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b=RqzM5BplaihQXibm6nlVaBDDzmIOWIvxhK0wlXszfxFg5Pw05CvTodjLQN6z6pRYz nANf/DnX2Ocy7PIgOh414gzXsvylzZC5lJzDH0iVw3/Vi41Ajzl6SCsvarMlcpcwSd 3NICzOyF4HLY9QslihWNlh7qbuC9kPbsIts0K/k7zWM+lTGhX5AgwzCTIfAgJfoqA7 YYPSfO0UTHNJq2yOXCVPYU+h0/UXpHqkQQ0BXofd3PqVTzHN42SMUYV/ii0XxfKlsB YQlhb+i+f07L7K36MV7c1/GePQiYPFKssXHt/NpvHdqF7S12CNTIOUTcjcZvtO7oFd 53gsmbbEeEl2g== Date: Fri, 24 Apr 2026 12:25:21 -0400 From: Sasha Levin To: "Vlastimil Babka (SUSE)" Cc: akpm@linux-foundation.org, david@kernel.org, corbet@lwn.net, ljs@kernel.org, Liam.Howlett@oracle.com, rppt@kernel.org, surenb@google.com, mhocko@suse.com, skhan@linuxfoundation.org, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC 0/7] mm: dual-bitmap page allocator consistency checker Message-ID: References: <20260424140056.2094777-1-sashal@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: X-Stat-Signature: j36i5ecyh4g6kjitgbcbbspn9sib9ugm X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 6AC4118000F X-HE-Tag: 1777047924-171200 X-HE-Meta: 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 fuaDhFCu hjdIHiVl5My3Gr1JlKIzPcPaozzm0BS13c8aRj9SxqMKTV1wD1iFqxwf433f7tiUjsOfkmNlIpJNn42FSGoEF/7rXl2lKPwzW3XRp7mZJGlQc9ka2rSGTpeD+rL5VLrqW64a1IIc1u6DQOLsonA66A7Ol7ZoFXku+YBup0qJUQtfynAWHlzsgmg4+kTv3HF9FXail9PJWp/EIwtMJwyhTg193H6DAsYkj5FmHpjJiaOHtTlrC/Qwcl5dZm+pJ2e8xo+oc Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Apr 24, 2026 at 05:42:53PM +0200, Vlastimil Babka (SUSE) wrote: >On 4/24/26 16:00, Sasha Levin wrote: >> Existing memory debugging tools - KASAN, KFENCE, page_poisoning - detect >> access violations and content corruption, but none of them can detect >> silent corruption in the page allocator's own metadata. If a hardware >> bit flip corrupts an allocation bitmap, the allocator hands out a page > >An allocation what? The page allocator is a buddy allocator, it has no >bitmap to track free/allocated state of pages? You're right, the cover letter is misleading there. Buddy doesn't use a bitmap: PageBuddy lives in page_type, the free list is a list, and page->private holds the order. The dual-bitmap is new metadata the feature adds, maintained from the alloc/free hooks. What it actually catches is the same PFN being handed out twice before it's freed, or freed without having been allocated. Not every kind of buddy corruption shows up that way, but the common bad ones do. Corruption of the bitmap itself shows up through the complement invariant. I'll fix the wording in v2. -- Thanks, Sasha