From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 BED0917A92F for ; Fri, 26 Jul 2024 13:04:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721999092; cv=none; b=mkx0K7HWxNxmdB7wYRi0FXMtB6d780qx97XChE456uiKRLW1odCQhcQJlFkE6sM9/CyatFMQumtCjo4Ads/Lh9Ju30iBpofhL5m15cDcGn4dG7zsJLHzVlSSgbW/0T0a/79/nk4FpSYLIaL+/Kjhaar8Z6cUq2UVgk1cQWRJOFc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721999092; c=relaxed/simple; bh=uO12G0ckq47fIdqtlyWIWsBBD7gHquBqgoUXT4gDyT0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=DtQGZfI7ERXqf/iKgUFXJih2Hcq0XYGp3ws44tMrYmqXk8exutfAb4tspnlXWt1XsNXIUirbDqYXyN66soN24XsEf6gQW9eb6m7IMv0+JbiLZfWcq1pcv+0Vw791Me6/m1+qGlGorOmSOgnvTmnJ4T+DP7KDfz5/eOk5MKU5Fbw= 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=RyaflvMl; arc=none smtp.client-ip=170.10.129.124 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="RyaflvMl" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1721999089; 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=B3g6QURrGZPYRxDC3Hx/i8519mXf108ro6Hrgt5KPqY=; b=RyaflvMlkp9q9U9vkTVYZHyYhNQ9E70HW9g3yCMmoNczBVFydqCP6jXiJ93/N5mLUT7pRu css/8kzPhXPywve/aXIwM8hjnloj7CeYNA5VgpX9A8Kx0aDF404B6ogOw1tPMH25xXFnZu ML/rrX7TJS+bLXiZXGUilAVYgSjkKAA= Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-203-Jj0Ub-4HPg2sdYjAjjFutg-1; Fri, 26 Jul 2024 09:04:48 -0400 X-MC-Unique: Jj0Ub-4HPg2sdYjAjjFutg-1 Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-426624f4ce3so14165585e9.1 for ; Fri, 26 Jul 2024 06:04:48 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1721999087; x=1722603887; 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=B3g6QURrGZPYRxDC3Hx/i8519mXf108ro6Hrgt5KPqY=; b=cGOSkpfbE45OI+QCWBUaL0COHJeNBD3Wr0wVDjZcXF10CH6iTj1T5Wk/acapggx+b6 +xLZgnWJH8E4SxZ5UNQXtqH+gh7ClmXN7CfD9D7+xurJtr03h9SlQHYFf8zPscnNjcN9 nsS6A9wewKSXgnhHK3gZaCt4d1PrbJ0GEK7C2e/BUWYP1t88HaCdBWhqAXU60O0XlXf0 o4WrYIe+YdtdRC5E/YG7mt79SyNcmxTRruzzUpdvyibTlRpssJYBizRsU3ACuiYqJ0JY RTDyt4ZMSJKTXENUgn8hMN6G/CXrXUG0ZWPODBqKWjyluHIycOILrw5X26YTt2c0yXCI GBRQ== X-Forwarded-Encrypted: i=1; AJvYcCUX/wMeJu0rOjnZk+jv4EXRb8GcSK1SwEkTCLG+K0ur25TWkoWUH8EFK5ZQfJpm6GJHf1mY40Tb2dBTkg2CunrasmjPsfGxBwRB X-Gm-Message-State: AOJu0Yyx7mXW3/ctMXBxfMFzl/bik6H+6Fe+OlBpgPJuZmVKaBsez/i+ htPRs8Y6qEKRg8S/jKEXKlZB+EIeqmMOY82UqCGPD/vSQB/6SKCm44OBbJsCZGFhW8uEqocu4ay iBwUuFD+edvFi9PCs3MYHIgj8pfQ0SNFcxslY5fWo9zJ1UzAqiSii+TxF2Q== X-Received: by 2002:adf:f40e:0:b0:368:4ed7:2acc with SMTP id ffacd0b85a97d-36b3638148cmr3751290f8f.5.1721999087365; Fri, 26 Jul 2024 06:04:47 -0700 (PDT) X-Google-Smtp-Source: AGHT+IE2baiiVUKUBh/QT4ya/E9LOG3bE0mPK5t7EPOeVJPpQaN0mCePZ4SEB2ju0LD0SShA7ME5CA== X-Received: by 2002:adf:f40e:0:b0:368:4ed7:2acc with SMTP id ffacd0b85a97d-36b3638148cmr3751249f8f.5.1721999086564; Fri, 26 Jul 2024 06:04:46 -0700 (PDT) Received: from redhat.com ([2a02:14f:1f7:28ce:f21a:7e1e:6a9:f708]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-36b36801828sm5090963f8f.65.2024.07.26.06.04.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 26 Jul 2024 06:04:46 -0700 (PDT) Date: Fri, 26 Jul 2024 09:04:38 -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: <20240726090326-mutt-send-email-mst@kernel.org> References: <20240725163843-mutt-send-email-mst@kernel.org> <20240725170328-mutt-send-email-mst@kernel.org> <20240725174327-mutt-send-email-mst@kernel.org> <9261e393083bcd151a017a5af3345a1364b3e0f3.camel@infradead.org> <20240726015613-mutt-send-email-mst@kernel.org> <2e427b102d8fd899a9a3db2ec17a628beb24bc01.camel@infradead.org> <20240726084836-mutt-send-email-mst@kernel.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: On Fri, Jul 26, 2024 at 02:00:25PM +0100, David Woodhouse wrote: > On Fri, 2024-07-26 at 08:52 -0400, Michael S. Tsirkin wrote: > > On Fri, Jul 26, 2024 at 09:35:51AM +0100, David Woodhouse wrote: > > > But for this use case, we only need a memory region that the hypervisor > > > can update. We don't need any of that complexity of gratuitously > > > interrupting all the vCPUs just to ensure that none of them can be > > > running userspace while one of them does an update for itself, > > > potentially translating from one ABI to another. The hypervisor can > > > just update the user-visible memory in place. > > > > Looks like then your userspace is hypervisor specific, and that's a > > problem because it's a one way street - there is no way for hypervisor > > to know what does userspace need, so no way for hypervisor to know which > > information to provide. No real way to fix bugs. > > It's not hypervisor specific, but you're right that as it stands there > is no negotiation of what userspace wants. So the hypervisor provides > what it feels it can provide without significant overhead (which may or > may not include the precise timekeeping, as discussed, but should > always include the disruption signal which is the most important > thing). > > The guest *does* know what the hypervisor provides. And when we get to > do this in virtio, we get all the goodness of negotiation as well. The > existence of the simple ACPI model doesn't hurt that at all. Maybe it doesn't, at that. E.g. virtio does a copy, acpi doesn't? I'll ponder compatibility over the weekend. -- MST