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Date: Fri, 22 Feb 2019 15:01:16 -0800
From: Ralph Campbell <rcampbell@...dia.com>
To: <jglisse@...hat.com>, <linux-mm@...ck.org>,
Andrew Morton <akpm@...ux-foundation.org>
CC: <linux-kernel@...r.kernel.org>,
Christian König <christian.koenig@....com>,
Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
Jani Nikula <jani.nikula@...ux.intel.com>,
Rodrigo Vivi <rodrigo.vivi@...el.com>, Jan Kara <jack@...e.cz>,
Andrea Arcangeli <aarcange@...hat.com>,
Peter Xu <peterx@...hat.com>,
Felix Kuehling <Felix.Kuehling@....com>,
Jason Gunthorpe <jgg@...lanox.com>,
Ross Zwisler <zwisler@...nel.org>,
Dan Williams <dan.j.williams@...el.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Radim Krčmář <rkrcmar@...hat.com>,
Michal Hocko <mhocko@...nel.org>,
John Hubbard <jhubbard@...dia.com>, <kvm@...r.kernel.org>,
<dri-devel@...ts.freedesktop.org>, <linux-rdma@...r.kernel.org>,
Arnd Bergmann <arnd@...db.de>
Subject: 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@...hat.com wrote:
> From: Jérôme Glisse <jglisse@...hat.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@...hat.com>
> Cc: Christian König <christian.koenig@....com>
> Cc: Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>
> Cc: Jani Nikula <jani.nikula@...ux.intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@...el.com>
> Cc: Jan Kara <jack@...e.cz>
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Cc: Peter Xu <peterx@...hat.com>
> Cc: Felix Kuehling <Felix.Kuehling@....com>
> Cc: Jason Gunthorpe <jgg@...lanox.com>
> Cc: Ross Zwisler <zwisler@...nel.org>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Christian Koenig <christian.koenig@....com>
> Cc: Ralph Campbell <rcampbell@...dia.com>
> Cc: John Hubbard <jhubbard@...dia.com>
> Cc: kvm@...r.kernel.org
> Cc: dri-devel@...ts.freedesktop.org
> Cc: linux-rdma@...r.kernel.org
> Cc: Arnd Bergmann <arnd@...db.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@...dia.com>
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