On Wed, Nov 29, 2017 at 07:21:23AM -0800, Dave Hansen wrote:
> Yes, that works. Also, as I think about it, INVLPG is a safer
> (bug-resistant) instruction to use too. INVPCID _can_ get the current
> (kernel) ASID wrong, as we saw. But INVLPG always uses the current one
> and can't be wrong about flushing the *current* ASID.
>
> I think Andy measured it to be faster than INVPCID too.
>
> So, maybe we should just remove INVPCID's use entirely.
With my patches the below invpcid_flush_one() is the only remaining user
(not counting flush_tlb_global).
I know Andy hates on INVPCID, but I could not convince myself that doing
a full user invalidate makes sense for flush_tlb_single(), then again
maybe it does, the patch is trivial after this.
> > arch/x86/include/asm/tlbflush.h | 23 +++++++----------------
> > 1 file changed, 7 insertions(+), 16 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
> > index 481d5094559e..9587722162ee 100644
> > --- a/arch/x86/include/asm/tlbflush.h
> > +++ b/arch/x86/include/asm/tlbflush.h
> > @@ -438,29 +438,20 @@ static inline void __native_flush_tlb_single(unsigned long addr)
> > {
> > u32 loaded_mm_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid);
> >
> > + asm volatile("invlpg (%0)" ::"r" (addr) : "memory");
> > +
> > + if (!kaiser_enabled)
> > + return;
> > +
> > /*
> > * Some platforms #GP if we call invpcid(type=1/2) before
> > * CR4.PCIDE=1. Just call invpcid in the case we are called
> > * early.
> > */
> > + if (!this_cpu_has(X86_FEATURE_INVPCID_SINGLE))
> > flush_user_asid(loaded_mm_asid);
> > + else
> > invpcid_flush_one(user_asid(loaded_mm_asid), addr);
> > }
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