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mm: pagewalk: add p4d_entry() and pgd_entry()
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pgd_entry() and pud_entry() were removed by commit 0b1fbfe
("mm/pagewalk: remove pgd_entry() and pud_entry()") because there were no
users.  We're about to add users so reintroduce them, along with
p4d_entry() as we now have 5 levels of tables.

Note that commit a00cc7d ("mm, x86: add support for PUD-sized
transparent hugepages") already re-added pud_entry() but with different
semantics to the other callbacks.  This commit reverts the semantics back
to match the other callbacks.

To support hmm.c which now uses the new semantics of pud_entry() a new
member ('action') of struct mm_walk is added which allows the callbacks to
either descend (ACTION_SUBTREE, the default), skip (ACTION_CONTINUE) or
repeat the callback (ACTION_AGAIN).  hmm.c is then updated to call
pud_trans_huge_lock() itself and make use of the splitting/retry logic of
the core code.

After this change pud_entry() is called for all entries, not just
transparent huge pages.

[[email protected]: fix unused variable warning]
 Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Steven Price <[email protected]>
Signed-off-by: Arnd Bergmann <[email protected]>
Cc: Albert Ou <[email protected]>
Cc: Alexandre Ghiti <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Christian Borntraeger <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: James Hogan <[email protected]>
Cc: James Morse <[email protected]>
Cc: Jerome Glisse <[email protected]>
Cc: "Liang, Kan" <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Paul Burton <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Paul Walmsley <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Russell King <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vasily Gorbik <[email protected]>
Cc: Vineet Gupta <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Zong Li <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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@torvalds
Steven Price authored and torvalds committed Feb 4, 2020
1 parent 757b2a4 commit 3afc423
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Showing 3 changed files with 95 additions and 47 deletions.
34 changes: 28 additions & 6 deletions include/linux/pagewalk.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -8,15 +8,15 @@ struct mm_walk;

/**
* mm_walk_ops - callbacks for walk_page_range
* @pud_entry: if set, called for each non-empty PUD (2nd-level) entry
* this handler should only handle pud_trans_huge() puds.
* the pmd_entry or pte_entry callbacks will be used for
* regular PUDs.
* @pmd_entry: if set, called for each non-empty PMD (3rd-level) entry
* @pgd_entry: if set, called for each non-empty PGD (top-level) entry
* @p4d_entry: if set, called for each non-empty P4D entry
* @pud_entry: if set, called for each non-empty PUD entry
* @pmd_entry: if set, called for each non-empty PMD entry
* this handler is required to be able to handle
* pmd_trans_huge() pmds. They may simply choose to
* split_huge_page() instead of handling it explicitly.
* @pte_entry: if set, called for each non-empty PTE (4th-level) entry
* @pte_entry: if set, called for each non-empty PTE (lowest-level)
* entry
* @pte_hole: if set, called for each hole at all levels
* @hugetlb_entry: if set, called for each hugetlb entry
* @test_walk: caller specific callback function to determine whether
Expand All @@ -27,8 +27,15 @@ struct mm_walk;
* @pre_vma: if set, called before starting walk on a non-null vma.
* @post_vma: if set, called after a walk on a non-null vma, provided
* that @pre_vma and the vma walk succeeded.
*
* p?d_entry callbacks are called even if those levels are folded on a
* particular architecture/configuration.
*/
struct mm_walk_ops {
int (*pgd_entry)(pgd_t *pgd, unsigned long addr,
unsigned long next, struct mm_walk *walk);
int (*p4d_entry)(p4d_t *p4d, unsigned long addr,
unsigned long next, struct mm_walk *walk);
int (*pud_entry)(pud_t *pud, unsigned long addr,
unsigned long next, struct mm_walk *walk);
int (*pmd_entry)(pmd_t *pmd, unsigned long addr,
Expand All @@ -47,11 +54,25 @@ struct mm_walk_ops {
void (*post_vma)(struct mm_walk *walk);
};

/*
* Action for pud_entry / pmd_entry callbacks.
* ACTION_SUBTREE is the default
*/
enum page_walk_action {
/* Descend to next level, splitting huge pages if needed and possible */
ACTION_SUBTREE = 0,
/* Continue to next entry at this level (ignoring any subtree) */
ACTION_CONTINUE = 1,
/* Call again for this entry */
ACTION_AGAIN = 2
};

/**
* mm_walk - walk_page_range data
* @ops: operation to call during the walk
* @mm: mm_struct representing the target process of page table walk
* @vma: vma currently walked (NULL if walking outside vmas)
* @action: next action to perform (see enum page_walk_action)
* @private: private data for callbacks' usage
*
* (see the comment on walk_page_range() for more details)
Expand All @@ -60,6 +81,7 @@ struct mm_walk {
const struct mm_walk_ops *ops;
struct mm_struct *mm;
struct vm_area_struct *vma;
enum page_walk_action action;
void *private;
};

Expand Down
58 changes: 32 additions & 26 deletions mm/hmm.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -474,23 +474,32 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
{
struct hmm_vma_walk *hmm_vma_walk = walk->private;
struct hmm_range *range = hmm_vma_walk->range;
unsigned long addr = start, next;
pmd_t *pmdp;
unsigned long addr = start;
pud_t pud;
int ret;
int ret = 0;
spinlock_t *ptl = pud_trans_huge_lock(pudp, walk->vma);

if (!ptl)
return 0;

