From nobody Wed Dec 17 10:45:01 2025 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 50E91262FD9; Sun, 11 May 2025 23:08:07 +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=1747004888; cv=none; b=HFl9KbQQfcfrskRsCTCZLZmB2szVGTmOI/3SNzYvmUzgjwbTYNAJm4y78U76hhX2otXfzlza/S99lfCfiCqLVeBpeZMctyuKuUy7VXsA62sqAYsjboJGS13MIcxd+oaqn18N1XfrGoNnhf1efMtfonQ+lOaueADoNLpXoyOZa0w= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747004888; c=relaxed/simple; bh=TFgAoICDPd7+D0MXWe9Ure6mza2fxuJqgIO6/JilKiU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=npRliZbMw/76HBoTdGk9EUAp04lZsNpNdE8SQ4jTEboy0nwJOxxZtlOBTTNJ/RisxY9nw32yg6D4QkV2fdVRE+hvu0oMoTOd29Xskf/axjNg6v/uaBaPTosnyHjX8pxEpeSj0S4KonCpJcz+echsO2GdbZ/eeRNoQkEJbiV61EQ= 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=i/uIweLM; 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="i/uIweLM" Received: from romank-3650.corp.microsoft.com (unknown [131.107.1.188]) by linux.microsoft.com (Postfix) with ESMTPSA id B2B49211D8B6; Sun, 11 May 2025 16:08:00 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com B2B49211D8B6 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1747004880; bh=C6e1Sd2wwIBHFKi64bmr0cXUFCAbG2BTPif+GBdvk8k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=i/uIweLM/AnCi7PqtxtdfyJTudA/+61xNiWRDAoghEYqfW7si/lWX7uVlaaVMDyX4 9jA91EjAJ3yihJuaC9vdYgkFDLfWxORvxvnRIEuSYhal1jDUg7Xu1XR3GOg9Em6cLH npeCsKoJGHstFIFm1zrocmvdPk38BL1CW+0I/kEY= From: Roman Kisel To: arnd@arndb.de, bp@alien8.de, catalin.marinas@arm.com, corbet@lwn.net, dave.hansen@linux.intel.com, decui@microsoft.com, haiyangz@microsoft.com, hpa@zytor.com, kys@microsoft.com, mingo@redhat.com, tglx@linutronix.de, wei.liu@kernel.org, will@kernel.org, x86@kernel.org, linux-hyperv@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org Cc: apais@microsoft.com, benhill@microsoft.com, bperkins@microsoft.com, sunilmut@microsoft.com Subject: [PATCH hyperv-next v2 1/4] Documentation: hyperv: Confidential VMBus Date: Sun, 11 May 2025 16:07:55 -0700 Message-ID: <20250511230758.160674-2-romank@linux.microsoft.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20250511230758.160674-1-romank@linux.microsoft.com> References: <20250511230758.160674-1-romank@linux.microsoft.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Define what the confidential VMBus is and describe what advantages it offers on the capable hardware. Signed-off-by: Roman Kisel --- Documentation/virt/hyperv/vmbus.rst | 41 +++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+) diff --git a/Documentation/virt/hyperv/vmbus.rst b/Documentation/virt/hyper= v/vmbus.rst index 1dcef6a7fda3..ca2b948e5070 100644 --- a/Documentation/virt/hyperv/vmbus.rst +++ b/Documentation/virt/hyperv/vmbus.rst @@ -324,3 +324,44 @@ rescinded, neither Hyper-V nor Linux retains any state= about its previous existence. Such a device might be re-added later, in which case it is treated as an entirely new device. See vmbus_onoffer_rescind(). + +Confidential VMBus +------------------ + +The confidential VMBus provides the control and data planes where +the guest doesn't talk to either the hypervisor or the host. Instead, +it relies on the trusted paravisor. The hardware (SNP or TDX) encrypts +the guest memory and the register state also measuring the paravisor +image via using the platform security processor to ensure trusted and +confidential computing. + +To support confidential communication with the paravisor, a VMBus client +will first attempt to use regular, non-isolated mechanisms for communicati= on. +To do this, it must: + +* Configure the paravisor SIMP with an encrypted page. The paravisor SIMP = is + configured by setting the relevant MSR directly, without using GHCB or t= dcall. + +* Enable SINT 2 on both the paravisor and hypervisor, without setting the = proxy + flag on the paravisor SINT. Enable interrupts on the paravisor SynIC. + +* Configure both the paravisor and hypervisor event flags page. + Both pages will need to be scanned when VMBus receives a channel interru= pt. + +* Send messages to the paravisor by calling HvPostMessage directly, withou= t using + GHCB or tdcall. + +* Set the EOM MSR directly in the paravisor, without using GHCB or tdcall. + +If sending the InitiateContact message using non-isolated HvPostMessage fa= ils, +the client must fall back to using the hypervisor synic, by using the GHCB= /tdcall +as appropriate. + +To fall back, the client will have to reconfigure the following: + +* Configure the hypervisor SIMP with a host-visible page. + Since the hypervisor SIMP is not used when in confidential mode, + this can be done up front, or only when needed, whichever makes sense for + the particular implementation. + +* Set the proxy flag on SINT 2 for the paravisor. --=20 2.43.0