linux-kernel - Re: [patch 53/60] x86/mm: Use/Fix PCID to optimize user/kernel switches

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Date:   Tue, 5 Dec 2017 14:08:59 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Borislav Petkov <bpetkov@...e.de>,
        Greg KH <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Rik van Riel <riel@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        David Laight <David.Laight@...lab.com>,
        Eduardo Valentin <eduval@...zon.com>, aliguori@...zon.com,
        Will Deacon <will.deacon@....com>,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>
Subject: Re: [patch 53/60] x86/mm: Use/Fix PCID to optimize user/kernel
 switches

On 12/05/2017 02:05 PM, Peter Zijlstra wrote:
>> I haven't checked that hard which patch introduces this bug, but it
>> seems that, with this applied, nothing propagates
>> non-mm-switch-related flushes to usermode.  Shouldn't
>> flush_tlb_func_common() contain a call to invalidate_user_asid() near
>> the bottom?  Alternatively, it could be in local_flush_tlb() and
>> __flush_tlb_single() (or whatever the hell the flush-one-usermode-TLB
>> function ends up being called).
> __native_flush_tlb_single() has the invalidate_user_asid()
> __native_flush_tlb() has the invalidate_user_asid().
> 
> Which should be exactly that last option you mention.

I can also see INVPCIDs in profiles, so it's definitely getting used.