From: Zi Yan <ziy@nvidia.com>
To: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: <linux-mm@kvack.org>, <christophe.leroy@c-s.fr>,
Andrew Morton <akpm@linux-foundation.org>,
Mike Rapoport <rppt@linux.ibm.com>,
Vineet Gupta <vgupta@synopsys.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
"Kirill A . Shutemov" <kirill@shutemov.name>,
Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
<linux-snps-arc@lists.infradead.org>,
<linux-arm-kernel@lists.infradead.org>,
<linuxppc-dev@lists.ozlabs.org>, <linux-s390@vger.kernel.org>,
<linux-riscv@lists.infradead.org>, <x86@kernel.org>,
<linux-arch@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH V2 1/3] mm/debug: Add tests validating arch page table helpers for core features
Date: Thu, 26 Mar 2020 13:08:34 -0400 [thread overview]
Message-ID: <CEB780BF-ECB6-4304-8C04-3DCBAF931492@nvidia.com> (raw)
In-Reply-To: <5b188e44-73d5-673c-8df1-f2c42b556cf9@arm.com>
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On 25 Mar 2020, at 22:18, Anshuman Khandual wrote:
> External email: Use caution opening links or attachments
>
>
> On 03/24/2020 06:59 PM, Zi Yan wrote:
>> On 24 Mar 2020, at 1:22, Anshuman Khandual wrote:
>>
>>> This adds new tests validating arch page table helpers for these following
>>> core memory features. These tests create and test specific mapping types at
>>> various page table levels.
>>>
>>> 1. SPECIAL mapping
>>> 2. PROTNONE mapping
>>> 3. DEVMAP mapping
>>> 4. SOFTDIRTY mapping
>>> 5. SWAP mapping
>>> 6. MIGRATION mapping
>>> 7. HUGETLB mapping
>>> 8. THP mapping
>>>
>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>> Cc: Mike Rapoport <rppt@linux.ibm.com>
>>> Cc: Vineet Gupta <vgupta@synopsys.com>
>>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>>> Cc: Will Deacon <will@kernel.org>
>>> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
>>> Cc: Paul Mackerras <paulus@samba.org>
>>> Cc: Michael Ellerman <mpe@ellerman.id.au>
>>> Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
>>> Cc: Vasily Gorbik <gor@linux.ibm.com>
>>> Cc: Christian Borntraeger <borntraeger@de.ibm.com>
>>> Cc: Thomas Gleixner <tglx@linutronix.de>
>>> Cc: Ingo Molnar <mingo@redhat.com>
>>> Cc: Borislav Petkov <bp@alien8.de>
>>> Cc: "H. Peter Anvin" <hpa@zytor.com>
>>> Cc: Kirill A. Shutemov <kirill@shutemov.name>
>>> Cc: Paul Walmsley <paul.walmsley@sifive.com>
>>> Cc: Palmer Dabbelt <palmer@dabbelt.com>
>>> Cc: linux-snps-arc@lists.infradead.org
>>> Cc: linux-arm-kernel@lists.infradead.org
>>> Cc: linuxppc-dev@lists.ozlabs.org
>>> Cc: linux-s390@vger.kernel.org
>>> Cc: linux-riscv@lists.infradead.org
>>> Cc: x86@kernel.org
>>> Cc: linux-arch@vger.kernel.org
>>> Cc: linux-kernel@vger.kernel.org
>>> Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
>>> ---
>>> mm/debug_vm_pgtable.c | 291 +++++++++++++++++++++++++++++++++++++++++-
>>> 1 file changed, 290 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
>>> index 98990a515268..15055a8f6478 100644
>>> --- a/mm/debug_vm_pgtable.c
>>> +++ b/mm/debug_vm_pgtable.c
>>> @@ -289,6 +289,267 @@ static void __init pmd_populate_tests(struct mm_struct *mm, pmd_t *pmdp,
>>> WARN_ON(pmd_bad(pmd));
>>> }
>>>
>>> +static void __init pte_special_tests(unsigned long pfn, pgprot_t prot)
>>> +{
>>> + pte_t pte = pfn_pte(pfn, prot);
>>> +
>>> + if (!IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL))
>>> + return;
>>> +
