| Message ID | 20190722154210.42799-12-steven.price@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Generic page walk and ptdump | expand |
On Mon, Jul 22, 2019 at 04:42:00PM +0100, Steven Price wrote: > pgd_entry() and pud_entry() were removed by commit 0b1fbfe50006c410 > ("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 a00cc7d9dd93d66a ("mm, x86: add support for > PUD-sized transparent hugepages") already re-added pud_entry() but with > different semantics to the other callbacks. Since there have never > been upstream users of this, revert the semantics back to match the > other callbacks. This means pud_entry() is called for all entries, not > just transparent huge pages. > > Signed-off-by: Steven Price <steven.price@arm.com> > --- > include/linux/mm.h | 15 +++++++++------ > mm/pagewalk.c | 27 ++++++++++++++++----------- > 2 files changed, 25 insertions(+), 17 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 0334ca97c584..b22799129128 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1432,15 +1432,14 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma, > > /** > * mm_walk - 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 How are these expected to work with folding? For example, on arm64 with 64K pages and 42-bit VA, you can have 2-level tables where the PGD is P4D, PUD, and PMD. IIUC we'd invoke the callbacks for each of those levels where we found an entry in the pgd. Either the callee handle that, or we should inhibit the callbacks when levels are folded, and I think that needs to be explcitly stated either way. IIRC on x86 the p4d folding is dynamic depending on whether the HW supports 5-level page tables. Maybe that implies the callee has to handle that. Thanks, Mark. > * 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 > @@ -1455,6 +1454,10 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma, > * (see the comment on walk_page_range() for more details) > */ > struct mm_walk { > + 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, > diff --git a/mm/pagewalk.c b/mm/pagewalk.c > index c3084ff2569d..98373a9f88b8 100644 > --- a/mm/pagewalk.c > +++ b/mm/pagewalk.c > @@ -90,15 +90,9 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end, > } > > if (walk->pud_entry) { > - spinlock_t *ptl = pud_trans_huge_lock(pud, walk->vma); > - > - if (ptl) { > - err = walk->pud_entry(pud, addr, next, walk); > - spin_unlock(ptl); > - if (err) > - break; > - continue; > - } > + err = walk->pud_entry(pud, addr, next, walk); > + if (err) > + break; > } > > split_huge_pud(walk->vma, pud, addr); > @@ -131,7 +125,12 @@ static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end, > break; > continue; > } > - if (walk->pmd_entry || walk->pte_entry) > + if (walk->p4d_entry) { > + err = walk->p4d_entry(p4d, addr, next, walk); > + if (err) > + break; > + } > + if (walk->pud_entry || walk->pmd_entry || walk->pte_entry) > err = walk_pud_range(p4d, addr, next, walk); > if (err) > break; > @@ -157,7 +156,13 @@ static int walk_pgd_range(unsigned long addr, unsigned long end, > break; > continue; > } > - if (walk->pmd_entry || walk->pte_entry) > + if (walk->pgd_entry) { > + err = walk->pgd_entry(pgd, addr, next, walk); > + if (err) > + break; > + } > + if (walk->p4d_entry || walk->pud_entry || walk->pmd_entry || > + walk->pte_entry) > err = walk_p4d_range(pgd, addr, next, walk); > if (err) > break; > -- > 2.20.1 >
On 23/07/2019 11:14, Mark Rutland wrote: > On Mon, Jul 22, 2019 at 04:42:00PM +0100, Steven Price wrote: >> pgd_entry() and pud_entry() were removed by commit 0b1fbfe50006c410 >> ("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 a00cc7d9dd93d66a ("mm, x86: add support for >> PUD-sized transparent hugepages") already re-added pud_entry() but with >> different semantics to the other callbacks. Since there have never >> been upstream users of this, revert the semantics back to match the >> other callbacks. This means pud_entry() is called for all entries, not >> just transparent huge pages. >> >> Signed-off-by: Steven Price <steven.price@arm.com> >> --- >> include/linux/mm.h | 15 +++++++++------ >> mm/pagewalk.c | 27 ++++++++++++++++----------- >> 2 files changed, 25 insertions(+), 17 deletions(-) >> >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index 0334ca97c584..b22799129128 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -1432,15 +1432,14 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma, >> >> /** >> * mm_walk - 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 > > How are these expected to work with folding? > > For example, on arm64 with 64K pages and 42-bit VA, you can have 2-level > tables where the PGD is P4D, PUD, and PMD. IIUC we'd invoke the > callbacks for each of those levels where we found an entry in the pgd. > > Either the callee handle that, or we should inhibit the callbacks when > levels are folded, and I think that needs to be explcitly stated either > way. > > IIRC on x86 the p4d folding is dynamic depending on whether the HW > supports 5-level page tables. Maybe that implies the callee has to > handle that. Yes, my assumption is that it has to be up to the callee to handle that because folding can be dynamic. I believe this also was how these callbacks work before they were removed. However I'll add a comment explaining that here as it's probably non-obvious. Steve
