linux-kernel - Re: [RFC][PATCH 1/5] mm: Rework {set,clear,mm}_tlb_flush

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Date:   Wed, 02 Aug 2017 23:57:04 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Will Deacon <will.deacon@....com>, torvalds@...ux-foundation.org,
        oleg@...hat.com, paulmck@...ux.vnet.ibm.com, mpe@...erman.id.au,
        npiggin@...il.com, linux-kernel@...r.kernel.org, mingo@...nel.org,
        stern@...land.harvard.edu, Mel Gorman <mgorman@...e.de>,
        Rik van Riel <riel@...hat.com>
Subject: Re: [RFC][PATCH 1/5] mm: Rework {set,clear,mm}_tlb_flush_pending()

On Wed, 2017-08-02 at 10:11 +0200, Peter Zijlstra wrote:

> which should be completely ordered against anything prior and anything
> following, and is I think the behaviour we want from TLB flushes in
> general, but is very much not provided by a number of architectures
> afaict.
> 
> Ah, found the hash-64 code, yes that's good too. The hash32 code lives
> in asm and confuses me, it has a bunch of SYNC, SYNC_601 and isync in.
> The nohash variant seems to do a isync after tlbwe, but again no clue.

Doing some archeology ? :-)

In the hash32 days ptesync didn't exist, sync had all the needed
semantics. tlbew isn't a proper invalidate per-se, but isync will flush
the shadow TLBs, but I wouldn't bother too much about these, if needed
I can go fix them.

> Now, do I go and attempt fixing all that needs fixing?
> 
> 
> x86 is good, our CR3 writes or INVLPG stuff is fully serializing.
> 
> arm is good, it does DSB ISH before and after
> 
> arm64 looks good too, although it plays silly games with the first
> barrier, but I trust that to be sufficient.
> 
> But I'll have to go dig up arch manuals for the rest, if they include
> the relevant information at all of course :/

Ben.