[PATCH v2 5/5] x86/pti: Do not enable PTI on fixed Intel processors

David Woodhouse
2018-01-23T16:52:55Z

When they advertise the IA32_ARCH_CAPABILITIES MSR and it has the RDCL_NO
bit set, they don't need KPTI either.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
arch/x86/kernel/cpu/common.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index e5d66e9..c05d0fe 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -900,8 +900,14 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)

setup_force_cpu_cap(X86_FEATURE_ALWAYS);

- 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);
+ }

setup_force_cpu_bug(X86_BUG_SPECTRE_V1);
setup_force_cpu_bug(X86_BUG_SPECTRE_V2);
--
2.7.4