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bh=CORAwJdGdFJqSXpfBY2eBhV3jtyb7N9hwR1HOp2miIw=; b=mlgQCiQuOrsco+po4sSITtC11nph9KQwzE+DSpGJF+GzYbY1iOkm+3JPijRAA5OPBTYb6Q cVSO8otipo4wfZTMR9e4XBBy7+JZWjVU78K6a6RbI0La0EjxVpHCOfajgXBYkW9pF5mIXq MlOfJJTps1zAjYHYoUraLaIKshDoNKjvRocZeBCwdTQVYw4qZfIwfNdNvPStyBPsBA4mLl 34iqpxCz3hMPEH8Q1L2pQRcmKyoMQeBTVMkaLkZkmiM8/40W3mmcqN7vd10cylBbYoZ9bg uMqnQytDLVcIlT2rUK9A5IB9f59wnGpgcz8y0nYaOE2A3fDlx9Xnjr1IpgLgmw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1743752015; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=CORAwJdGdFJqSXpfBY2eBhV3jtyb7N9hwR1HOp2miIw=; b=f4D9D1uBxpPnWMpsC1nrSzp/rcZLMY6vogYgkx7/pYNMe8b3tUWHHdgp5rXAqD/prNL9o3 0oyADrspMYRwtfBQ== To: Jocelyn Falempe , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Ryosuke Yasuoka , Javier Martinez Canillas , Wei Yang , Andrew Morton , David Hildenbrand , John Ogness , linux-mm@kvack.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Cc: Jocelyn Falempe , Simona Vetter Subject: Re: [PATCH v2 1/2] mm/kmap: Add kmap_local_page_try_from_panic() In-Reply-To: <20250321112436.1739876-2-jfalempe@redhat.com> References: <20250321112436.1739876-1-jfalempe@redhat.com> <20250321112436.1739876-2-jfalempe@redhat.com> Date: Fri, 04 Apr 2025 09:33:35 +0200 Message-ID: <87mscwv0s0.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Queue-Id: 4006240007 X-Rspamd-Server: rspam05 X-Rspam-User: X-Stat-Signature: 1rxn788dd7fxkawuohq4o78kxrjcnzfm X-HE-Tag: 1743752018-172587 X-HE-Meta: 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 lOZSv6BG d6TUJA5TfbQlmUoG0nwqTaDJ9vK3whm3VBzupHY+9t2XyMhZx4xzA8tZC2CIBakjWkYqn+qm6e0XpuPJS7lQg7GWr6Iq9M2WcEmDgdkZvVIKjSxdPeS3OjtsNSGv7OKwtTxoZOYv6rLlJujEIcj+DdgNmXVGQjuKuqnnTAi1ZGKVe+g5ncaI2yHeGLzgp61UgG96kZ9Dnl0pDsZFTHkRy26GlXdmdi00gwUEboN4tEp6YsRqBSt78MZdvaO0pjkkpEmb99KCySdID/Wjs43iwm52enU6XTLqX+sGFshioEYMTRnqyEoKiDzG9W/HsKUytY6uOmsFf81dePew= 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: List-Subscribe: List-Unsubscribe: On Fri, Mar 21 2025 at 12:16, Jocelyn Falempe wrote: > kmap_local_page() can be unsafe to call from a panic handler, if > CONFIG_HIGHMEM is set, and the page is in the highmem zone. > So add kmap_local_page_try_from_panic() to handle this case. I think this is a reasonable solution and the highmem case can suffer from not getting the reliable panic output. > Suggested-by: Simona Vetter > Signed-off-by: Jocelyn Falempe > --- > include/linux/highmem-internal.h | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/include/linux/highmem-internal.h b/include/linux/highmem-internal.h > index dd100e849f5e0..5d089b0ca56de 100644 > --- a/include/linux/highmem-internal.h > +++ b/include/linux/highmem-internal.h > @@ -73,6 +73,13 @@ static inline void *kmap_local_page(struct page *page) > return __kmap_local_page_prot(page, kmap_prot); > } > > +static inline void *kmap_local_page_try_from_panic(struct page *page) > +{ > + if (!PageHighMem(page)) > + return page_address(page); > + return NULL; A comment explaining the reason why the highmem mapping cannot work here would be appreciated. Aside of that: Reviewed-by: Thomas Gleixner Thanks, tglx