>>> + WARN_ON(!pte_special(pte_mkspecial(pte)));
>>> +}
>>> +
>>> +static void __init pte_protnone_tests(unsigned long pfn, pgprot_t prot)
>>> +{
>>> + pte_t pte = pfn_pte(pfn, prot);
>>> +
>>> + if (!IS_ENABLED(CONFIG_NUMA_BALANCING))
>>> + return;
>>> +
>>> + WARN_ON(!pte_protnone(pte));
>>> + WARN_ON(!pte_present(pte));
>>> +}
>>> +
>>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>> +static void __init pmd_protnone_tests(unsigned long pfn, pgprot_t prot)
>>> +{
>>> + pmd_t pmd = pfn_pmd(pfn, prot);
>>> +
>>> + if (!IS_ENABLED(CONFIG_NUMA_BALANCING))
>>> + return;
>>> +
>>> + WARN_ON(!pmd_protnone(pmd));
>>> + WARN_ON(!pmd_present(pmd));
>>> +}
>>> +#else
>>> +static void __init pmd_protnone_tests(unsigned long pfn, pgprot_t prot) { }
>>> +#endif
>>> +
>>> +#ifdef CONFIG_ARCH_HAS_PTE_DEVMAP
>>> +static void __init pte_devmap_tests(unsigned long pfn, pgprot_t prot)
>>> +{
>>> + pte_t pte = pfn_pte(pfn, prot);
>>> +
>>> + WARN_ON(!pte_devmap(pte_mkdevmap(pte)));
>>> +}
>>> +
>>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>> +static void __init pmd_devmap_tests(unsigned long pfn, pgprot_t prot)
>>> +{
>>> + pmd_t pmd = pfn_pmd(pfn, prot);
>>> +
>>> + WARN_ON(!pmd_devmap(pmd_mkdevmap(pmd)));
>>> +}
>>> +
>>> +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
>>> +static void __init pud_devmap_tests(unsigned long pfn, pgprot_t prot)
>>> +{
>>> + pud_t pud = pfn_pud(pfn, prot);
>>> +
>>> + WARN_ON(!pud_devmap(pud_mkdevmap(pud)));
>>> +}
>>> +#else
>>> +static void __init pud_devmap_tests(unsigned long pfn, pgprot_t prot) { }
>>> +#endif
>>> +#else
>>> +static void __init pmd_devmap_tests(unsigned long pfn, pgprot_t prot) { }
>>> +static void __init pud_devmap_tests(unsigned long pfn, pgprot_t prot) { }
>>> +#endif
>>> +#else
>>> +static void __init pte_devmap_tests(unsigned long pfn, pgprot_t prot) { }
>>> +static void __init pmd_devmap_tests(unsigned long pfn, pgprot_t prot) { }
>>> +static void __init pud_devmap_tests(unsigned long pfn, pgprot_t prot) { }
>>> +#endif
>>> +
>>> +static void __init pte_soft_dirty_tests(unsigned long pfn, pgprot_t prot)
>>> +{
>>> + pte_t pte = pfn_pte(pfn, prot);
>>> +
>>> + if (!IS_ENABLED(CONFIG_HAVE_ARCH_SOFT_DIRTY))
>>> + return;
>>> +
>>> + WARN_ON(!pte_soft_dirty(pte_mksoft_dirty(pte)));
>>> + WARN_ON(pte_soft_dirty(pte_clear_soft_dirty(pte)));
>>> +}
>>> +
>>> +static void __init pte_swap_soft_dirty_tests(unsigned long pfn, pgprot_t prot)
>>> +{
>>> + pte_t pte = pfn_pte(pfn, prot);
>>> +
>>> + if (!IS_ENABLED(CONFIG_HAVE_ARCH_SOFT_DIRTY))
>>> + return;
>>> +
>>> + WARN_ON(!pte_swp_soft_dirty(pte_swp_mksoft_dirty(pte)));
>>> + WARN_ON(pte_swp_soft_dirty(pte_swp_clear_soft_dirty(pte)));
>>> +}
>>> +
>>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>> +static void __init pmd_soft_dirty_tests(unsigned long pfn, pgprot_t prot)
>>> +{
>>> + pmd_t pmd = pfn_pmd(pfn, prot);
>>> +
>>> + if (!IS_ENABLED(CONFIG_HAVE_ARCH_SOFT_DIRTY))
>>> + return;
>>> +
>>> + WARN_ON(!pmd_soft_dirty(pmd_mksoft_dirty(pmd)));
>>> + WARN_ON(pmd_soft_dirty(pmd_clear_soft_dirty(pmd)));
>>> +}
>>> +
>>> +static void __init pmd_swap_soft_dirty_tests(unsigned long pfn, pgprot_t prot)
>>> +{
>>> + pmd_t pmd = pfn_pmd(pfn, prot);
>>> +
>>> + if (!IS_ENABLED(CONFIG_HAVE_ARCH_SOFT_DIRTY) ||
>>> + !IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION))
>>> + return;
>>> +
>>> + WARN_ON(!pmd_swp_soft_dirty(pmd_swp_mksoft_dirty(pmd)));
