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Date: Fri, 24 Aug 2018 15:14:40 +0200
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 3/4] mm/tlb, x86/mm: Support invalidating TLB caches for
 RCU_TABLE_FREE
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To: Benjamin Herrenschmidt <benh@au1.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, Nick Piggin <npiggin@gmail.com>, Andrew Lutomirski <luto@kernel.org>, the arch/x86 maintainers <x86@kernel.org>, Borislav Petkov <bp@alien8.de>, Will Deacon <will.deacon@arm.com>, Rik van Riel <riel@surriel.com>, Jann Horn <jannh@google.com>, Adin Scannell <ascannell@google.com>, Dave Hansen <dave.hansen@intel.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>, David Miller <davem@davemloft.net>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Michael Ellerman <mpe@ellerman.id.au>

On Fri, Aug 24, 2018 at 03:13:32PM +0200, Peter Zijlstra wrote:
> + *  HAVE_RCU_TABLE_FREE
> + *
> + *  This provides tlb_remove_table(), to be used instead of tlb_remove_page()
> + *  for page directores (__p*_free_tlb()). This provides separate freeing of
> + *  the page-table pages themselves in a semi-RCU fashion (see comment below).
> + *  Useful if your architecture doesn't use IPIs for remote TLB invalidates
> + *  and therefore doesn't naturally serialize with software page-table walkers.
> + *
> + *  HAVE_RCU_TABLE_INVALIDATE
> + *
> + *  This makes HAVE_RCU_TABLE_FREE call tlb_flush_mmu_tlbonly() before freeing
> + *  the page-table pages. Required if you use HAVE_RCU_TABLE_FREE and your
> + *  architecture uses the Linux page-tables natively.

Writing that also made me think we maybe should've negated that option.