From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 4506D1422D8 for ; Thu, 25 Jul 2024 05:54:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721886871; cv=none; b=WSCSBm80v+hdS5Rdl5IRjeIKRtqipq+rPa5ABb1e3fqiUWvYjS5Qk+WU+ASPS8qVFsxHpa3kYaKCpgUKfohWQ9b5G6Eg4fnLqkt6Hw/QPrMloJvLbkcWPQoLMB5hFVsiK5SXiguQ5Os1z4U5a3VLU6YivNKVbjcMJDo5s45Dbyw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721886871; c=relaxed/simple; bh=gAZvwL67v0vt6xsxrH6XS/itsYUgy+inKlxURoSIcdU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=OH3GluwRKq+Dfg3VVXE1U3e3lGUvYqK5c/GVTWr72uQ5O98SFMVt/8GNe3hUwoqojP5Adg98DQuybn8j4U+Hw0t6+g+RBNLzh3sZ/1Jl0wcO11MFCj9SOuv1M9VMTFm61odQFXfupJQFcnpF+OzSaSzA4S8HNvwKtO98ZwgHTzY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=RJ85KjAf; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="RJ85KjAf" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1721886867; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Dh3yyuBj9HXf2A5cEfYqf0NaFgetwfgWSnefr6wKli8=; b=RJ85KjAf4UFYaMoB7MfLRAe6rPY9kt8pF1qR5U2gIeIp/fZ0Ipe5OiwnQCuk7lAu/KeWIA ykfkZyj0bozUeTA0l1e5+di5A0gEnbbGyZlhe6njP+VILyRigXN8RwO+2J0MUfHlr3tbLg Qa5/THE0xENbwWa0lnH8R0i3QIADes0= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-422-UW02cR7lPbWJfq63E80L8w-1; Thu, 25 Jul 2024 01:54:25 -0400 X-MC-Unique: UW02cR7lPbWJfq63E80L8w-1 Received: by mail-wr1-f69.google.com with SMTP id ffacd0b85a97d-36835f6ebdcso420290f8f.1 for ; Wed, 24 Jul 2024 22:54:23 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1721886860; x=1722491660; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=Dh3yyuBj9HXf2A5cEfYqf0NaFgetwfgWSnefr6wKli8=; b=Un736tGqt/cNTzwh0pMcR/plCoDMr8scXkMydLZvjXgq74LL+TtAA9eypsR3/5a0eU y4+j5aY9f0/ThfoxKFNiz8hAqlSS71PzdB0CvOBkWkPqSuH32hZx2weYoTJJHzYJZolV bhDRgc3o4qc3gXsDZI+sTK8RXbCsXsvuB9IqDgEtUwUhwMlCDzqwOu5ZazYh7QlorC4e Rf6fXQKm6Ze1otaHAtF77DWu6Or3D/F8a0B4ghgcuYO9Jj+2JLFE71LOCJLJf9b5aM3c XorEvao0Q649HzXZFbAptMnAUpo96UcdnX8XRrxFstRWwTrhp1t0YdO6ldmttivTBOLI gC7w== X-Forwarded-Encrypted: i=1; AJvYcCXVCSWVobZSC1g91YEsoe6lQ/n08qqIBdYUnVPhcDOQmovIYchnowZdua3yK3lUoXGGqbat3xepOJbSOuiw/pirQbt3pw0jOQjT X-Gm-Message-State: AOJu0YyTHKuhteJT6/8IsQxYXWpjnh7fJzN/VQVsA9DZxQ7uJZU+8LJf Zld++PWKSDQDwTiHukOJ2QIdcinQFxYPT/fu6At6v8IUKVB/ONolTZucYpNieUCds4/P1yXSCrB O0jW1lSXyl+rcPz3gNiyaEKyCt0ro4gqvyCB8Lu1gq+nMrUmuGuxPDHpUQQ== X-Received: by 2002:a05:6000:1942:b0:368:3038:8290 with SMTP id ffacd0b85a97d-36b36421ac8mr707599f8f.39.1721886860525; Wed, 24 Jul 2024 22:54:20 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHI3Abal444WmsilGMojUOB9llheQDVQUaMgG30HCOZkmwXntXo9Fy/JkeXGpR8m6xgr9AF9A== X-Received: by 2002:a05:6000:1942:b0:368:3038:8290 with SMTP id ffacd0b85a97d-36b36421ac8mr707561f8f.39.1721886859582; Wed, 24 Jul 2024 22:54:19 -0700 (PDT) Received: from redhat.com ([2a02:14f:1ed:8427:35e3:731c:3106:ee46]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-36b36857dcesm900105f8f.85.2024.07.24.22.54.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Jul 2024 22:54:18 -0700 (PDT) Date: Thu, 25 Jul 2024 01:54:10 -0400 From: "Michael S. Tsirkin" To: David Woodhouse Cc: Richard Cochran , Peter Hilber , linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-rtc@vger.kernel.org, "Ridoux, Julien" , virtio-dev@lists.linux.dev, "Luu, Ryan" , "Chashper, David" , "Mohamed Abuelfotoh, Hazem" , "Christopher S . Hall" , Jason Wang , John Stultz , netdev@vger.kernel.org, Stephen Boyd , Thomas Gleixner , Xuan Zhuo , Marc Zyngier , Mark Rutland , Daniel Lezcano , Alessandro Zummo , Alexandre Belloni , qemu-devel , Simon Horman Subject: Re: [PATCH] ptp: Add vDSO-style vmclock support Message-ID: <20240725015120-mutt-send-email-mst@kernel.org> References: <14d1626bc9ddae9d8ad19d3c508538d10f5a8e44.camel@infradead.org> Precedence: bulk X-Mailing-List: linux-rtc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <14d1626bc9ddae9d8ad19d3c508538d10f5a8e44.camel@infradead.org> On Wed, Jul 24, 2024 at 06:16:37PM +0100, David Woodhouse wrote: > From: David Woodhouse > > The vmclock "device" provides a shared memory region with precision clock > information. By using shared memory, it is safe across Live Migration. > > Like the KVM PTP clock, this can convert TSC-based cross timestamps into > KVM clock values. Unlike the KVM PTP clock, it does so only when such is > actually helpful. > > The memory region of the device is also exposed to userspace so it can be > read or memory mapped by application which need reliable notification of > clock disruptions. > > Signed-off-by: David Woodhouse one other thing worth mentioning is that this design can't work with confidential computing setups. By comparison, mapping e.g. a range in a PCI BAR would work for these setups. Is there a reason this functionality is not interesting for confidential VMs? -- MST