[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] RFC: making the PVH 64bit ABI as stableo
On 06/03/2015 05:03 AM, Ian Campbell wrote: On Tue, 2015-06-02 at 13:12 -0400, Boris Ostrovsky wrote:On 06/02/2015 12:51 PM, Stefano Stabellini wrote:On Tue, 2 Jun 2015, Jan Beulich wrote:On 02.06.15 at 17:11, <roger.pau@xxxxxxxxxx> wrote:Hello, The document describing the PVH interface was committed 9 months ago [1], and since then there hasn't been any change regarding the interface. PVH is still missing features in order to have feature parity with pure PV, mainly: - DomU miration support. - PCI passthrough support. - 32bit support. - AMD support. AFAICT however none of these features are going to change the current ABI.This your guess; I don't think there's any guarantee.Let's make it a guarantee.The more that talk was about making PVH uniformly enter the kernel in 32-bit mode.What talk? IRL talks are irrelevant in this context. If it is not on the list, it doesn't exist.PCI passthrough might expand it, by adding new hypercalls, but I don't think this should prevent us from marking the current ABI as stable. ARM for example doesn't have PCI passthrough yet or migration support, but the ABI has been marked as stable. To that end, I would like to request the 64bit PVH ABI to be marked as stable for DomUs. This is needed so external projects (like PVH support for grub2) can progress.Understandable, but no, not before all the fixmes in the tree got dealt with.What is your timeline for that? In fact does anybody have any timelines for it? We need to have a clear idea of what exactly needs to happen. We also need to have confidence that is going to happen in a reasonable time frame. At the moment we have some various mumblings about things, but we don't have a clear breakdown of the outstanding work and names associated with each work item. Is anybody going to volunteer writing that todo list? Are we going to be able to find enough volunteers with the right skills to be confident that PVH is going to be out of "experimental" within a reasonable time frame? It is clear that some of the clean-ups require an hypervisor expert. If not, I suggest we rethink our priorities and we consider dropping PVH entirely. I don't think is fair to expect Roger or anybody else to keep their efforts up on PVH, when actually we don't know if we'll be able to land it.Roger, Tim, Elena, Konrad and I had a conversation a few months ago and at that time we came up with a (somewhat informal) list of what we knew was broken: - 32-bit cannot boot. - Does not work under AMD. - Migration - PCI passthrough - Memory ballooning - Multiple VBDs, NICs, etc. - CPUID filtering. There are no filtering done at all which means that certain cpuid flags are exposed to the guest. - The x2apic will cause a crash if the NMI handler is invoked. - The APERF will cause inferior scheduling decisions. - working with shadow code (which is what we use when migrating HVM guests). But the nice side-benefit is that we can then run PVH on machines without VMX or SVM support. - TSC modes are broken.This is missing at least: - Remove all /* pvh fixme */ from the code I considered those would be gone as part of working out the item on the list above (I know that many, if not most, of them are for 32-bit guests and I removed them in my semi-working tree) What I'm hearing from the x86 maintainers is that this is actually a high priority and not a "nice to have cleanup".I picked 32-bit support, Elena is looking into AMDWith the TODOs + these 2 being the things which the x86 maintainers have highlighted in this thread as being most critical for marking the ABI as stable (or at least moving experimental->tech preview) let me ask explicotly: What are the current time frames on these two items? For 32-bit support, just to get it to work in the within current framework I think can be done for 4.7 release (which is late this year IIRC). I can't tell you how much it will take to make it a part of a "unified" 32/64-bit guest launching as I haven't looked at this at all yet. -boris _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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