[PATCH 0/3] x86/pv: Multiple fixes to SYSCALL/SYSENTER handling (XSA-339 followup)

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Patches 1 and 2 are a consequence of trying to get the Linux x86 selftests to
pass even when running under Xen.

Patches 3 and XSA-339 were further fallout from trying to put in place testing
to cover all aspects of the PV fast system call entrypoints.

Patch 3 was almost an XSA itself, but was ultimately argued as not affecting
any known PV guest.  It turns out that this is only true because of c/s
dba899de14 in 2018, which did fix a real userspace => VM DoS on NetBSD.

All fixes need backporting.

Andrew Cooper (3):
  x86/pv: Don't deliver #GP for a SYSENTER with NT set
  x86/pv: Don't clobber NT on return-to-guest
  x86/pv: Inject #UD for missing SYSCALL callbacks

 xen/arch/x86/x86_64/compat/entry.S |  2 +-
 xen/arch/x86/x86_64/entry.S        | 31 +++++++++++++++++++++----------
 2 files changed, 22 insertions(+), 11 deletions(-)

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2.11.0