linux-kernel - Re: [PATCH v10 6/7] x86/arch_prctl: Add ARCH_[GET|SET]

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Date:   Wed, 9 Nov 2016 14:21:14 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Kyle Huey <me@...ehuey.com>,
        Robert O'Callahan <robert@...llahan.org>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Shuah Khan <shuah@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Len Brown <len.brown@...el.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Dmitry Safonov <dsafonov@...tuozzo.com>,
        David Matlack <dmatlack@...gle.com>,
        linux-kernel@...r.kernel.org,
        user-mode-linux-devel@...ts.sourceforge.net,
        user-mode-linux-user@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH v10 6/7] x86/arch_prctl: Add ARCH_[GET|SET]_CPUID

On Tue, Nov 08, 2016 at 09:06:31PM +0100, Thomas Gleixner wrote:
> The upcoming ring3 mwait stuff can add its magic to tweak that MSR into
> this function.
> 
> Stick the call at the end of init_scattered_cpuid_features() for now. I
> still need to figure out a proper place for it.

So Thomas and I discussed this more on IRC and I think we can get rid
of the MSR iterating in scattered.c and integrate both the R3 MWAIT and
CPUID faulting like this:

---
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index fcd484d2bb03..5c38a85af2e7 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -452,6 +457,39 @@ static void intel_bsp_resume(struct cpuinfo_x86 *c)
 	init_intel_energy_perf(c);
 }
 
+static void init_misc_enables(struct cpuinfo_x86 *c)
+{
+	u64 val, misc_en;
+
+	if (rdmsrl_safe(MSR_MISC_FEATURES_ENABLES, &misc_en))
+		return;
+
+	misc_en &= ~MSR_MISC_ENABLES_CPUID_FAULT_ENABLE;
+
+	if (!rdmsrl_safe(MSR_PLATFORM_INFO, &val)) {
+		if (val & PLATINFO_CPUID_FAULT_BIT)
+			set_cpu_cap(c, X86_FEATURE_CPUID_FAULT);
+	}
+
+	wrmsrl(MSR_MISC_FEATURES_ENABLES, misc_en);
+	this_cpu_write(msr_misc_features_enables_shadow, misc_en);
+}
+
 static void init_intel(struct cpuinfo_x86 *c)
 {
 	unsigned int l2 = 0;
@@ -565,6 +603,8 @@ static void init_intel(struct cpuinfo_x86 *c)
 		detect_vmx_virtcap(c);
 
 	init_intel_energy_perf(c);
+
+	init_misc_enables(c);
 }
 
 #ifdef CONFIG_X86_32
---

Please redo your patchset and add the detection to init_intel() like above.

Also, let's call that MSR mask MSR_MISC_ENABLES_CPUID_FAULT_ENABLE like
the rest of the bits in msr-index.h

Thanks.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--