From mboxrd@z Thu Jan 1 00:00:00 1970 From: aryabinin@virtuozzo.com (Andrey Ryabinin) Date: Fri, 27 Nov 2015 11:12:28 +0300 Subject: [PATCH RFT] arm64: kasan: Make KASAN work with 16K pages + 48 bit VA In-Reply-To: References: <1448543686-31869-1-git-send-email-aryabinin@virtuozzo.com> Message-ID: <5658106C.10207@virtuozzo.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 11/26/2015 07:40 PM, Ard Biesheuvel wrote: > On 26 November 2015 at 14:14, Andrey Ryabinin 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 >> Signed-off-by: Andrey Ryabinin > > 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.