From: Peter Zijlstra <peterz@infradead.org>
To: Dave Hansen <dave.hansen@linux.intel.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
tglx@linutronix.de, richard.fellner@student.tugraz.at,
moritz.lipp@iaik.tugraz.at, daniel.gruss@iaik.tugraz.at,
michael.schwarz@iaik.tugraz.at, luto@kernel.org,
torvalds@linux-foundation.org, keescook@google.com,
hughd@google.com, bp@alien8.de, x86@kernel.org
Subject: Re: [PATCH] x86/mm/kaiser: Flush the correct ASID in __native_flush_tlb_single()
Date: Wed, 29 Nov 2017 16:26:31 +0100 [thread overview]
Message-ID: <20171129152631.GQ3326@worktop> (raw)
In-Reply-To: <27729551-ecd6-e4e9-d214-4ab03d8008da@linux.intel.com>
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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prev parent reply other threads:[~2017-11-29 15:26 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-28 9:55 [PATCH] x86/mm/kaiser: Flush the correct ASID in __native_flush_tlb_single() Dave Hansen
2017-11-29 14:35 ` Peter Zijlstra
2017-11-29 15:21 ` Dave Hansen
2017-11-29 15:26 ` Peter Zijlstra [this message]
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