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Tue, 19 Aug 2025 01:44:11 -0700 (PDT) Message-ID: <17e83e3c-1314-4198-82eb-ffc18454e344@gmail.com> Date: Tue, 19 Aug 2025 12:44:09 +0400 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] arm64/mm: Update create_kpti_ng_temp_pgd() to handle pgtable_alloc failure To: David Hildenbrand , Chaitanya S Prakash , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Ryan Roberts , Yang Shi , Catalin Marinas , Will Deacon , Kevin Brodsky , Anshuman Khandual , Andrew Morton , Zhenhua Huang , Joey Gouly References: <20250813145607.1612234-1-chaitanyas.prakash@arm.com> <20250813145607.1612234-3-chaitanyas.prakash@arm.com> <4289fc02-8e09-4d33-a4a1-0e4b268b008c@redhat.com> Content-Language: en-US From: Giorgi Tchankvetadze In-Reply-To: <4289fc02-8e09-4d33-a4a1-0e4b268b008c@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 9F573180004 X-Stat-Signature: corojphcpz78uzhf7zwem5dyjdy9eurr X-Rspam-User: X-HE-Tag: 1755593053-830379 X-HE-Meta: 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 ryAWG0mn hXRgGx4H0k6s4sQG7fRKBDb30w9pRNiSPGRvFZQJ6c76VsRPAjLMS5MEjVMT6kp2rCo2etJHF1+0CjKwdiFKTCJD7aJ7Te9V41n9N6hIY78MtO2U= 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: Smart! BUG_ON() ends up in the generic “kernel bug” path, which on many distros is configured to continue after printing the back-trace (e.g. panic_on_oops=0). Since a memory-allocation failure in early boot is unrecoverable , we must force a halt. On 8/19/2025 11:41 AM, David Hildenbrand wrote: > On 13.08.25 16:56, Chaitanya S Prakash wrote: >> create_kpti_ng_temp_pgd() was created as an alias for void returning >> __create_pgd_mapping_locked() and relied on pgtable_alloc() to BUG_ON() >> if an allocation failure occurred. But as __create_pgd_mapping_locked() >> has been updated as a part of the error propagation patch to return a >> non-void value, update create_kpti_ng_temp_pgd() to act as a wrapper >> around __create_pgd_mapping_locked() and BUG_ON() on ret being a non >> zero value. > > If  my memory serves me right, panic() is preferred in such unexpected > early-boot scenarios (BUG_ON is frowned upon), where you can actually > print what is going wrong.