Messages in this thread | | | Subject | Re: [PATCH V2 1/2] mm/debug_vm_pgtable/basic: Add validation for dirtiness after write protect | From | Steven Price <> | Date | Wed, 2 Dec 2020 11:16:54 +0000 |
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On 01/12/2020 12:19, Anshuman Khandual wrote: > This adds validation tests for dirtiness after write protect conversion for > each page table level. There are two new separate test types involved here. > > The first test ensures that a given page table entry does not become dirty > after pxx_wrprotect(). This is important for platforms like arm64 which > transfers and drops the hardware dirty bit (!PTE_RDONLY) to the software > dirty bit while making it an write protected one. This test ensures that > no fresh page table entry could be created with hardware dirty bit set. > The second test ensures that a given page table entry always preserve the > dirty information across pxx_wrprotect(). > > This adds two previously missing PUD level basic tests and while here fixes > pxx_wrprotect() related typos in the documentation file. > > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > Suggested-by: Catalin Marinas <catalin.marinas@arm.com> > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> > --- > Documentation/vm/arch_pgtable_helpers.rst | 8 ++--- > mm/debug_vm_pgtable.c | 42 +++++++++++++++++++++++ > 2 files changed, 46 insertions(+), 4 deletions(-) > > diff --git a/Documentation/vm/arch_pgtable_helpers.rst b/Documentation/vm/arch_pgtable_helpers.rst > index f3591ee3aaa8..552567d863b8 100644 > --- a/Documentation/vm/arch_pgtable_helpers.rst > +++ b/Documentation/vm/arch_pgtable_helpers.rst > @@ -50,7 +50,7 @@ PTE Page Table Helpers > +---------------------------+--------------------------------------------------+ > | pte_mkwrite | Creates a writable PTE | > +---------------------------+--------------------------------------------------+ > -| pte_mkwrprotect | Creates a write protected PTE | > +| pte_wrprotect | Creates a write protected PTE | > +---------------------------+--------------------------------------------------+ > | pte_mkspecial | Creates a special PTE | > +---------------------------+--------------------------------------------------+ > @@ -120,7 +120,7 @@ PMD Page Table Helpers > +---------------------------+--------------------------------------------------+ > | pmd_mkwrite | Creates a writable PMD | > +---------------------------+--------------------------------------------------+ > -| pmd_mkwrprotect | Creates a write protected PMD | > +| pmd_wrprotect | Creates a write protected PMD | > +---------------------------+--------------------------------------------------+ > | pmd_mkspecial | Creates a special PMD | > +---------------------------+--------------------------------------------------+ > @@ -186,7 +186,7 @@ PUD Page Table Helpers > +---------------------------+--------------------------------------------------+ > | pud_mkwrite | Creates a writable PUD | > +---------------------------+--------------------------------------------------+ > -| pud_mkwrprotect | Creates a write protected PUD | > +| pud_wrprotect | Creates a write protected PUD | > +---------------------------+--------------------------------------------------+ > | pud_mkdevmap | Creates a ZONE_DEVICE mapped PUD | > +---------------------------+--------------------------------------------------+ > @@ -224,7 +224,7 @@ HugeTLB Page Table Helpers > +---------------------------+--------------------------------------------------+ > | huge_pte_mkwrite | Creates a writable HugeTLB | > +---------------------------+--------------------------------------------------+ > -| huge_pte_mkwrprotect | Creates a write protected HugeTLB | > +| huge_pte_wrprotect | Creates a write protected HugeTLB | > +---------------------------+--------------------------------------------------+ > | huge_ptep_get_and_clear | Clears a HugeTLB | > +---------------------------+--------------------------------------------------+ > diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c > index c05d9dcf7891..c6fffea54522 100644 > --- a/mm/debug_vm_pgtable.c > +++ b/mm/debug_vm_pgtable.c > @@ -63,6 +63,17 @@ static void __init pte_basic_tests(unsigned long pfn, pgprot_t prot) > pte_t pte = pfn_pte(pfn, prot); > > pr_debug("Validating PTE basic\n"); > + > + /* > + * This test needs to execute right after the given page > + * table entry is created with pfn_pte() to make sure that > + * protection_map[idx] does not have the dirty bit enabled > + * from the beginning. This is particularly important for > + * platforms like arm64 where (!PTE_RDONLY) indicate dirty > + * bit being set. > + */
Unless I'm seriously mistaken this comment is misleading - the likes of pte_wrprotect() take the PTE *by value* and return the modified version. So none of these tests actually modify the variable 'pte'. So there shouldn't actually be any restrictions on the ordering.
