7siogZ04Vck5kT0b/dcZwBBiJv26E Xb84rfspsqOYBEJpPAjFZ18/OYnMnddOHvFbaChL87oJV99h1i4o8XlW98cxAEhpND qd7lFOFPiS+re4+YvFtC7I163YqJ/dh2YKdibVt4/ciEjjqR7y64qLvz/CpO/1JDYx bs6hLjD1YERgQ== Received: by aws-us-west-2-korg-bugzilla-1.web.codeaurora.org (Postfix, from userid 48) id A510DC41614; Tue, 17 Dec 2024 16:46:05 +0000 (UTC) From: bugzilla-daemon@kernel.org To: kvm@vger.kernel.org Subject: [Bug 219602] By default kvm.enable_virt_at_load breaks other virtualization solutions Date: Tue, 17 Dec 2024 16:46:05 +0000 X-Bugzilla-Reason: None X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: AssignedTo virtualization_kvm@kernel-bugs.osdl.org X-Bugzilla-Product: Virtualization X-Bugzilla-Component: kvm X-Bugzilla-Version: unspecified X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: seanjc@google.com X-Bugzilla-Status: NEW X-Bugzilla-Resolution: X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: virtualization_kvm@kernel-bugs.osdl.org X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: cc Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: https://bugzilla.kernel.org/ Auto-Submitted: auto-generated Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 https://bugzilla.kernel.org/show_bug.cgi?id=3D219602 Sean Christopherson (seanjc@google.com) changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |seanjc@google.com --- Comment #3 from Sean Christopherson (seanjc@google.com) --- >From the kernel docs: kvm.enable_virt_at_load=3D[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86] If enabled, KVM will enable virtualization in hardw= are when KVM is loaded, and disable virtualization when= KVM is unloaded (if KVM is built as a module). If disabled, KVM will dynamically enable and disable virtualization on-demand when creating and destroyi= ng VMs, i.e. on the 0=3D>1 and 1=3D>0 transitions of t= he number of VMs. Enabling virtualization at module lode avoids poten= tial latency for creation of the 0=3D>1 VM, as KVM seria= lizes virtualization enabling across all online CPUs. The "cost" of enabling virtualization when KVM is loade= d, is that doing so may interfere with using out-of-tr= ee hypervisors that want to "own" virtualization hardw= are. In addition to the latency angle, TDX support is effectively going to requi= re VMX to be enabled when KVM is loaded, i.e. trying to do something different will only delay the inevitable. FWIW, Paolo and I do want to get to a state where out-of-tree hypervisors d= on't need to do weird things, but it'll take some time to get to that state. https://lore.kernel.org/all/ZwQjUSOle6sWARsr@google.com --=20 You may reply to this email to add a comment. You are receiving this mail because: You are watching the assignee of the bug.=