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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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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.