linux-kernel - Re: [PATCH] x86/cpuid: Fix up "virtual" IBRS/IBPB/STIBP feature bits on Intel

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Date:   Tue, 30 Jan 2018 11:58:14 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     David Woodhouse <dwmw@...zon.co.uk>
Cc:     arjan@...ux.intel.com, tglx@...utronix.de, karahmed@...zon.de,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        tim.c.chen@...ux.intel.com, peterz@...radead.org,
        pbonzini@...hat.com, ak@...ux.intel.com,
        torvalds@...ux-foundation.org, gregkh@...ux-foundation.org
Subject: Re: [PATCH] x86/cpuid: Fix up "virtual" IBRS/IBPB/STIBP feature bits
 on Intel

On Mon, Jan 29, 2018 at 11:49:33PM +0000, David Woodhouse wrote:
> Despite the fact that all the other code there seems to be doing it,
> just using set_cpu_cap() in early_intel_init() doesn't actually work.
> 
> When the CPU is queried again in identify_boot_cpu(), it all gets
> overwritten again. Do it in init_scattered_cpuid_features() instead.
> 
> Turning the bits off for bad microcode can use setup_clear_cpu_cap()
> to force them off for all CPUs; I was less keen on forcing the feature
> bits *on* that way.
> 
> Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
> Fixes: 2961298e ("x86/cpufeatures: Clean up Spectre v2 related CPUID flags")
> ---
> I feel I must be missing something. Is the rest of early_init_intel() broken too?

Does that help?

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 6936d14d4c77..1dd596d0a6c4 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -182,21 +182,21 @@ static void early_init_intel(struct cpuinfo_x86 *c)
 	 * Intel CPUs, for finer-grained selection of what's available.
 	 */
 	if (cpu_has(c, X86_FEATURE_SPEC_CTRL)) {
-		set_cpu_cap(c, X86_FEATURE_IBRS);
-		set_cpu_cap(c, X86_FEATURE_IBPB);
+		setup_force_cpu_cap(X86_FEATURE_IBRS);
+		setup_force_cpu_cap(X86_FEATURE_IBPB);
 	}
 	if (cpu_has(c, X86_FEATURE_INTEL_STIBP))
-		set_cpu_cap(c, X86_FEATURE_STIBP);
+		setup_force_cpu_cap(X86_FEATURE_STIBP);
 
 	/* Now if any of them are set, check the blacklist and clear the lot */
 	if ((cpu_has(c, X86_FEATURE_IBRS) || cpu_has(c, X86_FEATURE_IBPB) ||
 	     cpu_has(c, X86_FEATURE_STIBP)) && bad_spectre_microcode(c)) {
 		pr_warn("Intel Spectre v2 broken microcode detected; disabling Speculation Control\n");
-		clear_cpu_cap(c, X86_FEATURE_IBRS);
-		clear_cpu_cap(c, X86_FEATURE_IBPB);
-		clear_cpu_cap(c, X86_FEATURE_STIBP);
-		clear_cpu_cap(c, X86_FEATURE_SPEC_CTRL);
-		clear_cpu_cap(c, X86_FEATURE_INTEL_STIBP);
+		setup_clear_cpu_cap(X86_FEATURE_IBRS);
+		setup_clear_cpu_cap(X86_FEATURE_IBPB);
+		setup_clear_cpu_cap(X86_FEATURE_STIBP);
+		setup_clear_cpu_cap(X86_FEATURE_SPEC_CTRL);
+		setup_clear_cpu_cap(X86_FEATURE_INTEL_STIBP);
 	}
 
 	/*

-- 
Regards/Gruss,
    Boris.

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