On Wed, Jul 24, 2019 at 02:53:04PM +0100, Steven Price wrote: > On 23/07/2019 11:14, Mark Rutland wrote: > > On Mon, Jul 22, 2019 at 04:42:00PM +0100, Steven Price wrote: > >> pgd_entry() and pud_entry() were removed by commit 0b1fbfe50006c410 > >> ("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 a00cc7d9dd93d66a ("mm, x86: add support for > >> PUD-sized transparent hugepages") already re-added pud_entry() but with > >> different semantics to the other callbacks. Since there have never > >> been upstream users of this, revert the semantics back to match the > >> other callbacks. This means pud_entry() is called for all entries, not > >> just transparent huge pages. > >> > >> Signed-off-by: Steven Price <steven.price@arm.com> > >> --- > >> include/linux/mm.h | 15 +++++++++------ > >> mm/pagewalk.c | 27 ++++++++++++++++----------- > >> 2 files changed, 25 insertions(+), 17 deletions(-) > >> > >> diff --git a/include/linux/mm.h b/include/linux/mm.h > >> index 0334ca97c584..b22799129128 100644 > >> --- a/include/linux/mm.h > >> +++ b/include/linux/mm.h > >> @@ -1432,15 +1432,14 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma, > >> > >> /** > >> * mm_walk - 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 > > > > How are these expected to work with folding? > > > > For example, on arm64 with 64K pages and 42-bit VA, you can have 2-level > > tables where the PGD is P4D, PUD, and PMD. IIUC we'd invoke the > > callbacks for each of those levels where we found an entry in the pgd. > > > > Either the callee handle that, or we should inhibit the callbacks when > > levels are folded, and I think that needs to be explcitly stated either > > way. > > > > IIRC on x86 the p4d folding is dynamic depending on whether the HW > > supports 5-level page tables. Maybe that implies the callee has to > > handle that. > > Yes, my assumption is that it has to be up to the callee to handle that > because folding can be dynamic. I believe this also was how these > callbacks work before they were removed. However I'll add a comment > explaining that here as it's probably non-obvious. That sounds good to me. Thanks, Mark.
On 07/22/2019 09:12 PM, Steven Price wrote: > pgd_entry() and pud_entry() were removed by commit 0b1fbfe50006c410 > ("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 a00cc7d9dd93d66a ("mm, x86: add support for > PUD-sized transparent hugepages") already re-added pud_entry() but with > different semantics to the other callbacks. Since there have never > been upstream users of this, revert the semantics back to match the > other callbacks. This means pud_entry() is called for all entries, not > just transparent huge pages. > > Signed-off-by: Steven Price <steven.price@arm.com> > --- > include/linux/mm.h | 15 +++++++++------ > mm/pagewalk.c | 27 ++++++++++++++++----------- > 2 files changed, 25 insertions(+), 17 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 0334ca97c584..b22799129128 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1432,15 +1432,14 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma, > > /** > * mm_walk - 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 > @@ -1455,6 +1454,10 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma, > * (see the comment on walk_page_range() for more details) > */ > struct mm_walk { > + 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, > diff --git a/mm/pagewalk.c b/mm/pagewalk.c > index c3084ff2569d..98373a9f88b8 100644 > --- a/mm/pagewalk.c > +++ b/mm/pagewalk.c > @@ -90,15 +90,9 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end, > } > > if (walk->pud_entry) { > - spinlock_t *ptl = pud_trans_huge_lock(pud, walk->vma); > - > - if (ptl) { > - err = walk->pud_entry(pud, addr, next, walk); > - spin_unlock(ptl); > - if (err) > - break; > - continue; > - } > + err = walk->pud_entry(pud, addr, next, walk); > + if (err) > + break; But will not this still encounter possible THP entries when walking user page tables (valid walk->vma) in which case still needs to get a lock. OR will the callback take care of it ?
