Re: [RFC][PATCH 1/5] mm: Rework {set,clear,mm}_tlb_flush_pending()

From: Benjamin Herrenschmidt
Date: Wed Aug 02 2017 - 11:40:46 EST

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 :/