/* Normally we don't want to split the huge page */
walk->action = ACTION_CONTINUE;

again:
pud = READ_ONCE(*pudp);
if (pud_none(pud))
return hmm_vma_walk_hole(start, end, walk);
if (pud_none(pud)) {
ret = hmm_vma_walk_hole(start, end, walk);
goto out_unlock;
}

if (pud_huge(pud) && pud_devmap(pud)) {
unsigned long i, npages, pfn;
uint64_t *pfns, cpu_flags;
bool fault, write_fault;

if (!pud_present(pud))
return hmm_vma_walk_hole(start, end, walk);
if (!pud_present(pud)) {
ret = hmm_vma_walk_hole(start, end, walk);
goto out_unlock;
}

i = (addr - range->start) >> PAGE_SHIFT;
npages = (end - addr) >> PAGE_SHIFT;
Expand All @@ -499,16 +508,20 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
cpu_flags = pud_to_hmm_pfn_flags(range, pud);
hmm_range_need_fault(hmm_vma_walk, pfns, npages,
cpu_flags, &fault, &write_fault);
if (fault || write_fault)
return hmm_vma_walk_hole_(addr, end, fault,
write_fault, walk);
if (fault || write_fault) {
ret = hmm_vma_walk_hole_(addr, end, fault,
write_fault, walk);
goto out_unlock;
}

pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
for (i = 0; i < npages; ++i, ++pfn) {
hmm_vma_walk->pgmap = get_dev_pagemap(pfn,
hmm_vma_walk->pgmap);
if (unlikely(!hmm_vma_walk->pgmap))
return -EBUSY;
if (unlikely(!hmm_vma_walk->pgmap)) {
ret = -EBUSY;
goto out_unlock;
}
pfns[i] = hmm_device_entry_from_pfn(range, pfn) |
cpu_flags;
}
Expand All @@ -517,22 +530,15 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
hmm_vma_walk->pgmap = NULL;
}
hmm_vma_walk->last = end;
return 0;
goto out_unlock;
}

split_huge_pud(walk->vma, pudp, addr);
if (pud_none(*pudp))
goto again;
/* Ask for the PUD to be split */
walk->action = ACTION_SUBTREE;

pmdp = pmd_offset(pudp, addr);
do {
next = pmd_addr_end(addr, end);
ret = hmm_vma_walk_pmd(pmdp, addr, next, walk);
if (ret)
return ret;
} while (pmdp++, addr = next, addr != end);

return 0;
out_unlock:
spin_unlock(ptl);
return ret;
}
#else
#define hmm_vma_walk_pud NULL
Expand Down
50 changes: 35 additions & 15 deletions mm/pagewalk.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -46,6 +46,9 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
break;
continue;
}

walk->action = ACTION_SUBTREE;

/*
* This implies that each ->pmd_entry() handler
* needs to know about pmd_trans_huge() pmds
Expand All @@ -55,16 +58,21 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
if (err)
break;

if (walk->action == ACTION_AGAIN)
goto again;

/*
* Check this here so we only break down trans_huge
* pages when we _need_ to
*/
if (!ops->pte_entry)
if (walk->action == ACTION_CONTINUE ||
!(ops->pte_entry))
continue;

split_huge_pmd(walk->vma, pmd, addr);
if (pmd_trans_unstable(pmd))
goto again;

err = walk_pte_range(pmd, addr, next, walk);
if (err)
break;
Expand Down Expand Up @@ -93,24 +101,25 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
continue;
}

if (ops->pud_entry) {
spinlock_t *ptl = pud_trans_huge_lock(pud, walk->vma);
walk->action = ACTION_SUBTREE;

if (ptl) {
err = ops->pud_entry(pud, addr, next, walk);
spin_unlock(ptl);
if (err)
break;
continue;
}
}
if (ops->pud_entry)
err = ops->pud_entry(pud, addr, next, walk);
if (err)
break;

if (walk->action == ACTION_AGAIN)
goto again;

if (walk->action == ACTION_CONTINUE ||
!(ops->pmd_entry || ops->pte_entry))
continue;

split_huge_pud(walk->vma, pud, addr);
if (pud_none(*pud))
goto again;

if (ops->pmd_entry || ops->pte_entry)
err = walk_pmd_range(pud, addr, next, walk);
err = walk_pmd_range(pud, addr, next, walk);
if (err)
break;
} while (pud++, addr = next, addr != end);
Expand All @@ -136,7 +145,12 @@ static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,
break;
continue;
}
if (ops->pmd_entry || ops->pte_entry)
if (ops->p4d_entry) {
err = ops->p4d_entry(p4d, addr, next, walk);
if (err)
break;
}
if (ops->pud_entry || ops->pmd_entry || ops->pte_entry)
err = walk_pud_range(p4d, addr, next, walk);
if (err)
break;
Expand All @@ -163,7 +177,13 @@ static int walk_pgd_range(unsigned long addr, unsigned long end,
break;
continue;
}
if (ops->pmd_entry || ops->pte_entry)
if (ops->pgd_entry) {
err = ops->pgd_entry(pgd, addr, next, walk);
if (err)
break;
}
if (ops->p4d_entry || ops->pud_entry || ops->pmd_entry ||
ops->pte_entry)
err = walk_p4d_range(pgd, addr, next, walk);
if (err)
break;
Expand Down

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