From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f46.google.com (mail-pa0-f46.google.com [209.85.220.46]) by kanga.kvack.org (Postfix) with ESMTP id EF37F6B0256 for ; Tue, 11 Aug 2015 12:40:17 -0400 (EDT) Received: by pacrr5 with SMTP id rr5so131210460pac.3 for ; Tue, 11 Aug 2015 09:40:17 -0700 (PDT) Received: from foss.arm.com (foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id gt1si4372879pac.153.2015.08.11.09.40.16 for ; Tue, 11 Aug 2015 09:40:17 -0700 (PDT) Date: Tue, 11 Aug 2015 17:40:11 +0100 From: Catalin Marinas Subject: Re: [PATCH v5 2/6] x86/kasan, mm: introduce generic kasan_populate_zero_shadow() Message-ID: <20150811164010.GJ23307@e104818-lin.cambridge.arm.com> References: <1439259499-13913-1-git-send-email-ryabinin.a.a@gmail.com> <1439259499-13913-3-git-send-email-ryabinin.a.a@gmail.com> <20150811154117.GH23307@e104818-lin.cambridge.arm.com> <55CA21E8.2060704@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55CA21E8.2060704@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Andrey Ryabinin Cc: "H. Peter Anvin" , Yury , Arnd Bergmann , linux-mm@kvack.org, Linus Walleij , x86@kernel.org, Will Deacon , linux-kernel@vger.kernel.org, Alexey Klimov , Ingo Molnar , Alexander Potapenko , "Aneesh Kumar K.V" , David Keitel , Dmitry Vyukov , Andrew Morton , Thomas Gleixner , linux-arm-kernel@lists.infradead.org On Tue, Aug 11, 2015 at 07:25:12PM +0300, Andrey Ryabinin wrote: > On 08/11/2015 06:41 PM, Catalin Marinas wrote: > > On Tue, Aug 11, 2015 at 05:18:15AM +0300, Andrey Ryabinin wrote: > >> --- /dev/null > >> +++ b/mm/kasan/kasan_init.c > > [...] > >> +#if CONFIG_PGTABLE_LEVELS > 3 > >> +pud_t kasan_zero_pud[PTRS_PER_PUD] __page_aligned_bss; > >> +#endif > >> +#if CONFIG_PGTABLE_LEVELS > 2 > >> +pmd_t kasan_zero_pmd[PTRS_PER_PMD] __page_aligned_bss; > >> +#endif > >> +pte_t kasan_zero_pte[PTRS_PER_PTE] __page_aligned_bss; > > > > Is there any problem if you don't add the #ifs here? Wouldn't the linker > > remove them if they are not used? > > > Original hunk copied here for easy comparison: > > > >> -static int __init zero_pte_populate(pmd_t *pmd, unsigned long addr, > >> - unsigned long end) > >> -{ > >> - pte_t *pte = pte_offset_kernel(pmd, addr); > >> - > >> - while (addr + PAGE_SIZE <= end) { > >> - WARN_ON(!pte_none(*pte)); > >> - set_pte(pte, __pte(__pa_nodebug(kasan_zero_page) > >> - | __PAGE_KERNEL_RO)); > >> - addr += PAGE_SIZE; > >> - pte = pte_offset_kernel(pmd, addr); > >> - } > >> - return 0; > >> -} > > [...] > >> +static void __init zero_pte_populate(pmd_t *pmd, unsigned long addr, > >> + unsigned long end) > >> +{ > >> + pte_t *pte = pte_offset_kernel(pmd, addr); > >> + pte_t zero_pte; > >> + > >> + zero_pte = pfn_pte(PFN_DOWN(__pa(kasan_zero_page)), PAGE_KERNEL); > >> + zero_pte = pte_wrprotect(zero_pte); > >> + > >> + while (addr + PAGE_SIZE <= end) { > >> + set_pte_at(&init_mm, addr, pte, zero_pte); > >> + addr += PAGE_SIZE; > >> + pte = pte_offset_kernel(pmd, addr); > >> + } > >> +} > > > > I think there are some differences with the original x86 code. The first > > one is the use of __pa_nodebug, does it cause any problems if > > CONFIG_DEBUG_VIRTUAL is enabled? > > __pa_nodebug() should be used before kasan_early_init(), this piece of code > executed far later, so it's ok to use __pa() here. > This was actually a mistake in original code to use __pa_nodebug(). OK. So please add a comment in the commit log. > > The second is the use of a read-only attribute when mapping > > kasan_zero_page on x86. Can it cope with a writable mapping? > > > > Did you miss this line: > > + zero_pte = pte_wrprotect(zero_pte); Ah, yes, I missed this. Anyway, for this patch: Acked-by: Catalin Marinas Not sure how you plan to merge it though since there are x86 dependencies. I could send the whole series via tip or the mm tree (and I guess it's pretty late for 4.3). -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org