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Date:   Mon, 14 Aug 2023 12:35:27 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Borislav Petkov <bp@alien8.de>
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org, David.Kaplan@amd.com,
        Andrew.Cooper3@citrix.com, jpoimboe@kernel.org,
        gregkh@linuxfoundation.org
Subject: Re: [RFC][PATCH 07/17] x86/cpu/kvm: Provide UNTRAIN_RET_VM
Message-ID: <20230814103527.GD776869@hirez.programming.kicks-ass.net>
References: <20230809071218.000335006@infradead.org>
 <20230809072200.922634286@infradead.org>
 <20230813103657.GCZNiySRVa8TcT7SAW@fat_crate.local>
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On Sun, Aug 13, 2023 at 12:36:57PM +0200, Borislav Petkov wrote:
> 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.
> 
> Can't - I have a separate flag for that and I set it only when !IBPB:
> 
>         case SRSO_CMD_IBPB_ON_VMEXIT:
>                 if (IS_ENABLED(CONFIG_CPU_SRSO)) {
>                         if (!boot_cpu_has(X86_FEATURE_ENTRY_IBPB) && has_microcode) {
>                                 setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
> 

Of course you can, just also set it with regular IBPB :-)