[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH RFC v13 03/20] Introduce pv guest type and has_hvm_container macros
On Thu, Sep 26, 2013 at 02:46:04PM +0100, George Dunlap wrote: > On 26/09/13 12:53, Tim Deegan wrote: > >Hi, > > > >At 17:49 +0100 on 23 Sep (1379958583), George Dunlap wrote: > >>The goal of this patch is to classify conditionals more clearly, as to > >>whether they relate to pv guests, hvm-only guests, or guests with an > >>"hvm container" (which will eventually include PVH). > > - speculative wombling begins - > > > >Reading this for the (apparently) 13th time, it strikes me that this > >distinction feels wrong, like entities are being multiplied beyond > >necessity. > > > >A PVH guest is basically a HVM guest that starts with paging enabled and > >uses event channel instead of virtual APIC. > > > >I'm not sure this needs any special treatment from Xen. We can supply a > >PVH guest with an APIC and if it never uses it, fine. And we can supply > >all HVM guests with any extra hypercalls that PVH needs (for vcpu > >bringup &c). Things like not having a qemu process to serve ioreqs can > >be arranged by the toolstack. > > > >This is from a position of ignorance, of course, and I'm happy to be > >corrected by the people who've actually been hacking on the code. > > As I've been putting the series together, I've wondered the same myself. > > There's more to not having a qemu than just not starting qemu, of > course; a lot of the HVM codepaths assume that there is one and will > dereference structures which will be empty. But that should be > fairly easy to fix. > > Having the PV e820 map makes sense, but you can file that under > "make available to hvm guests as well". Which I think Mr. Gordon (sp?) had been doing for some of the PCI NVidia passthrough stuff. Basically making e820_host work for HVM guests. > > The main things left are the PV paths for cpuid, PIO, and forced > emulated ops. I haven't taken a close look at how these differ, or > what benefit is gained from using the PV version over the HVM > version. > > The other big thing is being able to set up more state when bringing > up a vcpu. > > One reason to disable unneeded things is the security angle: there > is a risk, no matter how small, that there is somehow an exploitable > bug in our emulated APIC / PIT code; so running with the code > entirely disabled is more secure than running with it enabled but > just not used. > > But it's possible that we could just add a few options to the > existing "HVM mode" that would implement all of this. > > -George > > _______________________________________________ > Xen-devel mailing list > Xen-devel@xxxxxxxxxxxxx > http://lists.xen.org/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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