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McKenney" Subject: Re: [PATCH v5 bpf-next 2/3] mm/bpf: Add bpf_get_kmem_cache() kfunc Message-ID: References: <20241010232505.1339892-1-namhyung@kernel.org> <20241010232505.1339892-3-namhyung@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Stat-Signature: bxwkbtmtexjer3gzj3qmk9cggmgtgary X-Rspamd-Queue-Id: 873A2A0016 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1728929588-23733 X-HE-Meta: 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 oWw3MUbG LuvHgnXn5M+bY7Zo3QgjwABoV9GaYVcq5bJSujHlXnV4qdn1CEQPOeujPkDB/iEsaQrpTui1svShA2ZBC0j7+JQ8K8qiBwgmKGnZzqKM6CRKcbLMc12DJEZAEckry32I9KORrsT7ZbFvaMadg/XVCRBKWw5HCqHTrStV1YQF1qGGkGEsh2QCss2A1alFXuy3vkvVK2pZaEYvJJ2u8R/H21kuVvPrboZlxmHtZebh3NAsoJfPfdmbKrpqhsq0QP++8YE4WIoNtXzfZvH/NrSDoyVjW6pFQT6GTpvjH2fmltQIN+Xl+9WrrGqLLBYSlesYvvdCMSviK/SvmyQTH00i6Zie73y8HbhaN+CFkngHXCYxJYXGG0pJ6YIinsXEF9O8GPr0tf08Rb35sZVNdb0fphMl15rrr1gCf8JEE 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: Hi Alexei, On Fri, Oct 11, 2024 at 12:14:14PM -0700, Namhyung Kim wrote: > On Fri, Oct 11, 2024 at 11:35:27AM -0700, Alexei Starovoitov wrote: > > On Thu, Oct 10, 2024 at 4:25 PM Namhyung Kim wrote: > > > > > > The bpf_get_kmem_cache() is to get a slab cache information from a > > > virtual address like virt_to_cache(). If the address is a pointer > > > to a slab object, it'd return a valid kmem_cache pointer, otherwise > > > NULL is returned. > > > > > > It doesn't grab a reference count of the kmem_cache so the caller is > > > responsible to manage the access. The returned point is marked as > > > PTR_UNTRUSTED. And the kfunc has KF_RCU_PROTECTED as the slab object > > > might be protected by RCU. > > > > ... > > > +BTF_ID_FLAGS(func, bpf_get_kmem_cache, KF_RCU_PROTECTED) > > > > This flag is unnecessary. PTR_UNTRUSTED can point to absolutely any memory. > > In this case it likely points to a valid kmem_cache, but > > the verifier will guard all accesses with probe_read anyway. > > > > I can remove this flag while applying. > > Ok, I'd be happy if you would remove it. You will need to update the bpf_rcu_read_lock/unlock() in the test code (patch 3). I can send v6 with that and Vlastimil's Ack if you want. Thanks, Namhyung