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[217.140.110.172]) by mx.google.com with ESMTP id x7si16508653edm.177.2019.07.28.19.59.17 for ; Sun, 28 Jul 2019 19:59:18 -0700 (PDT) Received-SPF: pass (google.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) client-ip=217.140.110.172; Authentication-Results: mx.google.com; spf=pass (google.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=anshuman.khandual@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 1313E344; Sun, 28 Jul 2019 19:59:17 -0700 (PDT) Received: from [10.162.40.126] (p8cg001049571a15.blr.arm.com [10.162.40.126]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 92A103F694; Sun, 28 Jul 2019 19:59:10 -0700 (PDT) Subject: Re: [PATCH v9 19/21] mm: Add generic ptdump To: Steven Price , linux-mm@kvack.org Cc: Andy Lutomirski , Ard Biesheuvel , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Dave Hansen , Ingo Molnar , James Morse , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Peter Zijlstra , Thomas Gleixner , Will Deacon , x86@kernel.org, "H. Peter Anvin" , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Mark Rutland , "Liang, Kan" , Andrew Morton References: <20190722154210.42799-1-steven.price@arm.com> <20190722154210.42799-20-steven.price@arm.com> From: Anshuman Khandual Message-ID: Date: Mon, 29 Jul 2019 08:29:50 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190722154210.42799-20-steven.price@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 07/22/2019 09:12 PM, Steven Price wrote: > Add a generic version of page table dumping that architectures can > opt-in to > > Signed-off-by: Steven Price > --- > include/linux/ptdump.h | 19 +++++ > mm/Kconfig.debug | 21 ++++++ > mm/Makefile | 1 + > mm/ptdump.c | 161 +++++++++++++++++++++++++++++++++++++++++ > 4 files changed, 202 insertions(+) > create mode 100644 include/linux/ptdump.h > create mode 100644 mm/ptdump.c > > diff --git a/include/linux/ptdump.h b/include/linux/ptdump.h > new file mode 100644 > index 000000000000..eb8e78154be3 > --- /dev/null > +++ b/include/linux/ptdump.h > @@ -0,0 +1,19 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > + > +#ifndef _LINUX_PTDUMP_H > +#define _LINUX_PTDUMP_H > + > +struct ptdump_range { > + unsigned long start; > + unsigned long end; > +}; > + > +struct ptdump_state { > + void (*note_page)(struct ptdump_state *st, unsigned long addr, > + int level, unsigned long val); > + const struct ptdump_range *range; > +}; > + > +void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm); > + > +#endif /* _LINUX_PTDUMP_H */ > diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug > index 82b6a20898bd..7ad939b7140f 100644 > --- a/mm/Kconfig.debug > +++ b/mm/Kconfig.debug > @@ -115,3 +115,24 @@ config DEBUG_RODATA_TEST > depends on STRICT_KERNEL_RWX > ---help--- > This option enables a testcase for the setting rodata read-only. > + > +config GENERIC_PTDUMP > + bool > + > +config PTDUMP_CORE > + bool > + > +config PTDUMP_DEBUGFS > + bool "Export kernel pagetable layout to userspace via debugfs" > + depends on DEBUG_KERNEL > + depends on DEBUG_FS > + depends on GENERIC_PTDUMP > + select PTDUMP_CORE So PTDUMP_DEBUGFS depends on GENERIC_PTDUMP but selects PTDUMP_CORE. So any arch subscribing this new generic PTDUMP by selecting GENERIC_PTDUMP needs to provide some functions for PTDUMP_DEBUGFS which does not really have any code in generic MM. Also ptdump_walk_pgd() is wrapped in PTDUMP_CORE not GENERIC_PTDUMP. Then what does PTDUMP_GENERIC really indicate ? Bit confusing here. The new ptdump_walk_pgd() symbol needs to be wrapped in a config symbol for sure which should be selected in all platforms wishing to use it. GENERIC_PTDUMP can be that config. PTDUMP_DEBUGFS will require a full implementation (i.e PTDUMP_CORE) irrespective of whether the platform subscribes GENERIC_PTDUMP or not. It should be something like this. config PTDUMP_DEBUGFS bool "Export kernel pagetable layout to userspace via debugfs" depends on DEBUG_KERNEL depends on DEBUG_FS select PTDUMP_CORE PTDUMP_DEBUGFS need not depend on GENERIC_PTDUMP. All it requires is a PTDUMP_CORE implementation which can optionally use ptdump_walk_pgd() through GENERIC_PTDUMP. s/GENERIC_PTDUMP/PTDUMP_GENERIC to match and group with other configs. DEBUG_WX can also be moved to generic MM like PTDUMP_DEBUGFS ? > + help > + Say Y here if you want to show the kernel pagetable layout in a > + debugfs file. This information is only useful for kernel developers > + who are working in architecture specific areas of the kernel. > + It is probably not a good idea to enable this feature in a production > + kernel. > + > + If in doubt, say N. > diff --git a/mm/Makefile b/mm/Makefile > index 338e528ad436..750a4c12d5da 100644 > --- a/mm/Makefile > +++ b/mm/Makefile > @@ -104,3 +104,4 @@ obj-$(CONFIG_HARDENED_USERCOPY) += usercopy.o > obj-$(CONFIG_PERCPU_STATS) += percpu-stats.o > obj-$(CONFIG_HMM_MIRROR) += hmm.o > obj-$(CONFIG_MEMFD_CREATE) += memfd.o > +obj-$(CONFIG_PTDUMP_CORE) += ptdump.o Should be GENERIC_PTDUMP instead ? > diff --git a/mm/ptdump.c b/mm/ptdump.c > new file mode 100644 > index 000000000000..39befc9088b8 > --- /dev/null > +++ b/mm/ptdump.c > @@ -0,0 +1,161 @@ > +// SPDX-License-Identifier: GPL-2.0 > + > +#include > +#include > +#include > + > +static int ptdump_pgd_entry(pgd_t *pgd, unsigned long addr, > + unsigned long next, struct mm_walk *walk) > +{ > + struct ptdump_state *st = walk->private; > + pgd_t val = READ_ONCE(*pgd); > + > + if (pgd_leaf(val)) > + st->note_page(st, addr, 1, pgd_val(val)); > + > + return 0; > +} > + > +static int ptdump_p4d_entry(p4d_t *p4d, unsigned long addr, > + unsigned long next, struct mm_walk *walk) > +{ > + struct ptdump_state *st = walk->private; > + p4d_t val = READ_ONCE(*p4d); > + > + if (p4d_leaf(val)) > + st->note_page(st, addr, 2, p4d_val(val)); > + > + return 0; > +} > + > +static int ptdump_pud_entry(pud_t *pud, unsigned long addr, > + unsigned long next, struct mm_walk *walk) > +{ > + struct ptdump_state *st = walk->private; > + pud_t val = READ_ONCE(*pud); > + > + if (pud_leaf(val)) > + st->note_page(st, addr, 3, pud_val(val)); > + > + return 0; > +} > + > +static int ptdump_pmd_entry(pmd_t *pmd, unsigned long addr, > + unsigned long next, struct mm_walk *walk) > +{ > + struct ptdump_state *st = walk->private; > + pmd_t val = READ_ONCE(*pmd); > + > + if (pmd_leaf(val)) > + st->note_page(st, addr, 4, pmd_val(val)); > + > + return 0; > +} > + > +static int ptdump_pte_entry(pte_t *pte, unsigned long addr, > + unsigned long next, struct mm_walk *walk) > +{ > + struct ptdump_state *st = walk->private; > + > + st->note_page(st, addr, 5, pte_val(READ_ONCE(*pte))); > + > + return 0; > +} > + > +#ifdef CONFIG_KASAN > +/* > + * This is an optimization for KASAN=y case. Since all kasan page tables > + * eventually point to the kasan_early_shadow_page we could call note_page() > + * right away without walking through lower level page tables. This saves > + * us dozens of seconds (minutes for 5-level config) while checking for > + * W+X mapping or reading kernel_page_tables debugfs file. > + */ > +static inline bool kasan_page_table(struct ptdump_state *st, void *pt, > + unsigned long addr) > +{ > + if (__pa(pt) == __pa(kasan_early_shadow_pmd) || > +#ifdef CONFIG_X86 > + (pgtable_l5_enabled() && > + __pa(pt) == __pa(kasan_early_shadow_p4d)) || > +#endif > + __pa(pt) == __pa(kasan_early_shadow_pud)) { > + st->note_page(st, addr, 5, pte_val(kasan_early_shadow_pte[0])); > + return true; > + } > + return false; > +} > +#else > +static inline bool kasan_page_table(struct ptdump_state *st, void *pt, > + unsigned long addr) > +{ > + return false; > +} > +#endif > + > +static int ptdump_test_p4d(unsigned long addr, unsigned long next, > + p4d_t *p4d, struct mm_walk *walk) > +{ > + struct ptdump_state *st = walk->private; > + > + if (kasan_page_table(st, p4d, addr)) > + return 1; > + return 0; > +} > + > +static int ptdump_test_pud(unsigned long addr, unsigned long next, > + pud_t *pud, struct mm_walk *walk) > +{ > + struct ptdump_state *st = walk->private; > + > + if (kasan_page_table(st, pud, addr)) > + return 1; > + return 0; > +} > + > +static int ptdump_test_pmd(unsigned long addr, unsigned long next, > + pmd_t *pmd, struct mm_walk *walk) > +{ > + struct ptdump_state *st = walk->private; > + > + if (kasan_page_table(st, pmd, addr)) > + return 1; > + return 0; > +} > + > +static int ptdump_hole(unsigned long addr, unsigned long next, > + struct mm_walk *walk) > +{ > + struct ptdump_state *st = walk->private; > + > + st->note_page(st, addr, -1, 0); > + > + return 0; > +} > + > +void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm) > +{ > + struct mm_walk walk = { > + .mm = mm, > + .pgd_entry = ptdump_pgd_entry, > + .p4d_entry = ptdump_p4d_entry, > + .pud_entry = ptdump_pud_entry, > + .pmd_entry = ptdump_pmd_entry, > + .pte_entry = ptdump_pte_entry, > + .test_p4d = ptdump_test_p4d, > + .test_pud = ptdump_test_pud, > + .test_pmd = ptdump_test_pmd, > + .pte_hole = ptdump_hole, > + .private = st > + }; > + const struct ptdump_range *range = st->range; > + > + down_read(&mm->mmap_sem); > + while (range->start != range->end) { > + walk_page_range(range->start, range->end, &walk); > + range++; > + } > + up_read(&mm->mmap_sem); Does walk_page_range() really needed here when it is definitely walking a kernel page table. Why not directly use walk_pgd_range() instead which can save some cycles avoiding going over VMAs, checking for HugeTLB, taking the mmap_sem lock etc. AFAICS only thing it will miss is the opportunity to call walk->test_walk() via walk_page_test(). IIUC test_walk() callback is primarily for testing a VMA for it's eligibility and for kernel page table now there are test callbacks like p?d_test() for individual levels anyway.