>>> + WARN_ON(pmd_swp_soft_dirty(pmd_swp_clear_soft_dirty(pmd)));
>>> +}
>>> +#else
>>> +static void __init pmd_soft_dirty_tests(unsigned long pfn, pgprot_t prot) { }
>>> +static void __init pmd_swap_soft_dirty_tests(unsigned long pfn, pgprot_t prot)
>>> +{
>>> +}
>>> +#endif
>>> +
>>> +static void __init pte_swap_tests(unsigned long pfn, pgprot_t prot)
>>> +{
>>> + swp_entry_t swp;
>>> + pte_t pte;
>>> +
>>> + pte = pfn_pte(pfn, prot);
>>> + swp = __pte_to_swp_entry(pte);
>>> + WARN_ON(!pte_same(pte, __swp_entry_to_pte(swp)));
>>> +}
>>> +
>>> +#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
>>> +static void __init pmd_swap_tests(unsigned long pfn, pgprot_t prot)
>>> +{
>>> + swp_entry_t swp;
>>> + pmd_t pmd;
>>> +
>>> + pmd = pfn_pmd(pfn, prot);
>>> + swp = __pmd_to_swp_entry(pmd);
>>> + WARN_ON(!pmd_same(pmd, __swp_entry_to_pmd(swp)));
>>> +}
>>> +#else
>>> +static void __init pmd_swap_tests(unsigned long pfn, pgprot_t prot) { }
>>> +#endif
>>> +
>>> +static void __init swap_migration_tests(void)
>>> +{
>>> + struct page *page;
>>> + swp_entry_t swp;
>>> +
>>> + if (!IS_ENABLED(CONFIG_MIGRATION))
>>> + return;
>>> + /*
>>> + * swap_migration_tests() requires a dedicated page as it needs to
>>> + * be locked before creating a migration entry from it. Locking the
>>> + * page that actually maps kernel text ('start_kernel') can be real
>>> + * problematic. Lets allocate a dedicated page explicitly for this
>>> + * purpose that will be freed subsequently.
>>> + */
>>> + page = alloc_page(GFP_KERNEL);
>>> + if (!page) {
>>> + pr_err("page allocation failed\n");
>>> + return;
>>> + }
>>> +
>>> + /*
>>> + * make_migration_entry() expects given page to be
>>> + * locked, otherwise it stumbles upon a BUG_ON().
>>> + */
>>> + __SetPageLocked(page);
>>> + swp = make_migration_entry(page, 1);
>>> + WARN_ON(!is_migration_entry(swp));
>>> + WARN_ON(!is_write_migration_entry(swp));
>>> +
>>> + make_migration_entry_read(&swp);
>>> + WARN_ON(!is_migration_entry(swp));
>>> + WARN_ON(is_write_migration_entry(swp));
>>> +
>>> + swp = make_migration_entry(page, 0);
>>> + WARN_ON(!is_migration_entry(swp));
>>> + WARN_ON(is_write_migration_entry(swp));
>>> + __ClearPageLocked(page);
>>> + __free_page(page);
>>> +}
>>> +
>>> +#ifdef CONFIG_HUGETLB_PAGE
>>> +static void __init hugetlb_basic_tests(unsigned long pfn, pgprot_t prot)
>>> +{
>>> + struct page *page;
>>> + pte_t pte;
>>> +
>>> + /*
>>> + * Accessing the page associated with the pfn is safe here,
>>> + * as it was previously derived from a real kernel symbol.
>>> + */
>>> + page = pfn_to_page(pfn);
>>> + pte = mk_huge_pte(page, prot);
>>> +
>>> + WARN_ON(!huge_pte_dirty(huge_pte_mkdirty(pte)));
>>> + WARN_ON(!huge_pte_write(huge_pte_mkwrite(huge_pte_wrprotect(pte))));
>>> + WARN_ON(huge_pte_write(huge_pte_wrprotect(huge_pte_mkwrite(pte))));
>>> +
>>> +#ifdef CONFIG_ARCH_WANT_GENERAL_HUGETLB
>>> + pte = pfn_pte(pfn, prot);
>>> +
>>> + WARN_ON(!pte_huge(pte_mkhuge(pte)));
>>> +#endif
>>> +}
>>> +#else
>>> +static void __init hugetlb_basic_tests(unsigned long pfn, pgprot_t prot) { }
>>> +#endif
>>> +
>>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>> +static void __init pmd_thp_tests(unsigned long pfn, pgprot_t prot)
>>> +{
>>> + pmd_t pmd;
>>> +
>>> + /*
>>> + * pmd_trans_huge() and pmd_present() must return positive
>>> + * after MMU invalidation with pmd_mknotpresent().
