linux-kernel - Re: [RFC PATCH 0/3] x86/paravirt: Get rid of paravirt patching

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Date:   Mon, 10 Jul 2023 14:29:28 +0200
From:   Juergen Gross <jgross@...e.com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org
Cc:     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>,
        "Srivatsa S. Bhat (VMware)" <srivatsa@...il.mit.edu>,
        Alexey Makhalov <amakhalov@...are.com>,
        VMware PV-Drivers Reviewers <pv-drivers@...are.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: Re: [RFC PATCH 0/3] x86/paravirt: Get rid of paravirt patching

Any comments?

On 08.06.23 16:03, Juergen Gross wrote:
> 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.
> 
> RFC because I'm quite sure there will be some objtool work needed
> (at least removing the specific paravirt handling).
> 
> Juergen Gross (3):
>    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
> 
>   arch/x86/include/asm/alternative.h        | 26 +++++-
>   arch/x86/include/asm/paravirt.h           | 39 ++-------
>   arch/x86/include/asm/paravirt_types.h     | 68 +++-------------
>   arch/x86/include/asm/qspinlock_paravirt.h |  4 +-
>   arch/x86/include/asm/text-patching.h      | 12 ---
>   arch/x86/kernel/alternative.c             | 99 +++++++++++------------
>   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, 111 insertions(+), 249 deletions(-)
> 


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