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Date:   Thu, 14 Jul 2022 19:00:05 -0700
From:   Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
To:     Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org,
        Daniel Sneddon <daniel.sneddon@linux.intel.com>,
        antonio.gomez.iglesias@linux.intel.com,
        Josh Poimboeuf <jpoimboe@kernel.org>
Subject: Re: [PATCH v2] x86/bugs: Warn when "ibrs" mitigation is selected on
 Enhanced IBRS parts
Message-ID: <20220715020005.dixdi3qpb23iz6up@desk>
References: <0456b35fb9ef957d9a9138e0913fb1a3fd445dff.1657747493.git.pawan.kumar.gupta@linux.intel.com>
 <2a5eaf54583c2bfe0edc4fea64006656256cca17.1657814857.git.pawan.kumar.gupta@linux.intel.com>
 <YtCwpjeRVu4LVOyF@quatroqueijos>
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On Thu, Jul 14, 2022 at 09:11:18PM -0300, Thadeu Lima de Souza Cascardo wrote:
>On Thu, Jul 14, 2022 at 04:15:35PM -0700, Pawan Gupta wrote:
>> IBRS mitigation for spectre_v2 forces write to MSR_IA32_SPEC_CTRL at
>> every kernel entry/exit. On Enhanced IBRS parts setting
>> MSR_IA32_SPEC_CTRL[IBRS] only once at boot is sufficient. MSR writes at
>> every kernel entry/exit incur unnecessary performance loss.
>>
>> When Enhanced IBRS feature is present, print a warning about this
>> unnecessary performance loss.
>>
>> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
>
>Reviewed-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

Thanks for the review.

Pawan