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[66.187.233.206]) by smtp.gmail.com with ESMTPSA id k185-v6sm6266398qkd.27.2018.10.26.10.00.53 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 26 Oct 2018 10:00:54 -0700 (PDT) Subject: Re: [Patch v3 04/13] x86/speculation: Disable STIBP when enhanced IBRS is in use To: Tim Chen , Jiri Kosina , Thomas Gleixner Cc: Tom Lendacky , Ingo Molnar , Peter Zijlstra , Josh Poimboeuf , Andrea Arcangeli , David Woodhouse , Andi Kleen , Dave Hansen , Casey Schaufler , Asit Mallick , Arjan van de Ven , Jon Masters , linux-kernel@vger.kernel.org, x86@kernel.org References: From: Waiman Long Message-ID: <43c23fc3-ebaa-fe7c-f7b7-54a5166b6b49@gmail.com> Date: Fri, 26 Oct 2018 13:00:52 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/17/2018 01:59 PM, Tim Chen wrote: > With enhanced IBRS in use, the application running on sibling CPU will not > be able to launch Spectre v2 attack to the application on current CPU. > There is no need to use STIBP for this case. Disable the STIBP code > when enhanced IBRS is used. > > Signed-off-by: Tim Chen > --- > arch/x86/kernel/cpu/bugs.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c > index 2fc7b4e..6ed82ea 100644 > --- a/arch/x86/kernel/cpu/bugs.c > +++ b/arch/x86/kernel/cpu/bugs.c > @@ -327,6 +327,14 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void) > > static bool stibp_needed(void) > { > + /* > + * Determine if we want to leave STIBP always on. > + * Using enhanced IBRS makes using STIBP unnecessary. > + */ > + > + if (static_branch_unlikely(&spectre_v2_enhanced_ibrs)) > + return false; > + > if (spectre_v2_enabled == SPECTRE_V2_NONE) > return false; > > @@ -881,7 +889,9 @@ static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr > ", IBPB" : "", > boot_cpu_has(X86_FEATURE_USE_IBRS_FW) ? > ", IBRS_FW" : "", > - (x86_spec_ctrl_base & SPEC_CTRL_STIBP) ? > + spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED ? > + ", Enhanced IBRS" : > + (x86_spec_ctrl_base & SPEC_CTRL_STIBP) ? > ", STIBP" : "", > boot_cpu_has(X86_FEATURE_RSB_CTXSW) ? > ", RSB filling" : "", The "Enhanced IBRS" is one of the states of spectre_v2_enabled. So you don't need to print that out one more time. Cheers, Longman