linux-kernel - Re: [PATCH 21/23] x86, pcid, kaiser: allow flushing for future ASID switches

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Message-ID: <38b34f81-3adb-98c5-c482-0d53b9155d3b@linux.intel.com>
Date:   Wed, 1 Nov 2017 07:17:45 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        moritz.lipp@...k.tugraz.at, daniel.gruss@...k.tugraz.at,
        michael.schwarz@...k.tugraz.at,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH 21/23] x86, pcid, kaiser: allow flushing for future ASID
 switches

On 11/01/2017 01:03 AM, Andy Lutomirski wrote:
>> This ensures that any futuee context switches will do a full flush
>> of the TLB so they pick up the changes.
> I'm convuced.  What was wrong with the old code?  I guess I just don't
> see what the problem is that is solved by this patch.

Instead of flushing *now* with INVPCID, this lets us flush *later* with
CR3.  It just hijacks the code that you already have that flushes CR3
when loading a new ASID by making all ASIDs look new in the future.

We have to load CR3 anyway, so we might as well just do this flush then.