>>> + */
>>> + pmd = pfn_pmd(pfn, prot);
>>> + WARN_ON(!pmd_trans_huge(pmd_mkhuge(pmd)));
>>> +
>>> +#ifndef __HAVE_ARCH_PMDP_INVALIDATE
>>> + WARN_ON(!pmd_trans_huge(pmd_mknotpresent(pmd_mkhuge(pmd))));
>>> + WARN_ON(!pmd_present(pmd_mknotpresent(pmd_mkhuge(pmd))));
>>> +#endif
>>
>> I think we need a better comment here, because requiring pmd_trans_huge() and
>> pmd_present() returning true after pmd_mknotpresent() is not straightforward.
>
> Thats right.
>
>>
>> According to Andrea Arcangeli’s email (https://lore.kernel.org/linux-mm/20181017020930.GN30832@redhat.com/),
>> This behavior is an optimization for transparent huge page.
>> pmd_trans_huge() must be true if pmd_page() returns you a valid THP to avoid
>> taking the pmd_lock when others walk over non transhuge pmds (i.e. there are no
>> THP allocated). Especially when we split a THP, removing the present bit from
>> the pmd, pmd_trans_huge() still needs to return true. pmd_present() should
>> be true whenever pmd_trans_huge() returns true.
>
> Sure, will modify the existing comment here like this.
>
> /*
> * pmd_trans_huge() and pmd_present() must return positive after
> * MMU invalidation with pmd_mknotpresent(). This behavior is an
> * optimization for transparent huge page. pmd_trans_huge() must
> * be true if pmd_page() returns a valid THP to avoid taking the
> * pmd_lock when others walk over non transhuge pmds (i.e. there
> * are no THP allocated). Especially when splitting a THP and
> * removing the present bit from the pmd, pmd_trans_huge() still
> * needs to return true. pmd_present() should be true whenever
> * pmd_trans_huge() returns true.
> */
>
>>
>> I think it is also worth either putting Andres’s email or the link to it
>> in the rst file in your 3rd patch. It is a good documentation for this special
>> case.
>
> Makes sense. Will update Andrea's email link in the .rst file as well.
>
Look good to me. Thanks.
Reviewed-by: Zi Yan <ziy@nvidia.com>
—
Best Regards,
Yan Zi
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next prev parent reply other threads:[~2020-03-26 17:08 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-24 5:22 [PATCH V2 0/3] mm/debug: Add more arch page table helper tests Anshuman Khandual
2020-03-24 5:22 ` [PATCH V2 1/3] mm/debug: Add tests validating arch page table helpers for core features Anshuman Khandual
2020-03-24 13:29 ` Zi Yan
2020-03-26 2:18 ` Anshuman Khandual
2020-03-26 17:08 ` Zi Yan [this message]
2020-03-30 8:56 ` [mm/debug] f675f2f91d: WARNING:at_mm/debug_vm_pgtable.c:#debug_vm_pgtable kernel test robot
2020-04-05 14:49 ` Anshuman Khandual
2020-03-24 5:22 ` [PATCH V2 2/3] mm/debug: Add tests validating arch advanced page table helpers Anshuman Khandual
2020-03-27 7:41 ` [mm/debug] d157503f6f: WARNING:at_mm/debug_vm_pgtable.c:#debug_vm_pgtable kernel test robot
2020-03-24 5:22 ` [PATCH V2 3/3] Documentation/mm: Add descriptions for arch page table helpers Anshuman Khandual
2020-03-26 2:23 ` [PATCH V2 0/3] mm/debug: Add more arch page table helper tests Anshuman Khandual
2020-03-26 15:23 ` Christophe Leroy
2020-03-27 6:46 ` Anshuman Khandual
2020-03-27 7:00 ` Christophe Leroy
2020-03-29 14:21 ` Anshuman Khandual
2020-03-31 12:30 ` Gerald Schaefer
2020-04-05 12:28 ` Anshuman Khandual
2020-04-07 15:54 ` Gerald Schaefer
2020-04-08 7:11 ` Anshuman Khandual
2020-04-08 12:15 ` Gerald Schaefer
2020-04-09 1:06 ` Anshuman Khandual
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