Or am I missing something?
Steve
> + WARN_ON(pte_dirty(pte_wrprotect(pte))); > + > WARN_ON(!pte_same(pte, pte)); > WARN_ON(!pte_young(pte_mkyoung(pte_mkold(pte)))); > WARN_ON(!pte_dirty(pte_mkdirty(pte_mkclean(pte)))); > @@ -70,6 +81,8 @@ static void __init pte_basic_tests(unsigned long pfn, pgprot_t prot) > WARN_ON(pte_young(pte_mkold(pte_mkyoung(pte)))); > WARN_ON(pte_dirty(pte_mkclean(pte_mkdirty(pte)))); > WARN_ON(pte_write(pte_wrprotect(pte_mkwrite(pte)))); > + WARN_ON(pte_dirty(pte_wrprotect(pte_mkclean(pte)))); > + WARN_ON(!pte_dirty(pte_wrprotect(pte_mkdirty(pte)))); > } > > static void __init pte_advanced_tests(struct mm_struct *mm, > @@ -137,6 +150,18 @@ static void __init pmd_basic_tests(unsigned long pfn, pgprot_t prot) > return; > > pr_debug("Validating PMD basic\n"); > + > + /* > + * This test needs to execute right after the given page > + * table entry is created with pfn_pmd() to make sure that > + * protection_map[idx] does not have the dirty bit enabled > + * from the beginning. This is particularly important for > + * platforms like arm64 where (!PTE_RDONLY) indicate dirty > + * bit being set. > + */ > + WARN_ON(pmd_dirty(pmd_wrprotect(pmd))); > + > + > WARN_ON(!pmd_same(pmd, pmd)); > WARN_ON(!pmd_young(pmd_mkyoung(pmd_mkold(pmd)))); > WARN_ON(!pmd_dirty(pmd_mkdirty(pmd_mkclean(pmd)))); > @@ -144,6 +169,8 @@ static void __init pmd_basic_tests(unsigned long pfn, pgprot_t prot) > WARN_ON(pmd_young(pmd_mkold(pmd_mkyoung(pmd)))); > WARN_ON(pmd_dirty(pmd_mkclean(pmd_mkdirty(pmd)))); > WARN_ON(pmd_write(pmd_wrprotect(pmd_mkwrite(pmd)))); > + WARN_ON(pmd_dirty(pmd_wrprotect(pmd_mkclean(pmd)))); > + WARN_ON(!pmd_dirty(pmd_wrprotect(pmd_mkdirty(pmd)))); > /* > * A huge page does not point to next level page table > * entry. Hence this must qualify as pmd_bad(). > @@ -257,11 +284,26 @@ static void __init pud_basic_tests(unsigned long pfn, pgprot_t prot) > return; > > pr_debug("Validating PUD basic\n"); > + > + /* > + * This test needs to execute right after the given page > + * table entry is created with pfn_pud() to make sure that > + * protection_map[idx] does not have the dirty bit enabled > + * from the beginning. This is particularly important for > + * platforms like arm64 where (!PTE_RDONLY) indicate dirty > + * bit being set. > + */ > + WARN_ON(pud_dirty(pud_wrprotect(pud))); > + > WARN_ON(!pud_same(pud, pud)); > WARN_ON(!pud_young(pud_mkyoung(pud_mkold(pud)))); > + WARN_ON(!pud_dirty(pud_mkdirty(pud_mkclean(pud)))); > + WARN_ON(pud_dirty(pud_mkclean(pud_mkdirty(pud)))); > WARN_ON(!pud_write(pud_mkwrite(pud_wrprotect(pud)))); > WARN_ON(pud_write(pud_wrprotect(pud_mkwrite(pud)))); > WARN_ON(pud_young(pud_mkold(pud_mkyoung(pud)))); > + WARN_ON(pud_dirty(pud_wrprotect(pud_mkclean(pud)))); > + WARN_ON(!pud_dirty(pud_wrprotect(pud_mkdirty(pud)))); > > if (mm_pmd_folded(mm)) > return; >
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