Received-SPF: Pass (protection.outlook.com: domain of nvidia.com designates
 12.22.5.234 as permitted sender) receiver=protection.outlook.com;
 client-ip=12.22.5.234; helo=mail.nvidia.com;
From:   Alistair Popple <apopple@nvidia.com>
To:     <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
        Peter Xu <peterx@redhat.com>
CC:     Axel Rasmussen <axelrasmussen@google.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        Hugh Dickins <hughd@google.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
        Jerome Glisse <jglisse@redhat.com>,
        "Matthew Wilcox" <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>, <peterx@redhat.com>,
        David Hildenbrand <david@redhat.com>,
        Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH v6 03/23] mm: Check against orig_pte for finish_fault()
Date:   Thu, 16 Dec 2021 16:01:47 +1100
Message-ID: <6260997.DYpkEd5BTb@nvdebian>
In-Reply-To: <20211115075522.73795-4-peterx@redhat.com>
References: <20211115075522.73795-1-peterx@redhat.com> <20211115075522.73795-4-peterx@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 7Bit
Content-Type: text/plain; charset="us-ascii"
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 16 Dec 2021 05:01:55.9597
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: 2d04085f-5d24-4990-6907-08d9c0512ede
X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[12.22.5.234];Helo=[mail.nvidia.com]
X-MS-Exchange-CrossTenant-AuthSource: DM6NAM11FT032.eop-nam11.prod.protection.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Anonymous
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY4PR12MB1943
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Monday, 15 November 2021 6:55:02 PM AEDT Peter Xu wrote:
> We used to check against none pte and in those cases orig_pte should always be
> none pte anyway.

Is that always true? From what I can see in handle_pte_fault() orig_pte only
gets initialised in the !pmd_none() case so might not be pte_none.

> This change prepares us to be able to call do_fault() on !none ptes.  For
> example, we should allow that to happen for pte marker so that we can restore
> information out of the pte markers.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  mm/memory.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index 04662b010005..d5966d9e24c3 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4052,7 +4052,7 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
>  				      vmf->address, &vmf->ptl);
>  	ret = 0;
>  	/* Re-check under ptl */
> -	if (likely(pte_none(*vmf->pte)))
> +	if (likely(pte_same(*vmf->pte, vmf->orig_pte)))
>  		do_set_pte(vmf, page, vmf->address);
>  	else
>  		ret = VM_FAULT_NOPAGE;
>