From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v5 01/11] asm-generic/pgtable: Adds generic functions to
 monitor lockless pgtable walks
Date: Fri, 4 Oct 2019 13:24:21 +0200
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To: John Hubbard <jhubbard@nvidia.com>
Cc: Song Liu <songliubraving@fb.com>, Michal Hocko <mhocko@suse.com>, "Dmitry V. Levin" <ldv@altlinux.org>, Keith Busch <keith.busch@intel.com>, linux-mm@kvack.org, Paul Mackerras <paulus@samba.org>, Christoph Lameter <cl@linux.com>, Ira Weiny <ira.weiny@intel.com>, Dan Williams <dan.j.williams@intel.com>, Elena Reshetova <elena.reshetova@intel.com>, linux-arch@vger.kernel.org, Santosh Sivaraj <santosh@fossix.org>, Davidlohr Bueso <dave@stgolabs.net>, "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>, Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>, Mike Rapoport <rppt@linux.ibm.com>, Jason Gunthorpe <jgg@ziepe.ca>, Vlastimil Babka <vbabka@suse.cz>, Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>, Leonardo Bras <leonardo@linux.ibm.com>, Alexey Dobriyan <adobriyan@gmail.com>, Ingo Molnar <mingo@kernel.org>, Andrea Arcangeli <aarcange@redhat.com>, Ralph Campbell <rcampbell@n>
List-Id: linux-arch.vger.kernel.org

On Thu, Oct 03, 2019 at 01:40:38PM -0700, John Hubbard wrote:
> On 10/3/19 4:51 AM, Peter Zijlstra wrote:
> > On Thu, Oct 03, 2019 at 09:11:45AM +0200, Peter Zijlstra wrote:
> >> On Wed, Oct 02, 2019 at 10:33:15PM -0300, Leonardo Bras wrote:
> ...
> > 
> > I'm still really confused about this barrier. It just doesn't make
> > sense.
> > 
> > If an interrupt happens before the local_irq_disable()/save(), then it
> > will discard any and all speculation that would be in progress to handle
> > the exception.
> > 
> 
> Hi Peter,
> 
> So, would that imply that it's correct to apply approximately the following
> patch:
> 
> diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
> index 1adbb8a371c7..cf41eff37e24 100644
> --- a/Documentation/memory-barriers.txt
> +++ b/Documentation/memory-barriers.txt
> @@ -2099,9 +2099,9 @@ INTERRUPT DISABLING FUNCTIONS
>  -----------------------------
>  
>  Functions that disable interrupts (ACQUIRE equivalent) and enable interrupts
> -(RELEASE equivalent) will act as compiler barriers only.  So if memory or I/O
> -barriers are required in such a situation, they must be provided from some
> -other means.
> +(RELEASE equivalent) will act as full memory barriers. This is because, for
> +all supported CPU architectures, interrupt arrival causes all speculative
> +memory accesses to be discarded.
>  
> ?

No, you're misunderstanding. They imply nothing of the sort.