On Tue, 29 Sep 2020 at 15:48, Andrey Konovalov <andreyk...@google.com> wrote: > On Tue, Sep 29, 2020 at 3:11 PM Marco Elver <el...@google.com> wrote: > > > > On Tue, Sep 29, 2020 at 02:42PM +0200, Andrey Konovalov wrote: > > [...] > > > > + */ > > > > + index = (addr - (unsigned long)__kfence_pool) / (PAGE_SIZE * 2) > > > > - 1; > > > > > > Why do we subtract 1 here? We do have the metadata entry reserved for > > > something? > > > > Above the declaration of __kfence_pool it says: > > > > * We allocate an even number of pages, as it simplifies > > calculations to map > > * address to metadata indices; effectively, the very first page > > serves as an > > * extended guard page, but otherwise has no special purpose. > > > > Hopefully that clarifies the `- 1` here. > > So there are two guard pages at the beginning and only then a page > that holds an object?
Yes, correct.
