During early boot, spectre_v2_check_boottime_disable() sets the RETPOLINE_AMD feature for AMD hardware (before init_amd() is called). Since the RETPOLINE_AMD feature uses LFENCE to perform speculation control, it can only be used if LFENCE is serializing. Clear the RETPOLINE_AMD feature if the MSR write to make LFENCE serializing is not successful.
Signed-off-by: Tom Lendacky <[email protected]> --- arch/x86/kernel/cpu/amd.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index ea831c8..8a0076b 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -13,6 +13,7 @@ #include <asm/smp.h> #include <asm/pci-direct.h> #include <asm/delay.h> +#include <asm/nospec-branch.h> #ifdef CONFIG_X86_64 # include <asm/mmconfig.h> @@ -854,6 +855,9 @@ static void init_amd(struct cpuinfo_x86 *c) } else { /* MFENCE stops RDTSC speculation */ set_cpu_cap(c, X86_FEATURE_MFENCE_RDTSC); + + /* Don't use the LFENCE-based retpoline support */ + retpoline_amd_disable(); } }
