lkml.org 
[lkml]   [2019]   [Jul]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH v9 12/21] mm: pagewalk: Allow walking without vma
    From
    Date


    On 07/22/2019 09:12 PM, Steven Price wrote:
    > Since 48684a65b4e3: "mm: pagewalk: fix misbehavior of walk_page_range
    > for vma(VM_PFNMAP)", page_table_walk() will report any kernel area as
    > a hole, because it lacks a vma.
    >
    > This means each arch has re-implemented page table walking when needed,
    > for example in the per-arch ptdump walker.
    >
    > Remove the requirement to have a vma except when trying to split huge
    > pages.
    >
    > Signed-off-by: Steven Price <steven.price@arm.com>
    > ---
    > mm/pagewalk.c | 25 +++++++++++++++++--------
    > 1 file changed, 17 insertions(+), 8 deletions(-)
    >
    > diff --git a/mm/pagewalk.c b/mm/pagewalk.c
    > index 98373a9f88b8..1cbef99e9258 100644
    > --- a/mm/pagewalk.c
    > +++ b/mm/pagewalk.c
    > @@ -36,7 +36,7 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
    > do {
    > again:
    > next = pmd_addr_end(addr, end);
    > - if (pmd_none(*pmd) || !walk->vma) {
    > + if (pmd_none(*pmd)) {
    > if (walk->pte_hole)
    > err = walk->pte_hole(addr, next, walk);
    > if (err)
    > @@ -59,9 +59,14 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
    > if (!walk->pte_entry)
    > continue;
    >
    > - split_huge_pmd(walk->vma, pmd, addr);
    > - if (pmd_trans_unstable(pmd))
    > - goto again;
    > + if (walk->vma) {
    > + split_huge_pmd(walk->vma, pmd, addr);

    Check for a PMD THP entry before attempting to split it ?

    > + if (pmd_trans_unstable(pmd))
    > + goto again;
    > + } else if (pmd_leaf(*pmd)) {
    > + continue;
    > + }
    > +
    > err = walk_pte_range(pmd, addr, next, walk);
    > if (err)
    > break;
    > @@ -81,7 +86,7 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
    > do {
    > again:
    > next = pud_addr_end(addr, end);
    > - if (pud_none(*pud) || !walk->vma) {
    > + if (pud_none(*pud)) {
    > if (walk->pte_hole)
    > err = walk->pte_hole(addr, next, walk);
    > if (err)
    > @@ -95,9 +100,13 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
    > break;
    > }
    >
    > - split_huge_pud(walk->vma, pud, addr);
    > - if (pud_none(*pud))
    > - goto again;
    > + if (walk->vma) {
    > + split_huge_pud(walk->vma, pud, addr);

    Check for a PUD THP entry before attempting to split it ?

    > + if (pud_none(*pud))
    > + goto again;
    > + } else if (pud_leaf(*pud)) {
    > + continue;
    > + }

    This is bit cryptic. walk->vma check should be inside a helper is_user_page_table()
    or similar to make things clear. p4d_leaf() check missing in walk_p4d_range() for
    kernel page table walk ? Wondering if p?d_leaf() test should be moved earlier while
    calling p?d_entry() for kernel page table walk.

    \
     
     \ /
      Last update: 2019-07-28 16:20    [W:3.125 / U:0.144 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site