From: Borislav Petkov <bp@alien8.de>
To: Maxim Levitsky <mlevitsk@redhat.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
Ingo Molnar <mingo@redhat.com>,
Josh Poimboeuf <jpoimboe@kernel.org>,
Namhyung Kim <namhyung@kernel.org>,
Tony Luck <tony.luck@intel.com>,
Paolo Bonzini <pbonzini@redhat.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Tim Chen <tim.c.chen@linux.intel.com>,
"David S. Miller" <davem@davemloft.net>,
Dave Hansen <dave.hansen@linux.intel.com>,
"Chang S. Bae" <chang.seok.bae@intel.com>,
Jane Malalane <jane.malalane@citrix.com>,
Kees Cook <keescook@chromium.org>,
Kan Liang <kan.liang@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>, Herbert Xu <herbert@gondor.apana.org.au>,
Jiri Olsa <jolsa@kernel.org>, Mark Rutland <mark.rutland@arm.com>,
linux-perf-users@vger.kernel.org,
"open list:CRYPTO API" <linux-crypto@vger.kernel.org>
Subject: Re: [PATCH v2 1/5] perf/x86/intel/lbr: use setup_clear_cpu_cap instead of clear_cpu_cap
Date: Mon, 26 Sep 2022 15:12:32 +0200 [thread overview]
Message-ID: <YzGlQBkCSJxY+8Jf@zn.tnic> (raw)
In-Reply-To: <c105971a72dfe6d46ad75fb7e71f79ba716e081c.camel@redhat.com>
On Tue, Sep 20, 2022 at 11:20:47AM +0300, Maxim Levitsky wrote:
> If I understand that correctly, the difference between clear_cpu_cap and setup_clear_cpu_cap
> is that setup_clear_cpu_cap should be called early when only the boot cpu is running and it
>
> 1. works on 'boot_cpu_data' which represents the boot cpu.
> 2. sets a bit in 'cpu_caps_cleared' which are later applied to all CPUs, including these that are hotplugged.
Yes.
> On the other hand the clear_cpu_cap just affects the given 'struct cpuinfo_x86'.
Yes.
> Call of 'clear_cpu_cap(&boot_cpu_data, X86_FEATURE_ARCH_LBR)' is weird since it still affects 'boot_cpu_data'
> but doesn't affect 'cpu_caps_cleared'
Yes.
> I assumed that this was a mistake and the intention was to disable the feature on all CPUs.
peterz says yes.
> I need this patch because in the next patch, I change the clear_cpu_cap such as it detects being
> called on boot_cpu_data and in this case also clears bits in 'cpu_caps_cleared', thus
> while this patch does introduce a functional change, the next patch doesn't since this is the only
> place where clear_cpu_cap is called explicitly on 'boot_cpu_data'
This is not needed - this patch doing setup_clear_cpu_cap() should suffice.
But, there must be something you're fixing with this. Which is it? Some
weird virt config?
> I do now notice that initcalls are run after smp is initialized, which
> means that this code doesn't really disable the CPUID feature on all
> CPUs at all.
Well, not exactly. There's do_pre_smp_calls() which is where the
early_initcall() thing is run.
So setup_clear_cpu_cap() will make sure that the feature bit is cleared
when the APs come online.
Do you have a virt configuration where you can test this case where the
feature flag is clear on all CPUs when it fails?
I.e., "arch_lbr" will disappear in /proc/cpuinfo completely.
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2022-09-26 14:48 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-18 14:11 [PATCH v2 0/5] x86: cpuid: improve support for broken CPUID configurations Maxim Levitsky
2022-07-18 14:11 ` [PATCH v2 1/5] perf/x86/intel/lbr: use setup_clear_cpu_cap instead of clear_cpu_cap Maxim Levitsky
2022-09-19 14:31 ` Borislav Petkov
2022-09-20 8:20 ` Maxim Levitsky
2022-09-26 13:12 ` Borislav Petkov [this message]
2022-09-28 10:49 ` Maxim Levitsky
2022-10-20 8:59 ` Borislav Petkov
2022-10-20 9:05 ` Herbert Xu
2022-10-20 10:21 ` Maxim Levitsky
2022-10-20 11:13 ` Borislav Petkov
2022-10-22 21:08 ` H. Peter Anvin
2022-11-02 13:40 ` Paolo Bonzini
2022-11-02 14:27 ` Elliott, Robert (Servers)
2022-11-02 16:23 ` H. Peter Anvin
2022-11-02 18:19 ` H. Peter Anvin
2022-11-02 19:14 ` Elliott, Robert (Servers)
2022-11-03 13:26 ` Paolo Bonzini
2022-11-03 13:30 ` Paolo Bonzini
2022-07-18 14:11 ` [PATCH v2 2/5] x86/cpuid: refactor setup_clear_cpu_cap()/clear_cpu_cap() Maxim Levitsky
2022-10-21 16:19 ` Borislav Petkov
2022-11-07 19:10 ` Borislav Petkov
2022-11-07 21:57 ` Borislav Petkov
2022-07-18 14:11 ` [PATCH v2 3/5] x86/cpuid: move filter_cpuid_features to cpuid-deps.c Maxim Levitsky
2022-07-18 14:11 ` [PATCH v2 4/5] x86/cpuid: remove 'warn' parameter from filter_cpuid_features Maxim Levitsky
2022-07-18 14:11 ` [PATCH v2 5/5] x86/cpuid: check for dependencies violations in CPUID and attempt to fix them Maxim Levitsky
2022-07-28 7:30 ` [PATCH v2 0/5] x86: cpuid: improve support for broken CPUID configurations Maxim Levitsky
2022-08-01 16:05 ` Maxim Levitsky
2022-08-01 16:31 ` Dave Hansen
2022-08-01 16:41 ` Maxim Levitsky
2022-09-19 13:43 ` Maxim Levitsky
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