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

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Message-ID: <20180823233142.GB4487@brain-police>
Date:   Fri, 24 Aug 2018 00:31:43 +0100
From:   Will Deacon <will.deacon@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     torvalds@...ux-foundation.org, luto@...nel.org, x86@...nel.org,
        bp@...en8.de, riel@...riel.com, jannh@...gle.com,
        ascannell@...gle.com, dave.hansen@...el.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Nicholas Piggin <npiggin@...il.com>,
        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 Wed, Aug 22, 2018 at 05:55:27PM +0200, Peter Zijlstra wrote:
> On Wed, Aug 22, 2018 at 05:30:15PM +0200, Peter Zijlstra wrote:
> > ARM
> > which later used this put an explicit TLB invalidate in their
> > __p*_free_tlb() functions, and PowerPC-radix followed that example.
> 
> > +/*
> > + * If we want tlb_remove_table() to imply TLB invalidates.
> > + */
> > +static inline void tlb_table_invalidate(struct mmu_gather *tlb)
> > +{
> > +#ifdef CONFIG_HAVE_RCU_TABLE_INVALIDATE
> > +	/*
> > +	 * Invalidate page-table caches used by hardware walkers. Then we still
> > +	 * need to RCU-sched wait while freeing the pages because software
> > +	 * walkers can still be in-flight.
> > +	 */
> > +	__tlb_flush_mmu_tlbonly(tlb);
> > +#endif
> > +}
> 
> 
> Nick, Will is already looking at using this to remove the synchronous
> invalidation from __p*_free_tlb() for ARM, could you have a look to see
> if PowerPC-radix could benefit from that too?
> 
> Basically, using a patch like the below, would give your tlb_flush()
> information on if tables were removed or not.

Just to say that I have something up and running for arm64 based on this.
I'll post it once it's seen a bit more testing (either tomorrow or Monday).

Will