linux-kernel - Re: [PATCH 6/6] x86/mm/kaiser: Optimize __native_flush

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Date:   Thu, 30 Nov 2017 14:13:53 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Rik van Riel <riel@...hat.com>, daniel.gruss@...k.tugraz.at,
        hughd@...gle.com, keescook@...gle.com, linux-mm@...ck.org,
        michael.schwarz@...k.tugraz.at, moritz.lipp@...k.tugraz.at,
        richard.fellner@...dent.tugraz.at
Subject: Re: [PATCH 6/6] x86/mm/kaiser: Optimize __native_flush_tlb

On Thu, Nov 30, 2017 at 01:43:19PM +0100, Peter Zijlstra wrote:
> Now the problem is that flush_tlb_kernel_range() is implemented using
> either __flush_tlb_all() or __flush_tlb_single(), and it is that last
> use that is buggered.
> 
> So at the very least we need the below to cure things, but there is
> another inconsistency; do_flush_tlb_all() is used by both
> flush_tlb_all() and flush_tlb_kernel_range() and increments NR_TLB_*,
> do_kernel_range_flush() OTOH does not increment NR_TLB_*. I'm not fixing
> that, but I'll leave a comment around or something, so we can later try
> and figure out what exact statistics we want.

Alternatively, we'd simply kill the entire invlpg path for
flush_tlb_kernel_range() and simply do __flush_tlb_all().