linux-kernel - Re: [PATCH 3/4] mm/tlb, x86/mm: Support invalidating TLB caches for RCU_TABLE

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Date:   Fri, 24 Aug 2018 15:14:40 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Benjamin Herrenschmidt <benh@....ibm.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Nick Piggin <npiggin@...il.com>,
        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>
Subject: Re: [PATCH 3/4] mm/tlb, x86/mm: Support invalidating TLB caches for
 RCU_TABLE_FREE

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.