Messages in this thread | | | Date | Tue, 23 Jan 2018 10:12:01 -0800 | From | Andi Kleen <> | Subject | Re: [PATCH v2 5/5] x86/pti: Do not enable PTI on fixed Intel processors |
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> > - if (c->x86_vendor != X86_VENDOR_AMD) > - setup_force_cpu_bug(X86_BUG_CPU_MELTDOWN); > + if (c->x86_vendor != X86_VENDOR_AMD) { > + u64 ia32_cap = 0; > + > + if (cpu_has(c, X86_FEATURE_ARCH_CAPABILITIES)) > + rdmsrl(MSR_IA32_ARCH_CAPABILITIES, ia32_cap); > + if (!(ia32_cap & ARCH_CAP_RDCL_NO)) > + setup_force_cpu_bug(X86_BUG_CPU_MELTDOWN);
This means that in a hypervisor which passes through the CPUID, but actually doesn't implement the MSR (so rdmsr #GPs and returns 0) it would be cleared.
It would be better to usr rdmsrl_safe and check the return value.
-Andi
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