linux-kernel - Re: [PATCH] x86/mm/kaiser: Flush the correct ASID in __native_flush_tlb

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Date:   Wed, 29 Nov 2017 16:26:31 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        tglx@...utronix.de, richard.fellner@...dent.tugraz.at,
        moritz.lipp@...k.tugraz.at, daniel.gruss@...k.tugraz.at,
        michael.schwarz@...k.tugraz.at, luto@...nel.org,
        torvalds@...ux-foundation.org, keescook@...gle.com,
        hughd@...gle.com, bp@...en8.de, x86@...nel.org
Subject: Re: [PATCH] x86/mm/kaiser: Flush the correct ASID in
 __native_flush_tlb_single()

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);
> >  }