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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: B118840020 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 58wf7jid8qnm3nek3sjuw4tdq9ux4s4s X-HE-Tag: 1707866982-941439 X-HE-Meta: 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 BkiXK+7Z 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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 3:14=E2=80=AFPM Andrii Nakryiko wrote: > > > here we can then use MAX_ARENA_SZ I thought about it, but decided against it, since it will be too tempting to change it without understanding the consequences. Like... > > + if ((attr->map_extra >> 32) !=3D ((attr->map_extra + vm_range -= 1) >> 32)) > > + /* user vma must not cross 32-bit boundary */ > > + return ERR_PTR(-ERANGE); here >> 32 is relevant to size and pretty much every such shift. Hence 1ull << 32 matches all those shifts. And they have to be analyzed together. > > + apply_to_existing_page_range(&init_mm, bpf_arena_get_kern_vm_st= art(arena), > > + KERN_VM_SZ - GUARD_SZ / 2, for_eac= h_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_SZ / = 2. So no reason to ask apply_to_existing_page_range() to walk the whole KERN_VM_SZ. > > + ret =3D current->mm->get_unmapped_area(filp, addr, len * 2, 0, = flags); > > + if (IS_ERR_VALUE(ret)) > > + return 0; > > Can you leave a comment why we are swallowing errors, if this is intentio= nal? argh. good catch. it's a bug. > > + if ((ret >> 32) =3D=3D ((ret + len - 1) >> 32)) > > + return ret; > > + if (WARN_ON_ONCE(arena->user_vm_start)) > > + /* checks at map creation time should prevent this */ > > + return -EFAULT; > > + return round_up(ret, 1ull << 32); > > this is still probably MAX_ARENA_SZ, no? and here it would be wrong to do that. This line has to match the logic with 'if' few lines above. Hiding behind macro is a dangerous obfuscation.