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To: Alexei Starovoitov 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: F352F2000E X-Rspam-User: X-Stat-Signature: s6qf1id7b5up6cbbtx5547ep4aewqbxc X-Rspamd-Server: rspam03 X-HE-Tag: 1707869010-490187 X-HE-Meta: U2FsdGVkX1+gwbCMaI5S9YC1N5yev0rgAW1XEu4shu+LT8gkmTbdeYR0SPojO2Q6BIVXnmw+nlQ6jHaGxCRtqy3aOY1ssAguamIeWsM3q4040m7xOQYuc/oek748uMOoEl8Wa1VaHbgKdCw9fx/w+AtWGHHXYJj/juo4jmV9z9DFfgWc9CuUs68+k2oxqhCqIbRWzaBPztkyIstghks5DG6t1RcD1M1p4h3riyTIllXuP1CZKaxGu43hPwvJslzfJg5b8XyVnWaiNnJBgX6xSlriEjvA29HZTG17OBUrqzM1lJd4njExqf+BMkmF4dUHG66qc00/s8ioHn8rDx7ceuJ8it/uB/ioZNfPCPnRbYnjHJ+W8jZi9DrcBRFo3D8bJs8CUCC8xWkOPoPTjh/tcy6EAhP+fcMgkEiLDCvWRSE7HeVfLlhD6vSg8mLtQfMDEtJTyMrILA8Bt9wlapJtrB3JuLAc4HNDhnhI5S1SIX91yWkc3z8m9XOt2VQdygVkJo+mcvm1t8sihJwsVFFAnmNCoTkY02EtRHwnlaiNAZUTQZpv8XhDL8JRXPTi08tBoDAxa3Q19jBwS0uk2PSxY0GvCEzPzI3fWyyiGXG+RigVCPnKap/MHmG6HM21tyrbKfaObWt4raop4S1Y1cdbBwq/ZzlgxktxHDPPipoWnjxNHW/57R5gPfqJQ2QAmz76L0WEEtCjndgBs3VCnYvyseqw4CCdIRHrfxEyVNQ+mHGQ/qTpl14QFNPUW1uhxpRC+6CcjOCoSWvyah7etGrvBvh5U61nKbSs1KEHcirMIi3tYtGygjToO+QOURfecodgUxQKowWFWA6UprTCc+Ax+n2f8muOW7GQAUoHCzI+FHne6fN9zXNdNfgniy+SBbN8jbnmH1hYO9khpnmu65FRwdK7+WcdAxqPnFnLYoNAadQsn33ZcM99DppY+7BiofskmPNaMqhAB3oSvWBnnBV D+ApV0hl 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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 3:29=E2=80=AFPM Alexei Starovoitov wrote: > > 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_= start(arena), > > > + KERN_VM_SZ - GUARD_SZ / 2, for_e= ach_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. 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. > > > > + 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 intent= ional? > > 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. ok, no big deal