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Thanks for the interesting reply. These are fair points. And I hadn't considered the Citrix products. If you read this then I do have another question. Is there

by als0 6y ago

Thanks for the interesting reply. These are fair points. And I hadn't considered the Citrix products. If you read this then I do have another question. Is there way to disable PV guest support in Xen? IIRC this code represented a good portion of Xen's CVE list. It is an attack surface that we no longer need on modern CPUs. In theory you can just never run a PV guest but the code would still be present?

gwd 6y ago
TLDR: Yes, you can disable PV entirely on x86 systems; on ARM systems, there never was PV. On x86, as you say, has "classic" Xen PV, which doesn't require virtualization extensions. It also has "HVM", which includes a full system emulation (motherboard, etc); but also "PVH", which is basically what PV would be if it were designed today: It takes advantage of hardware support when it makes sense, and paravirtualizes when it makes sense. It doesn't require a devicemodel to be running at all, but also isn't susceptible to the PV XSAs. There's also a mode called "shim" mode, which allows you to run "classic PV" kernels in PVH mode. Xen now has KConfig, and you can now disable PV mode entirely when building Xen. You can run dom0 in PVH mode, and then run all of your guests either in PVH mode or HVM mode. The ARM port was made after ARM had virtualization extensions; so it never had a "classic PV"; nor does it require any devicemodel whatsoever. There's only one guest mode, which corresponds roughly to the "PVH" mode above.