Eliminate the usergs_sysret64 paravirt call completely and switch
the swapgs one to use ALTERNATIVE instead. This requires to fix the
IST based exception entries for Xen PV to use the same mechanism as
NMI and debug exception already do.

Juergen Gross (4):
  x86/xen: use specific Xen pv interrupt entry for MCE
  x86/xen: use specific Xen pv interrupt entry for DF
  x86/pv: switch SWAPGS to ALTERNATIVE
  x86/xen: drop USERGS_SYSRET64 paravirt call

 arch/x86/entry/entry_64.S             | 32 ++++++++++++---------------
 arch/x86/include/asm/idtentry.h       |  6 +++++
 arch/x86/include/asm/irqflags.h       | 26 +++++++---------------
 arch/x86/include/asm/paravirt.h       | 25 ---------------------
 arch/x86/include/asm/paravirt_types.h | 10 ---------
 arch/x86/kernel/asm-offsets_64.c      |  3 ---
 arch/x86/kernel/paravirt.c            |  6 +----
 arch/x86/kernel/paravirt_patch.c      |  7 ------
 arch/x86/xen/enlighten_pv.c           | 28 ++++++++++++++++++-----
 arch/x86/xen/xen-asm.S                | 24 ++------------------
 arch/x86/xen/xen-ops.h                |  2 --
 11 files changed, 53 insertions(+), 116 deletions(-)

-- 
2.26.2

On Mon, Nov 16, 2020 at 04:22:57PM +0100, Juergen Gross wrote:
> Eliminate the usergs_sysret64 paravirt call completely and switch
> the swapgs one to use ALTERNATIVE instead. This requires to fix the
> IST based exception entries for Xen PV to use the same mechanism as
> NMI and debug exception already do.
> 
> Juergen Gross (4):
>   x86/xen: use specific Xen pv interrupt entry for MCE
>   x86/xen: use specific Xen pv interrupt entry for DF
>   x86/pv: switch SWAPGS to ALTERNATIVE
>   x86/xen: drop USERGS_SYSRET64 paravirt call

Looks 'sane' :-))

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>