linux-kernel - Re: [PATCH 05/17] asm-generic/tlb: Rename HAVE_RCU_TABLE_NO

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Date:   Mon, 16 Dec 2019 16:30:47 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Piggin <npiggin@...il.com>, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>,
        Helge Deller <deller@....de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Paul Burton <paulburton@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Richard Henderson <rth@...ddle.net>,
        Nick Hu <nickhu@...estech.com>,
        Paul Walmsley <paul.walmsley@...ive.com>
Subject: Re: [PATCH 05/17] asm-generic/tlb: Rename
 HAVE_RCU_TABLE_NO_INVALIDATE

On Mon, Dec 16, 2019 at 04:14:19PM +0100, Peter Zijlstra wrote:
> On Mon, Dec 16, 2019 at 03:50:41PM +0100, Peter Zijlstra wrote:
> > On Mon, Dec 16, 2019 at 07:24:24PM +0530, Aneesh Kumar K.V wrote:
> > 
> > > So __p*_free_tlb() routines on ppc64 just mark that we need a page walk
> > > cache flush and the actual flush in done in tlb_flush_mmu.
> > 
> > Not quite, your __p*_free_tlb() goes to pgtable_free_tlb() which call
> > tlb_remove_table().
> > 
> > > As per
> > > 
> > > d86564a2f085b79ec046a5cba90188e61235280 (mm/tlb, x86/mm: Support
> > > invalidating TLB caches for RCU_TABLE_FREE ) that is not sufficient?
> > 
> > 96bc9567cbe1 ("asm-generic/tlb, arch: Invert CONFIG_HAVE_RCU_TABLE_INVALIDATE")
> > 
> > And no. Since you have TABLE_NO_INVALIDATE set, tlb_remove_table() will
> > not TLBI when it fails to allocate a batch page, which is an error for
> > PPC-Radix.
> > 
> > There is also no TLBI when the batch page is full and the RCU callback
> > happens, which is also a bug on PPC-Radix.
> 
> It seems to me you need something like this here patch, all you need to
> add is a suitable definition of tlb_needs_table_invalidate() for Power.

I'm thinking this:

#define tlb_needs_table_invalidate()	radix_enabled()

should work for you. When you have Radix you need that TLBI, if you have
Hash you don't.