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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-Rspamd-Queue-Id: AE63D40003 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: rcw1mzhdwts9jq3d9a8kca7bp6b58uxq X-HE-Tag: 1728674055-994042 X-HE-Meta: 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 7l4q5oHv w8fMtG97LGqj6LQWMLoO+1riRCZKn0+tkXZRVfdqSw8U5rPwH8iAMHGxL7Ge7zBkpn4GTRMB/XexbXvFNmvTXE/eQx89/P0ujkvp8Cnc/xDOY3pREYJflyew8ihshJCHzdaDlVwCUC3OZZeml0cZel69sJ08qvTAnwUIs8XQYi674r5Edp+dqamgg58PycHdszEbY0pawzrR1t5zoxctAgRB6YKw61oq2UrNspJAeuue0Ua0bAHGnhN+k2FSVk4Nd3u0x7vTSu7D8zyvRg/0a+80lOvzgNsIi9ITQp8qRBceJKDnGIbzkcIAPgNlnOxnevQVCYID0WpJCaYRQ7ncY8BXBrInaXRLYVusx3S4qxapn45cPqcxRahkv8w1DB8zAUksMzejOZX761LjCbuq1pyedP8+JcHX8waw5 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 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. Thanks, Namhyung