Some old Atoms, anything in family 5 or 4, and newer CPUs when they advertise the IA32_ARCH_CAPABILITIES MSR and it has the RDCL_NO bit set, are not vulnerable.
Roll the AMD exemption into the x86_match_cpu() table too. Based on suggestions from Dave Hansen and Alan Cox. Signed-off-by: David Woodhouse <d...@amazon.co.uk> --- arch/x86/kernel/cpu/common.c | 34 ++++++++++++++++++++++++++++++++-- 1 file changed, 32 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index e5d66e9..3bc8a1f 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -47,6 +47,8 @@ #include <asm/pat.h> #include <asm/microcode.h> #include <asm/microcode_intel.h> +#include <asm/intel-family.h> +#include <asm/cpu_device_id.h> #ifdef CONFIG_X86_LOCAL_APIC #include <asm/uv/uv.h> @@ -853,6 +855,35 @@ static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c) #endif } +static const __initdata struct x86_cpu_id cpu_no_meltdown[] = { + { X86_VENDOR_AMD }, + { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_CEDARVIEW, X86_FEATURE_ANY }, + { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_CLOVERVIEW, X86_FEATURE_ANY }, + { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_LINCROFT, X86_FEATURE_ANY }, + { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_PENWELL, X86_FEATURE_ANY }, + { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_PINEVIEW, X86_FEATURE_ANY }, + { X86_VENDOR_ANY, 5 }, + { X86_VENDOR_ANY, 4 }, + {} +}; + +static bool __init early_cpu_vulnerable_meltdown(struct cpuinfo_x86 *c) +{ + u64 ia32_cap = 0; + + if (x86_match_cpu(cpu_no_meltdown)) + return false; + + if (cpu_has(c, X86_FEATURE_ARCH_CAPABILITIES)) + rdmsrl(MSR_IA32_ARCH_CAPABILITIES, ia32_cap); + + /* Rogue Data Cache Load? No! */ + if (ia32_cap & ARCH_CAP_RDCL_NO) + return false; + + return true; +} + /* * Do minimum CPU detection early. * Fields really needed: vendor, cpuid_level, family, model, mask, @@ -900,9 +931,8 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c) setup_force_cpu_cap(X86_FEATURE_ALWAYS); - if (c->x86_vendor != X86_VENDOR_AMD) + if (early_cpu_vulnerable_meltdown(c)) setup_force_cpu_bug(X86_BUG_CPU_MELTDOWN); - setup_force_cpu_bug(X86_BUG_SPECTRE_V1); setup_force_cpu_bug(X86_BUG_SPECTRE_V2); -- 2.7.4