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Date:   Wed, 9 Aug 2023 09:50:04 -0400
From:   Josh Poimboeuf <jpoimboe@kernel.org>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org, David.Kaplan@amd.com,
        Andrew.Cooper3@citrix.com, gregkh@linuxfoundation.org
Subject: Re: [RFC][PATCH 07/17] x86/cpu/kvm: Provide UNTRAIN_RET_VM
Message-ID: <20230809135004.2xy76kqpptfqxsp5@treble>
References: <20230809071218.000335006@infradead.org>
 <20230809072200.922634286@infradead.org>
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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@infradead.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