linux-kernel - Re: [RFC][PATCH 07/17] x86/cpu/kvm: Provide UNTRAIN_RET

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Message-ID: <20230809135004.2xy76kqpptfqxsp5@treble>
Date:   Wed, 9 Aug 2023 09:50:04 -0400
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, David.Kaplan@....com,
        Andrew.Cooper3@...rix.com, gregkh@...uxfoundation.org
Subject: Re: [RFC][PATCH 07/17] x86/cpu/kvm: Provide UNTRAIN_RET_VM

On Wed, Aug 09, 2023 at 09:12:25AM +0200, Peter Zijlstra wrote:
> With the difference being that UNTRAIN_RET_VM uses
> X86_FEATURE_IBPB_ON_VMEXIT instead of X86_FEATURE_ENTRY_IBPB.
> 
> This cures VMEXIT doing potentially unret+IBPB or double IBPB.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  arch/x86/include/asm/nospec-branch.h |   11 +++++++++++
>  arch/x86/kernel/cpu/bugs.c           |   17 ++++++++++++++++-
>  arch/x86/kvm/svm/vmenter.S           |    7 ++-----
>  3 files changed, 29 insertions(+), 6 deletions(-)
> 
> --- a/arch/x86/include/asm/nospec-branch.h
> +++ b/arch/x86/include/asm/nospec-branch.h
> @@ -299,6 +299,17 @@
>  #endif
>  .endm
>  
> +.macro UNTRAIN_RET_VM
> +#if defined(CONFIG_CPU_UNRET_ENTRY) || defined(CONFIG_CPU_IBPB_ENTRY) || \
> +	defined(CONFIG_CALL_DEPTH_TRACKING) || defined(CONFIG_CPU_SRSO)

Maybe can be simplified?

#if defined(CONFIG_RETHUNK) || defined(CONFIG_CPU_IBPB_ENTRY)

-- 
Josh