linux-kernel - [PATCH v5 0/5] 86/paravirt: Get rid of paravirt patching

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Message-Id: <20231129133332.31043-1-jgross@suse.com>
Date:   Wed, 29 Nov 2023 14:33:27 +0100
From:   Juergen Gross <jgross@...e.com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org,
        virtualization@...ts.linux.dev, kvm@...r.kernel.org
Cc:     Juergen Gross <jgross@...e.com>, Ajay Kaher <akaher@...are.com>,
        Alexey Makhalov <amakhalov@...are.com>,
        VMware PV-Drivers Reviewers <pv-drivers@...are.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        xen-devel@...ts.xenproject.org
Subject: [PATCH v5 0/5] 86/paravirt: Get rid of paravirt patching

This is a small series getting rid of paravirt patching by switching
completely to alternative patching for the same functionality.

The basic idea is to add the capability to switch from indirect to
direct calls via a special alternative patching option.

This removes _some_ of the paravirt macro maze, but most of it needs
to stay due to the need of hiding the call instructions from the
compiler in order to avoid needless register save/restore.

What is going away is the nasty stacking of alternative and paravirt
patching and (of course) the special .parainstructions linker section.

I have tested the series on bare metal and as Xen PV domain to still
work.

Note that objtool might need some changes to cope with the new
indirect call patching mechanism. Additionally some paravirt handling
can probably be removed from it.

Changes in V5:
- addressed Boris' comments
- rebased on top of the tip/master branch

Changes in V4:
- addressed Boris' comments in patch 1
- fixed bugs found by kernel test robot (patch 2)

Changes in V3:
- split v2 patch 3 into 2 patches as requested by Peter and Ingo

Changes in V2:
- split last patch into 2
- rebase of patch 2 as suggested by Peter
- addressed Peter's comments for patch 3

Juergen Gross (5):
  x86/paravirt: introduce ALT_NOT_XEN
  x86/paravirt: move some functions and defines to alternative
  x86/alternative: add indirect call patching
  x86/paravirt: switch mixed paravirt/alternative calls to alternative_2
  x86/paravirt: remove no longer needed paravirt patching code

 arch/x86/include/asm/alternative.h        |  30 +++++-
 arch/x86/include/asm/paravirt.h           |  77 ++++---------
 arch/x86/include/asm/paravirt_types.h     |  85 +++++----------
 arch/x86/include/asm/qspinlock_paravirt.h |   4 +-
 arch/x86/include/asm/text-patching.h      |  12 ---
 arch/x86/kernel/alternative.c             | 125 ++++++++++------------
 arch/x86/kernel/callthunks.c              |  17 ++-
 arch/x86/kernel/kvm.c                     |   4 +-
 arch/x86/kernel/module.c                  |  20 +---
 arch/x86/kernel/paravirt.c                |  54 ++--------
 arch/x86/kernel/vmlinux.lds.S             |  13 ---
 arch/x86/tools/relocs.c                   |   2 +-
 arch/x86/xen/irq.c                        |   2 +-
 13 files changed, 161 insertions(+), 284 deletions(-)

-- 
2.35.3