linux-kernel - Re: [RFC PATCH 0/2] minor mmu

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Message-ID: <20180824093543.29549aa5@roar.ozlabs.ibm.com>
Date:   Fri, 24 Aug 2018 09:35:43 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andrew Lutomirski <luto@...nel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Will Deacon <will.deacon@....com>,
        Rik van Riel <riel@...riel.com>,
        Jann Horn <jannh@...gle.com>,
        Adin Scannell <ascannell@...gle.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        David Miller <davem@...emloft.net>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [RFC PATCH 0/2] minor mmu_gather patches

On Thu, 23 Aug 2018 12:15:37 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Thu, Aug 23, 2018 at 1:47 AM Nicholas Piggin <npiggin@...il.com> wrote:
> >
> > These are split from some patches I posted a while back, I was going
> > to take a look and revive the series again after your fixes go in,
> > but having another look, it may be that your "[PATCH 3/4] mm/tlb,
> > x86/mm: Support invalidating TLB caches for RCU_TABLE_FREE" becomes
> > easier after my patch 1.
> >
> > And I'm not convinced patch 2 is not a real bug at least for ARM64,
> > so it may be possible to squeeze it in if it's reviewed very
> > carefully (I need to actually reproduce and trace it).
> >
> > So not signed off by yet, but if you think it might be worth doing
> > these with your changes, it could be a slightly cleaner end result?  
> 
> Actually, you did have sign-offs, and yes, that patch 1/2 does
> actually clean up and simplify the HAVE_RCU_TABLE_INVALIDATE fix, so I
> decided to mix these in with PeterZ's series.
> 
> And since it turns out that patch doesn't apparently matter for
> correctness and doesn't need to be backported to stable, I put it at
> the end of the series together with the x86 cleanup patch to avoid the
> unnecessary RCU-delayed freeing entirely for the non-PV case.
> 
> So right now my "tlb-fixes" branch looks like this:
> 
>     x86/mm/tlb: Revert the recent lazy TLB patches
>  *  mm: move tlb_table_flush to tlb_flush_mmu_free
>  *  mm/tlb: Remove tlb_remove_table() non-concurrent condition
>  *  mm/tlb, x86/mm: Support invalidating TLB caches for RCU_TABLE_FREE
>     mm: mmu_notifier fix for tlb_end_vma
>     x86/mm: Only use tlb_remove_table() for paravirt
> 
> where the three starred patches are marked for stable.
> 
> The initial revert is for this merge window only, and the two last
> patches are cleanups and fixes but shouldn't matter for correctness in
> stable.
> 
> PeterZ - your "mm/tlb, x86/mm: Support invalidating TLB caches for
> RCU_TABLE_FREE" patch looks exactly the same, but it now no longer has
> the split of tlb_flush_mmu_tlbonly(), since with Nick's patch to move
> the call to tlb_table_flush(tlb) into tlb_flush_mmu_free, there's no
> need for the separate double-underscore version.
> 
> I hope nothing I did screwed things up. It all looks sane to me.
> Famous last words.
> 
> I'll do a few more test builds and boots, but I think I'm going to
> merge it in this cleaned-up and re-ordered form.

I think the end result looks okay, modulo my build screw up --
at least the generic code. Thanks for putting it together.

Thanks,
Nick