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fs/proc/task_mmu: report SOFT_DIRTY bits through the PAGEMAP_SCAN ioctl

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The PAGEMAP_SCAN ioctl returns information regarding page table entries. 
It is more efficient compared to reading pagemap files.  CRIU can start to
utilize this ioctl, but it needs info about soft-dirty bits to track
memory changes.

We are aware of a new method for tracking memory changes implemented in
the PAGEMAP_SCAN ioctl.  For CRIU, the primary advantage of this method is
its usability by unprivileged users.  However, it is not feasible to
transparently replace the soft-dirty tracker with the new one.  The main
problem here is userfault descriptors that have to be preserved between
pre-dump iterations.  It means criu continues supporting the soft-dirty
method to avoid breakage for current users.  The new method will be
implemented as a separate feature.

[avagin@google.com: update tools/include/uapi/linux/fs.h]
  Link: https://lkml.kernel.org/r/20231107164139.576046-1-avagin@google.com
Link: https://lkml.kernel.org/r/20231106220959.296568-1-avagin@google.com
Signed-off-by: Andrei Vagin <avagin@google.com>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Andrei Vagin 2023-11-06 14:09:58 -08:00 committed by Andrew Morton
parent 8ff252663d
commit e6a9a2cbc1
4 changed files with 19 additions and 1 deletions
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1
Documentation/admin-guide/mm/pagemap.rst
View File

@ -253,6 +253,7 @@ Following flags about pages are currently supported:
- ``PAGE_IS_SWAPPED`` - Page is in swapped
- ``PAGE_IS_PFNZERO`` - Page has zero PFN
- ``PAGE_IS_HUGE`` - Page is THP or Hugetlb backed
- ``PAGE_IS_SOFT_DIRTY`` - Page is soft-dirty
The ``struct pm_scan_arg`` is used as the argument of the IOCTL.

17
fs/proc/task_mmu.c
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@ -1761,7 +1761,7 @@ static int pagemap_release(struct inode *inode, struct file *file)
#define PM_SCAN_CATEGORIES (PAGE_IS_WPALLOWED | PAGE_IS_WRITTEN | \
PAGE_IS_FILE | PAGE_IS_PRESENT | \
PAGE_IS_SWAPPED | PAGE_IS_PFNZERO | \
PAGE_IS_HUGE)
PAGE_IS_HUGE | PAGE_IS_SOFT_DIRTY)
#define PM_SCAN_FLAGS (PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC)
struct pagemap_scan_private {
@ -1793,6 +1793,8 @@ static unsigned long pagemap_page_category(struct pagemap_scan_private *p,
if (is_zero_pfn(pte_pfn(pte)))
categories |= PAGE_IS_PFNZERO;
if (pte_soft_dirty(pte))
categories |= PAGE_IS_SOFT_DIRTY;
} else if (is_swap_pte(pte)) {
swp_entry_t swp;
@ -1806,6 +1808,8 @@ static unsigned long pagemap_page_category(struct pagemap_scan_private *p,
!PageAnon(pfn_swap_entry_to_page(swp)))
categories |= PAGE_IS_FILE;
}
if (pte_swp_soft_dirty(pte))
categories |= PAGE_IS_SOFT_DIRTY;
}
return categories;
@ -1853,12 +1857,16 @@ static unsigned long pagemap_thp_category(struct pagemap_scan_private *p,
if (is_zero_pfn(pmd_pfn(pmd)))
categories |= PAGE_IS_PFNZERO;
if (pmd_soft_dirty(pmd))
categories |= PAGE_IS_SOFT_DIRTY;
} else if (is_swap_pmd(pmd)) {
swp_entry_t swp;
categories |= PAGE_IS_SWAPPED;
if (!pmd_swp_uffd_wp(pmd))
categories |= PAGE_IS_WRITTEN;
if (pmd_swp_soft_dirty(pmd))
categories |= PAGE_IS_SOFT_DIRTY;
if (p->masks_of_interest & PAGE_IS_FILE) {
swp = pmd_to_swp_entry(pmd);
@ -1905,10 +1913,14 @@ static unsigned long pagemap_hugetlb_category(pte_t pte)
categories |= PAGE_IS_FILE;
if (is_zero_pfn(pte_pfn(pte)))
categories |= PAGE_IS_PFNZERO;
if (pte_soft_dirty(pte))
categories |= PAGE_IS_SOFT_DIRTY;
} else if (is_swap_pte(pte)) {
categories |= PAGE_IS_SWAPPED;
if (!pte_swp_uffd_wp_any(pte))
categories |= PAGE_IS_WRITTEN;
if (pte_swp_soft_dirty(pte))
categories |= PAGE_IS_SOFT_DIRTY;
}
return categories;
@ -2007,6 +2019,9 @@ static int pagemap_scan_test_walk(unsigned long start, unsigned long end,
if (wp_allowed)
vma_category |= PAGE_IS_WPALLOWED;
if (vma->vm_flags & VM_SOFTDIRTY)
vma_category |= PAGE_IS_SOFT_DIRTY;
if (!pagemap_scan_is_interesting_vma(vma_category, p))
return 1;

1
include/uapi/linux/fs.h
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@ -316,6 +316,7 @@ typedef int __bitwise __kernel_rwf_t;
#define PAGE_IS_SWAPPED (1 << 4)
#define PAGE_IS_PFNZERO (1 << 5)
#define PAGE_IS_HUGE (1 << 6)
#define PAGE_IS_SOFT_DIRTY (1 << 7)
/*
* struct page_region - Page region with flags

1
tools/include/uapi/linux/fs.h
View File

@ -316,6 +316,7 @@ typedef int __bitwise __kernel_rwf_t;
#define PAGE_IS_SWAPPED (1 << 4)
#define PAGE_IS_PFNZERO (1 << 5)
#define PAGE_IS_HUGE (1 << 6)
#define PAGE_IS_SOFT_DIRTY (1 << 7)
/*
* struct page_region - Page region with flags