On Fri, Nov 27, 2015 at 11:12:28AM +0300, Andrey Ryabinin wrote: > On 11/26/2015 07:40 PM, Ard Biesheuvel wrote: > > On 26 November 2015 at 14:14, Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> wrote: > >> Currently kasan assumes that shadow memory covers one or more entire PGDs. > >> That's not true for 16K pages + 48bit VA space, where PGDIR_SIZE is bigger > >> than the whole shadow memory. > >> > >> This patch tries to fix that case. > >> clear_page_tables() is a new replacement of clear_pgs(). Instead of always > >> clearing pgds it clears top level page table entries that entirely belongs > >> to shadow memory. > >> In addition to 'tmp_pg_dir' we now have 'tmp_pud' which is used to store > >> puds that now might be cleared by clear_page_tables. > >> > >> Reported-by: Suzuki K. Poulose <Suzuki.Poulose@xxxxxxx> > >> Signed-off-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> > > > > I would argue that the Kasan code is complicated enough, and we should > > avoid complicating it even further for a configuration that is highly > > theoretical in nature. > > > > In a 16k configuration, the 4th level only adds a single bit of VA > > space (which is, as I understand it, exactly the issue you need to > > address here since the top level page table has only 2 entries and > > hence does not divide by 8 cleanly), which means you are better off > > using 3 levels unless you *really* need more than 128 TB of VA space. > > > > So can't we just live with the limitation, and keep the current code? > > No objections from my side. Let's keep the current code. Ard had a good point, so fine by me as well. -- Catalin -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>