linux-kernel - Re: [PATCH 0/3] mm/arch: Fix a few collide definition on private use of VM_FAULT

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Date:   Mon, 6 Feb 2023 02:51:18 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-arm-kernel@...ts.infradead.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH 0/3] mm/arch: Fix a few collide definition on private use
 of VM_FAULT_*

On Sun, Feb 05, 2023 at 07:54:35PM -0500, Peter Xu wrote:
> On Mon, Feb 06, 2023 at 12:10:53AM +0000, Matthew Wilcox wrote:
> > On Sun, Feb 05, 2023 at 06:17:01PM -0500, Peter Xu wrote:
> > > I noticed a few collision usage on VM_FAULT_* definition in the page fault
> > > path on arm/arm64/s390 where the VM_FAULT_* can overlap with the generic
> > > definition of vm_fault_reason.
> > > 
> > > The major overlapped part being VM_FAULT_HINDEX_MASK which is used only by
> > > the hugetlb hwpoisoning.
> > > 
> > > I'm not sure whether any of them can have a real impact, but that does not
> > > look like to be expected.  I didn't copy stable, if anyone thinks it should
> > > please shoot.  Nor did I test them in any form - I just changed the
> > > allocations from top bits and added a comment for each of them.
> > 
> > This seems like a bad way to do it.  Why not just put these VM_FAULT_*
> > definitions in linux/mm_types.h?  Then we'll see them when adding new
> > VM_FAULT codes.  Sure, they won't be used by every architecture, but
> > so what?
> 
> My initial version actually contains a few VM_FAULT_PRIVATE_N there, but I

That wasn't what I meant.  I meant putting VM_FAULT_BADMAP and
VM_FAULT_SIGSEGV in mm_types.h.  Not having "Here is a range of reserved
arch private ones".