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To: Andrii Nakryiko Cc: bpf , Daniel Borkmann , Andrii Nakryiko , Kumar Kartikeya Dwivedi , Eddy Z , Tejun Heo , Barret Rhoden , Johannes Weiner , Lorenzo Stoakes , Andrew Morton , Uladzislau Rezki , Christoph Hellwig , linux-mm , Kernel Team Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 5396B40002 X-Rspam-User: X-Stat-Signature: wiiex4wpusgznkm8mbee4rd7udhc7989 X-Rspamd-Server: rspam01 X-HE-Tag: 1707869670-490137 X-HE-Meta: U2FsdGVkX18YWuv51IFpL5gOlEFsn6EpHlQwXkn/PnTB7J3VGqFj3iKHFcsm7RmGMJxc853V2dRB0mQUQmRiM0K6x4pRJjsAficj6G3Xszkk8XUR+HhhElkpRMCv3J0TeNmy+83smXbDg+MmZUxGuvqAp4NLBMWCwjklpPK2A+ZIdsH9kdyW1FSEva5PHfVxHPa00mvNgJaxFxsmMI5PH2tXkFej9Qh1+mzruqI+lZAJQhriWfk3c1Wz1UJr74GIB/djm/BhIePAFZvhVSVvpSDJvKndB2HT9ERw6N8dMYFXmg0PwmIWxUb657aV6m0dTCkkpWg1euDItHgsdY9dieqo33m3WIGgiXAIYdClJVqkHXEKt01Xq9wNkl49M43wT9RLhQxIzw1UegrLEfqeegDvjV0rCi9DotWVGK9ZMRPKvJdSGxqfIyuKj9UvTC8QDCxNCXlDDikJrmC47l0RHtVeLwL4bSyoHuq0/xI3JcUHygTtskUUJNN9Hz3DPUUW8UBEgnJJwuVDZG7D3q5vdhZsMQQ//HFStskgFXx8wIBKNDq2TgyoOrACYHDyGh2UPRORk0O61bmmogD25v3sg7OUBAeAHiBQQOaeOuJrilHy7bIkItxxUKXRFb0sdVdvuDRglsR9gNymgZ4llxxixxOqgu13rhC8YTIHybwJE/M4eLpt5QRAcPqZEY2pTbtzCRw504rco6GA42HNJvhdsxDSP3QH3yeD502aCSF3jeVprHDqfhLJvSAgzAz5RGbnWQ+PIqB7K1yH5t8kvpqXkonIoTBjzK36SlxeTtuQuZ1jgtZGVz949tixQt+Nrz9ArX1X/yJvrNuEPd1s1frqv7WW6Lx/vTCUH503r9HA10L1Yz8OCNVLC3YWYeuf8fuAis3rk5jFPet4Y61FtOyqgNzx9nN/UuVLSS4NIza6EV7DIYUHd65f+vDbyjnMPZufVlYy/tU2RclGc+Y6Yaj emBHVIwO 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 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 Tue, Feb 13, 2024 at 4:03=E2=80=AFPM Andrii Nakryiko wrote: > > > > + apply_to_existing_page_range(&init_mm, bpf_arena_get_kern_vm_start(arena), > > > > + KERN_VM_SZ - GUARD_SZ / 2, for= _each_pte, NULL); > > > > > > I'm still reading the rest (so it might become obvious), but this > > > KERN_VM_SZ - GUARD_SZ / 2 is a bit surprising. I understand that > > > kern_vm_start is shifted by GUARD_SZ/2, but is the intent here is to > > > actually go beyond maximum 4GB by GUARD_SZ/2, or the intent was to > > > unmap 4GB (MAX_ARENA_SZ)? > > > > here it's just the range for apply_to_existing_page_range() to walk. > > There are no pages mapped into the lower GUARD_SZ / 2 and upper GUARD_S= Z / 2. > > So no reason to ask apply_to_existing_page_range() to walk > > the whole KERN_VM_SZ. > > right, so I expected to see KERN_VM_SZ - GUARD_SZ, but instead we have > KERN_VM_SZ - GUARD_SZ/2 (so we'll iterate GUARD_SZ/2 too much, into > upper guard pages which are supposed to be not allocated), which is > why I'm asking. It's minor, I was probing if I'm missing something > subtle. ahh. you're correct, of course. braino.