On 1/9/2018 4:46 PM, Thomas Gleixner wrote:
> On Tue, 9 Jan 2018, Tom Lendacky wrote:
>> For AMD hardware, the RETPOLINE_AMD feature is dependent on LFENCE being
>> a serializing instruction. Create a function to allow RETPOLINE_AMD to
>> be cleared if it cannot be determined that LFENCE is serializing. In
>> addition, update the spectre_v2_enabled variable so that sysfs output is
>> correct.
>>
>> Signed-off-by: Tom Lendacky <thomas.lenda...@amd.com>
>> ---
>> arch/x86/include/asm/nospec-branch.h | 1 +
>> arch/x86/kernel/cpu/bugs.c | 10 ++++++++++
>> 2 files changed, 11 insertions(+)
>>
>> diff --git a/arch/x86/include/asm/nospec-branch.h
>> b/arch/x86/include/asm/nospec-branch.h
>> index 8ddf851..5785684 100644
>> --- a/arch/x86/include/asm/nospec-branch.h
>> +++ b/arch/x86/include/asm/nospec-branch.h
>> @@ -153,6 +153,7 @@
>> #endif
>>
>> void spectre_v2_check_boottime_disable(void);
>> +void retpoline_amd_disable(void);
>>
>> #endif /* __ASSEMBLY__ */
>> #endif /* __NOSPEC_BRANCH_H__ */
>> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
>> index b957f77..a4c594c 100644
>> --- a/arch/x86/kernel/cpu/bugs.c
>> +++ b/arch/x86/kernel/cpu/bugs.c
>> @@ -170,6 +170,16 @@ void __init spectre_v2_check_boottime_disable(void)
>> return;
>> }
>>
>> +void retpoline_amd_disable(void)
>> +{
>> + if (!boot_cpu_has(X86_FEATURE_RETPOLINE_AMD))
>> + return;
>> +
>> + setup_clear_cpu_cap(X86_FEATURE_RETPOLINE_AMD);
>> + spectre_v2_enabled = retp_compiler() ?
>> + SPECTRE_V2_RETPOLINE_GENERIC : SPECTRE_V2_RETPOLINE_MINIMAL;
>> +}
>
> Urgh. That's an awful hack. why not do the obvious?
My first attempt was very similar to your change below, but testing
showed that spectre_v2_check_boottime_disable() is called before the
X86_FEATURE_LFENCE_RDTSC can be set. I can look at moving where the
X86_FEATURE_LFENCE_RDTSC is set, maybe into early_init_amd() or such
if you think that would be best.
Thanks,
Tom
>
> Thanks,
>
> tglx
>
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -148,14 +148,21 @@ void __init spectre_v2_check_boottime_di
> retpoline:
> if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) {
> retpoline_amd:
> + if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD ||
> + !boot_cpu_has(X86_FEATURE_LFENCE_RDTSC)) {
> + pr_info("AMD retpoline not supported, fall back to
> generic\n");
> + goto retpoline_generic;
> + }
> +
> spectre_v2_enabled = retp_compiler() ?
> SPECTRE_V2_RETPOLINE_AMD :
> SPECTRE_V2_RETPOLINE_MINIMAL_AMD;
> setup_force_cpu_cap(X86_FEATURE_RETPOLINE_AMD);
> - } else {
> - retpoline_generic:
> - spectre_v2_enabled = retp_compiler() ?
> - SPECTRE_V2_RETPOLINE_GENERIC :
> SPECTRE_V2_RETPOLINE_MINIMAL;
> + setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
> + return;
> }
> +retpoline_generic:
> + spectre_v2_enabled = retp_compiler() ?
> + SPECTRE_V2_RETPOLINE_GENERIC : SPECTRE_V2_RETPOLINE_MINIMAL;
> setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
> return;
> #else
>
>
