From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id A424A239E66; Tue, 10 Jun 2025 16:36:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=13.77.154.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749573411; cv=none; b=tNHMFif9NZl0vzc0r25zwprUnv/T9uJW+gTndB30tIIpMDZYbzs+k3qgsUUZ7Vyuh6lL///t6RPJSiu+TP8WewQ+dqB1b9Ckpsm4OBBPV9/8RvJDBci7S15CItgUJtysGhzf5j8nRXBQRTQg1JEV5iokO72i2EB/7udHddzscNs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749573411; c=relaxed/simple; bh=2koO3b4bfhXKhsRl+EmAagbxaajqu6JzOnw0W016Kjs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=prkZ79WwGmjzc8GWRGJx9kUJ7AZARmQ8gI+aXv4h4mei75WC5C5J84PdH9naKc+/eUHghpJ9sCyTGPXrBLROjWOcVr9CAlMs32bjpST5fqeDqAfhnEVzcuFUj2lSiRRAQrbg/n/C/KENUGdHRdOaZn47q+AoWL+elaE0spB+Phg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com; spf=pass smtp.mailfrom=linux.microsoft.com; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b=igEOPax8; arc=none smtp.client-ip=13.77.154.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="igEOPax8" Received: from romank-3650.corp.microsoft.com (unknown [131.107.160.188]) by linux.microsoft.com (Postfix) with ESMTPSA id 32B392114D87; Tue, 10 Jun 2025 09:36:49 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 32B392114D87 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1749573409; bh=BKkeo+57HzITwASBg264hik1AJRnX11r4jDH2Ot6bOQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=igEOPax8Xj5Y8bZfRM8qy5YB224yUaCby1t9mu+nJp4CwRKNHtGoLIpqg0MnnhFcJ jiq8JBnM8o1qXHBX749EiyNKTn63LHN1ySp5nEChFQLgFg6WgwaMD0maqv85u3fXPz gJ7A7Y/1n1y9fDiBh6Nt7JeSepS0XO+hyJfp7UbA= From: Roman Kisel To: mhklinux@outlook.com Cc: arnd@arndb.de, arnd@kernel.org, decui@microsoft.com, haiyangz@microsoft.com, kys@microsoft.com, linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org, nunodasneves@linux.microsoft.com, romank@linux.microsoft.com, ssengar@linux.microsoft.com, wei.liu@kernel.org Subject: RE: [PATCH] hv: add CONFIG_EFI dependency Date: Tue, 10 Jun 2025 09:36:47 -0700 Message-ID: <20250610163647.17887-1-romank@linux.microsoft.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-hyperv@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit >the VTL2 paravisor is supported only in Generation 2 VMs. But I'm not clear on >what dependencies on EFI the VTL2 paravisor might have, if any. Roman -- are >VTL2 paravisors built with CONFIG_EFI=n? Thank you, Michael, for your help! We disable EFI: * https://github.com/microsoft/OHCL-Linux-Kernel/blob/product/hcl-main/6.12/Microsoft/hcl-arm64.config * https://github.com/microsoft/OHCL-Linux-Kernel/blob/product/hcl-main/6.12/Microsoft/hcl-x4.config > >> >> >> > >> > Hyper-V as of recent can boot off DeviceTree with the direct kernel boot, no UEFI >> > is required (examples would be OpenVMM and the OpenHCL paravisor on arm64). >> >> I was aware of hyperv no longer needing ACPI, but devicetree and UEFI >> are orthogonal concepts, and I had expected that even the devicetree >> based version would still get booted using a tiny UEFI implementation >> even if the kernel doesn't need that. Do you know what type of bootloader >> is actually used in the examples you mentioned? Does the hypervisor >> just start the kernel at the native entry point without a bootloader >> in this case? > >Need Roman to clarify this. > The kernel is started at the native entry point in "Image", and the address of the DeviceTree blob is passed in X0. There is a "virtual baremetal" bootloader [1] that prepares DeviceTree for the kernel, sets some CPU registers and jumps to the Image's entry point yet that's totally headless except for the optional serial output. No ACPI or UEFI is involved at all. For all intents and purposes, that's the kernel direct boot :) [1] https://github.com/microsoft/openvmm/tree/main/openhcl/openhcl_boot