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().
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();
