Re: [PATCH v5 9/9] mm/mmu_notifier: set MMU_NOTIFIER_USE_CHANGE_PTE flag where appropriate v2

On 2/19/19 12:04 PM, jglisse@redhat.com wrote:

From: Jérôme Glisse jglisse@redhat.com

When notifying change for a range use MMU_NOTIFIER_USE_CHANGE_PTE flag for page table update that use set_pte_at_notify() and where the we are going either from read and write to read only with same pfn or read only to read and write with new pfn.

Note that set_pte_at_notify() itself should only be use in rare cases ie we do not want to use it when we are updating a significant range of virtual addresses and thus a significant number of pte. Instead for those cases the event provided to mmu notifer invalidate_range_start() callback should be use for optimization.

Changes since v1: - Use the new unsigned flags field in struct mmu_notifier_range - Use the new flags parameter to mmu_notifier_range_init() - Explicitly list all the patterns where we can use change_pte()

Signed-off-by: Jérôme Glisse jglisse@redhat.com Cc: Christian König christian.koenig@amd.com Cc: Joonas Lahtinen joonas.lahtinen@linux.intel.com Cc: Jani Nikula jani.nikula@linux.intel.com Cc: Rodrigo Vivi rodrigo.vivi@intel.com Cc: Jan Kara jack@suse.cz Cc: Andrea Arcangeli aarcange@redhat.com Cc: Peter Xu peterx@redhat.com Cc: Felix Kuehling Felix.Kuehling@amd.com Cc: Jason Gunthorpe jgg@mellanox.com Cc: Ross Zwisler zwisler@kernel.org Cc: Dan Williams dan.j.williams@intel.com Cc: Paolo Bonzini pbonzini@redhat.com Cc: Radim Krčmář rkrcmar@redhat.com Cc: Michal Hocko mhocko@kernel.org Cc: Christian Koenig christian.koenig@amd.com Cc: Ralph Campbell rcampbell@nvidia.com Cc: John Hubbard jhubbard@nvidia.com Cc: kvm@vger.kernel.org Cc: dri-devel@lists.freedesktop.org Cc: linux-rdma@vger.kernel.org Cc: Arnd Bergmann arnd@arndb.de

---

include/linux/mmu_notifier.h | 34 ++++++++++++++++++++++++++++++++-- mm/ksm.c | 11 ++++++----- mm/memory.c | 5 +++-- 3 files changed, 41 insertions(+), 9 deletions(-)

diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h index b6c004bd9f6a..0230a4b06b46 100644 --- a/include/linux/mmu_notifier.h +++ b/include/linux/mmu_notifier.h @@ -40,6 +40,26 @@ enum mmu_notifier_event { MMU_NOTIFY_SOFT_DIRTY, };

+/*

• • @MMU_NOTIFIER_RANGE_BLOCKABLE: can the mmu notifier range_start/range_end
• • callback block or not ? If set then the callback can block.
• • @MMU_NOTIFIER_USE_CHANGE_PTE: only set when the page table it updated with
• • the set_pte_at_notify() the valid patterns for this are:

• •  - pte read and write to read only same pfn
    

• •  - pte read only to read and write (pfn can change or stay the same)
    

• •  - pte read only to read only with different pfn
    

• • It is illegal to set in any other circumstances.
• • Note that set_pte_at_notify() should not be use outside of the above cases.
• • When updating a range in batch (like write protecting a range) it is better
• • to rely on invalidate_range_start() and struct mmu_notifier_range to infer
• • the kind of update that is happening (as an example you can look at the
• • mmu_notifier_range_update_to_read_only() function).
• */

+#define MMU_NOTIFIER_RANGE_BLOCKABLE (1 << 0) +#define MMU_NOTIFIER_USE_CHANGE_PTE (1 << 1)

• #ifdef CONFIG_MMU_NOTIFIER

  /*

@@ -55,8 +75,6 @@ struct mmu_notifier_mm { spinlock_t lock; };

-#define MMU_NOTIFIER_RANGE_BLOCKABLE (1 << 0)

• struct mmu_notifier_range { struct vm_area_struct *vma; struct mm_struct *mm;

@@ -268,6 +286,12 @@ mmu_notifier_range_blockable(const struct mmu_notifier_range *range) return (range->flags & MMU_NOTIFIER_RANGE_BLOCKABLE); }

+static inline bool +mmu_notifier_range_use_change_pte(const struct mmu_notifier_range *range) +{

• return (range->flags & MMU_NOTIFIER_USE_CHANGE_PTE);

+}

• static inline void mmu_notifier_release(struct mm_struct *mm) { if (mm_has_notifiers(mm))

@@ -509,6 +533,12 @@ mmu_notifier_range_blockable(const struct mmu_notifier_range *range) return true; }

+static inline bool +mmu_notifier_range_use_change_pte(const struct mmu_notifier_range *range) +{

• return false;

+}

• static inline int mm_has_notifiers(struct mm_struct *mm) { return 0;

diff --git a/mm/ksm.c b/mm/ksm.c index b782fadade8f..41e51882f999 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -1066,9 +1066,9 @@ static int write_protect_page(struct vm_area_struct *vma, struct page *page,

BUG_ON(PageTransCompound(page));

• mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm,

• 		pvmw.address,
  

• 		pvmw.address + PAGE_SIZE);
  

• mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR,

• 		MMU_NOTIFIER_USE_CHANGE_PTE, vma, mm,
  

• 		pvmw.address, pvmw.address + PAGE_SIZE);
  

  mmu_notifier_invalidate_range_start(&range);

  if (!page_vma_mapped_walk(&pvmw))

@@ -1155,8 +1155,9 @@ static int replace_page(struct vm_area_struct *vma, struct page *page, if (!pmd) goto out;

• mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm, addr,

• 		addr + PAGE_SIZE);
  

• mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR,

• 		MMU_NOTIFIER_USE_CHANGE_PTE,
  

• 		vma, mm, addr, addr + PAGE_SIZE);
  

  mmu_notifier_invalidate_range_start(&range);

  ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);

diff --git a/mm/memory.c b/mm/memory.c index 45dbc174a88c..cb71d3ff1b97 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2282,8 +2282,9 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)

__SetPageUptodate(new_page);

• mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm,

• 		vmf->address & PAGE_MASK,
  

• mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR,

• 		MMU_NOTIFIER_USE_CHANGE_PTE,
  

• 		vma, mm, vmf->address & PAGE_MASK,
  	(vmf->address & PAGE_MASK) + PAGE_SIZE);
  

  mmu_notifier_invalidate_range_start(&range);

Reviewed-by: Ralph Campbell rcampbell@nvidia.com