On 1/9/2018 5:09 PM, Thomas Gleixner wrote:
> On Tue, 9 Jan 2018, Tom Lendacky wrote:
>> On 1/9/2018 4:46 PM, Thomas Gleixner wrote:
>>> 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.
>
> Wait, we can move the selection _AFTER_ identify_boot_cpu().
Much cleaner. Since it's just a single patch now, do you want me to
re-submit this after I test it or will you just pick this up as is?
I did notice that the patch does change the behavior associated with
the command line options, though. Not sure if that was intentional.
Thanks,
Tom
>
> Thanks,
>
> tglx
>
> 8<----------------
>
> --- a/arch/x86/include/asm/nospec-branch.h
> +++ b/arch/x86/include/asm/nospec-branch.h
> @@ -152,7 +152,5 @@
> # define THUNK_TARGET(addr) [thunk_target] "rm" (addr)
> #endif
>
> -void spectre_v2_check_boottime_disable(void);
> -
> #endif /* __ASSEMBLY__ */
> #endif /* __NOSPEC_BRANCH_H__ */
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -24,6 +24,8 @@
> #include <asm/pgtable.h>
> #include <asm/set_memory.h>
>
> +static void __init spectre_v2_check_boottime_disable(void);
> +
> void __init check_bugs(void)
> {
> identify_boot_cpu();
> @@ -33,6 +35,9 @@ void __init check_bugs(void)
> print_cpu_info(&boot_cpu_data);
> }
>
> + /* Select the proper spectre mitigation before patching alternatives */
> + spectre_v2_check_boottime_disable();
> +
> #ifdef CONFIG_X86_32
> /*
> * Check whether we are able to run this kernel safely on SMP.
> @@ -106,7 +111,7 @@ static inline bool match_option(const ch
> return len == arglen && !strncmp(arg, opt, len);
> }
>
> -void __init spectre_v2_check_boottime_disable(void)
> +static void __init spectre_v2_check_boottime_disable(void)
> {
> char arg[20];
> int ret;
> @@ -148,14 +153,21 @@ 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
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -1322,8 +1322,6 @@ void __init setup_arch(char **cmdline_p)
>
> register_refined_jiffies(CLOCK_TICK_RATE);
>
> - spectre_v2_check_boottime_disable();
> -
> #ifdef CONFIG_EFI
> if (efi_enabled(EFI_BOOT))
> efi_apply_memmap_quirks();
>
