[PATCH v7 0/5] misc fixes to PV extensions code

[Zhenzhong Duan]

Hi,

In virtualization environment, PV extensions (drivers, interrupts,
timers, etc) are enabled in the majority of use cases which is the
best option.

However, in some cases (kexec not fully working, benchmarking, etc)
we want to disable PV extensions. We have xen_nopv for that purpose
but only for XEN. For a consistent admin experience a common command
line parameter set across all PV guest implementations is a better
choice.

To achieve this introduce a new 'nopv' parameter which is usable by
most of PV guest implementation. Due to the limitation of some PV
guests(XEN PV, XEN PVH and jailhouse), 'nopv' is ignored for XEN PV
, jailhouse and XEN PVH if booting via Xen-PVH boot entry. If booting
via normal boot entry(like grub2), PVH guest has to panic itself
currently.

While analyzing the PV guest code one bug were found and fixed.
(Patches 1). It can be applied independent of the functional
changes, but is kept in the series as the functional changes
depend on them.

For compatibility reason, "xen_nopv" is keeped and mapped to "nopv",
this way also avoids an issue with xen_nopv when booting PVH guest.

Build test passes with CONFIG_HYPERVISOR_GUEST enable and disabled.
I didn't get env to test with jailhouse and Hyperv, the others work
as expected.

v7:
PATCH4 a new added patch prerequite for PATCH5(previously PATCH4)
PATCH5 rewrite the code based on Boris's suggestion. I compare the one
to update interface function one-by-one and the one to modify all
x86_hyper_xen_hvm's ops to immediately return if nopv is set, both
have same effect and the first looks smarter, so choose the 1st one.

v6:
PATCH3 add Reviewed-by
PATCH4 remove unnecessory xen_hvm_nopv_guest_late_init() per Boris

v5:
PATCH2:
update patch description per Boris
add declaration of nopv variable in arch/x86/include/asm/hypervisor.h
which will be used in PATCH3 and PATCH4

PATCH3 update xen_parse_nopv() per Boris
PATCH4 add nopv=false per Boris
Combine PATCH5 into PATCH3


v4:
PATCH5 a new patch to add 'xen_nopv' back per Boris

v3:
Remove some unrelated patches from patchset as suggested by Tglx

PATCH1 unchanged
PATCH2 add Reviewed-by
PATCH3 add Reviewed-by
PATCH4 rewrite the patch as Jgross found an issue in old patch,
description is also updated.

v2:
PATCH3 use 'ignore_nopv' for PVH/PV guest as suggested by Jgross.
PATCH5 new added one, specifically for HVM guest

Thanks
Zhenzhong