linux-kernel - Re: [PATCH 02/22] x86/srso: Set CPUID feature bits independently of bug or mitigation status

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Message-ID: <20230821135957.GAZONt3W2U/krVX9jH@fat_crate.local>
Date:   Mon, 21 Aug 2023 15:59:57 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Josh Poimboeuf <jpoimboe@...nel.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Babu Moger <babu.moger@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>, David.Kaplan@....com,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Nikolay Borisov <nik.borisov@...e.com>,
        gregkh@...uxfoundation.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 02/22] x86/srso: Set CPUID feature bits independently of
 bug or mitigation status

On Sun, Aug 20, 2023 at 06:18:59PM -0700, Josh Poimboeuf wrote:
> Booting with mitigations=off incorrectly prevents the
> X86_FEATURE_{IBPB_BRTYPE,SBPB} CPUID bits from getting set.
> 
> Also, future CPUs without X86_BUG_SRSO might still have IBPB with branch
> type prediction flushing, in which case SBPB should be used instead of
> IBPB.  The current code doesn't allow for that.
> 
> Also, cpu_has_ibpb_brtype_microcode() has some surprising side effects
> and the setting of these feature bits really doesn't belong in the
> mitigation code anyway.  Move it to earlier.
> 
> Fixes: fb3bd914b3ec ("x86/srso: Add a Speculative RAS Overflow mitigation")
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> ---
>  arch/x86/include/asm/processor.h |  2 --
>  arch/x86/kernel/cpu/amd.c        | 28 +++++++++-------------------
>  arch/x86/kernel/cpu/bugs.c       | 13 +------------
>  3 files changed, 10 insertions(+), 33 deletions(-)

Reviewed-by: Borislav Petkov (AMD) <bp@...en8.de>

-- 
Regards/Gruss,
    Boris.

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