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a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1681775303; bh=5Zdo30UwbY/ugu5/xvKsTrl3c9ZrDjjdWYxF5rzZT84=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=sVSf3VXBkTRXrirTwU3FG2FBV7kU4yfoxfiWm7KupFJBq0aLURnd6HUp/GZlsbc+3 AFA6HPhkZkm7DvYCkWOct6xO3S1WXD0jZ00eeJ32RV6LKYYYy5sHDNLNFe3wk4yRuR NXNS1wOJHqds6ummn+iJkFYaHoKPuy7smosu3Bic= Date: Mon, 17 Apr 2023 16:48:22 -0700 From: Andrew Morton To: Peter Xu Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mike Kravetz , Andrea Arcangeli , Mika =?ISO-8859-1?Q?Penttil=E4?= , Axel Rasmussen , Nadav Amit , David Hildenbrand , linux-stable Subject: Re: [PATCH v2 2/6] mm/hugetlb: Fix uffd-wp bit lost when unsharing happens Message-Id: <20230417164822.d1f5d162115c53aab4c85e85@linux-foundation.org> In-Reply-To: <20230417195317.898696-3-peterx@redhat.com> References: <20230417195317.898696-1-peterx@redhat.com> <20230417195317.898696-3-peterx@redhat.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: D822C4000E X-Rspamd-Server: rspam01 X-Stat-Signature: dzb7c6u75f46apcc3x6jstkc9x4ozngb X-HE-Tag: 1681775304-444940 X-HE-Meta: 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 WRMV/Y5I XiUQaELe4bVYT8w7cJartASq+EFJGAShmUJVT3AUJ1A9WHJyiLfU8VS6YLinsRAW1bixlZBK11xnZWxXOlcVsDjpkAG4/XL1hk2gbSxDbL/vzlu+REWCYe38XJJZU+AFGG2bmebV2u2SFwdVdz9Ix09qd3LnVW5IXQySua6cAWhlIYl/2ATia1T6aPfkPGnN3jMEhczaRykUJ7Th6deTkAS4wH7gsjawLlB7INmVVYvjycmaEOVF+oICUqF3jx4onfto6wFmWvGqcpXbaGau/uAuBygyVnHiPBSyZcd9ZOnLgX+0PBPBw5uL4oupHesvr4+NZ/GDZ0lbT7hCQnYYOa1ub4FwOBOTFU5JnJdMtPiJjNqWnZFWRZ13veWzQBUydKgbBUKqEO320z8CWzRJPJr7KbU3T+ZM7a0m/3YuS5PnPTcnsMU0szsAQUiZWV0UqqPc/0zoT7MnTfnuhDDPZ6s0kZYB1AzC1Qv2Oy7M25QmT061n0r9qvgm8NA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, 17 Apr 2023 15:53:13 -0400 Peter Xu wrote: > When we try to unshare a pinned page for a private hugetlb, uffd-wp bit can > get lost during unsharing. Fix it by carrying it over. > > This should be very rare, only if an unsharing happened on a private > hugetlb page with uffd-wp protected (e.g. in a child which shares the same > page with parent with UFFD_FEATURE_EVENT_FORK enabled). What are the user-visible consequences of the bug? > Cc: linux-stable When proposing a backport, it's better to present the patch as a standalone thing, against current -linus. I'll then queue it in mm-hotfixes and shall send it upstream during this -rc cycle. As presented, this patch won't go upstream until after 6.3 is released, and as it comes later in time, more backporting effort might be needed. I can rework things if this fix is reasonably urgent (the "user-visible consequences" info is the guide). If not urgent, we can leave things as they are.