On Wed, 8 Jul 2015, Peter Zijlstra wrote:
> On Wed, Jul 08, 2015 at 11:17:38AM -0400, Mikulas Patocka wrote:
> > Hi
> >
> > I found out that the patch a66734297f78707ce39d756b656bfae861d53f62 breaks
> > the kernel on processors without performance counters, such as AMD K6-3.
> > Reverting the patch fixes the problem.
> >
> > The static key rdpmc_always_available somehow gets set (I couldn't really
> > find out what is setting it, the function set_attr_rdpmc is not executed),
> > cr4_set_bits(X86_CR4_PCE) is executed and that results in a crash on boot
> > when attempting to execute init, because the proecssor doesn't support
> > that bit in CR4.
>
> Urgh, the static key trainwreck bites again.
>
> One is not supposed to mix static_key_true() and STATIC_KEY_INIT_FALSE.
>
> Does this make it go again?
Yes, this patch fixes the problem.
Mikulas
> ---
> arch/x86/include/asm/mmu_context.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/mmu_context.h
> b/arch/x86/include/asm/mmu_context.h
> index 5e8daee7c5c9..804a3a6030ca 100644
> --- a/arch/x86/include/asm/mmu_context.h
> +++ b/arch/x86/include/asm/mmu_context.h
> @@ -23,7 +23,7 @@ extern struct static_key rdpmc_always_available;
>
> static inline void load_mm_cr4(struct mm_struct *mm)
> {
> - if (static_key_true(&rdpmc_always_available) ||
> + if (static_key_false(&rdpmc_always_available) ||
> atomic_read(&mm->context.perf_rdpmc_allowed))
> cr4_set_bits(X86_CR4_PCE);
> else
>
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