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

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Message-ID: <20230813103657.GCZNiySRVa8TcT7SAW@fat_crate.local>
Date:   Sun, 13 Aug 2023 12:36:57 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, David.Kaplan@....com,
        Andrew.Cooper3@...rix.com, jpoimboe@...nel.org,
        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.

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);


But I like the separate macro.

-- 
Regards/Gruss,
    Boris.

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