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Subject[PATCH] x86/speculation: Simplify the CPU bug detection logic
Only CPUs which speculate can speculate. Therefore, it seems prudent
to test for cpu_no_speculation first and only then determine whether
a specific speculating CPU is susceptible to store bypass speculation.
This is underlined by all CPUs currently listed in cpu_no_speculation
were present in cpu_no_spec_store_bypass as well.

Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
---
arch/x86/kernel/cpu/common.c | 18 +++++-------------
1 file changed, 5 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 78decc3e3067..2fcc1fbf11b0 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -942,12 +942,8 @@ static const __initconst struct x86_cpu_id cpu_no_meltdown[] = {
{}
};

+/* Only list CPUs which speculate but are non susceptible to SSB */
static const __initconst struct x86_cpu_id cpu_no_spec_store_bypass[] = {
- { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_PINEVIEW },
- { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_LINCROFT },
- { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_PENWELL },
- { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_CLOVERVIEW },
- { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_CEDARVIEW },
{ X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_SILVERMONT1 },
{ X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_AIRMONT },
{ X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_SILVERMONT2 },
@@ -955,14 +951,10 @@ static const __initconst struct x86_cpu_id cpu_no_spec_store_bypass[] = {
{ X86_VENDOR_INTEL, 6, INTEL_FAM6_CORE_YONAH },
{ X86_VENDOR_INTEL, 6, INTEL_FAM6_XEON_PHI_KNL },
{ X86_VENDOR_INTEL, 6, INTEL_FAM6_XEON_PHI_KNM },
- { X86_VENDOR_CENTAUR, 5, },
- { X86_VENDOR_INTEL, 5, },
- { X86_VENDOR_NSC, 5, },
{ X86_VENDOR_AMD, 0x12, },
{ X86_VENDOR_AMD, 0x11, },
{ X86_VENDOR_AMD, 0x10, },
{ X86_VENDOR_AMD, 0xf, },
- { X86_VENDOR_ANY, 4, },
{}
};

@@ -973,16 +965,16 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
if (cpu_has(c, X86_FEATURE_ARCH_CAPABILITIES))
rdmsrl(MSR_IA32_ARCH_CAPABILITIES, ia32_cap);

- if (!x86_match_cpu(cpu_no_spec_store_bypass) &&
- !(ia32_cap & ARCH_CAP_SSB_NO))
- setup_force_cpu_bug(X86_BUG_SPEC_STORE_BYPASS);
-
if (x86_match_cpu(cpu_no_speculation))
return;

setup_force_cpu_bug(X86_BUG_SPECTRE_V1);
setup_force_cpu_bug(X86_BUG_SPECTRE_V2);

+ if (!x86_match_cpu(cpu_no_spec_store_bypass) &&
+ !(ia32_cap & ARCH_CAP_SSB_NO))
+ setup_force_cpu_bug(X86_BUG_SPEC_STORE_BYPASS);
+
if (x86_match_cpu(cpu_no_meltdown))
return;

--
2.17.0
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