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From: Andy Lutomirski <luto@kernel.org>
Date: Mon, 4 Dec 2017 14:25:43 -0800
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Subject: Re: [patch 55/60] x86/mm: Use INVPCID for __native_flush_tlb_single()
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirsky <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Dave Hansen <dave.hansen@intel.com>, Borislav Petkov <bpetkov@suse.de>,
        Greg KH <gregkh@linuxfoundation.org>, Kees Cook <keescook@google.com>,
        Hugh Dickins <hughd@google.com>, Brian Gerst <brgerst@gmail.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Denys Vlasenko <dvlasenk@redhat.com>, Rik van Riel <riel@redhat.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        David Laight <David.Laight@aculab.com>,
        Eduardo Valentin <eduval@amazon.com>, aliguori@amazon.com,
        Will Deacon <will.deacon@arm.com>,
        Daniel Gruss <daniel.gruss@iaik.tugraz.at>,
        Dave Hansen <dave.hansen@linux.intel.com>
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On Mon, Dec 4, 2017 at 6:08 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> From: Dave Hansen <dave.hansen@linux.intel.com>
>
> This uses INVPCID to shoot down individual lines of the user mapping
> instead of marking the entire user map as invalid. This
> could/might/possibly be faster.
>
> This for sure needs tlb_single_page_flush_ceiling to be redetermined;
> esp. since INVPCID is _slow_.

I'm wondering if INVPCID is *so* slow that this patch is entirely
counterproductive.

--Andy