On 28/07/2019 13:33, Anshuman Khandual wrote: > > > On 07/22/2019 09:12 PM, Steven Price wrote: >> pgd_entry() and pud_entry() were removed by commit 0b1fbfe50006c410 >> ("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 a00cc7d9dd93d66a ("mm, x86: add support for >> PUD-sized transparent hugepages") already re-added pud_entry() but with >> different semantics to the other callbacks. Since there have never >> been upstream users of this, revert the semantics back to match the >> other callbacks. This means pud_entry() is called for all entries, not >> just transparent huge pages. >> >> Signed-off-by: Steven Price <steven.price@arm.com> >> --- >> include/linux/mm.h | 15 +++++++++------ >> mm/pagewalk.c | 27 ++++++++++++++++----------- >> 2 files changed, 25 insertions(+), 17 deletions(-) >> >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index 0334ca97c584..b22799129128 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -1432,15 +1432,14 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma, >> >> /** >> * mm_walk - 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 >> @@ -1455,6 +1454,10 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma, >> * (see the comment on walk_page_range() for more details) >> */ >> struct mm_walk { >> + 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, >> diff --git a/mm/pagewalk.c b/mm/pagewalk.c >> index c3084ff2569d..98373a9f88b8 100644 >> --- a/mm/pagewalk.c >> +++ b/mm/pagewalk.c >> @@ -90,15 +90,9 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end, >> } >> >> if (walk->pud_entry) { >> - spinlock_t *ptl = pud_trans_huge_lock(pud, walk->vma); >> - >> - if (ptl) { >> - err = walk->pud_entry(pud, addr, next, walk); >> - spin_unlock(ptl); >> - if (err) >> - break; >> - continue; >> - } >> + err = walk->pud_entry(pud, addr, next, walk); >> + if (err) >> + break; > > But will not this still encounter possible THP entries when walking user > page tables (valid walk->vma) in which case still needs to get a lock. > OR will the callback take care of it ? This is what I mean in the commit message by: > Since there have never > been upstream users of this, revert the semantics back to match the > other callbacks. This means pud_entry() is called for all entries, not > just transparent huge pages. So the expectation is that the caller takes care of it. However, having checked again, it appears that mm/hmm.c now does use this callback (merged in v5.2-rc1). Jérôme - are you happy with this change in semantics? It looks like hmm_vma_walk_pud() should deal gracefully with both normal and large pages - although I'm unsure whether you are relying on the lock from pud_trans_huge_lock()? Thanks, Steve
diff --git a/include/linux/mm.h b/include/linux/mm.h index 0334ca97c584..b22799129128 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1432,15 +1432,14 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma, /** * mm_walk - 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 @@ -1455,6 +1454,10 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma, * (see the comment on walk_page_range() for more details) */ struct mm_walk { + 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, diff --git a/mm/pagewalk.c b/mm/pagewalk.c index c3084ff2569d..98373a9f88b8 100644 --- a/mm/pagewalk.c +++ b/mm/pagewalk.c @@ -90,15 +90,9 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end, } if (walk->pud_entry) { - spinlock_t *ptl = pud_trans_huge_lock(pud, walk->vma); - - if (ptl) { - err = walk->pud_entry(pud, addr, next, walk); - spin_unlock(ptl); - if (err) - break; - continue; - } + err = walk->pud_entry(pud, addr, next, walk); + if (err) + break; } split_huge_pud(walk->vma, pud, addr); @@ -131,7 +125,12 @@ static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end, break; continue; } - if (walk->pmd_entry || walk->pte_entry) + if (walk->p4d_entry) { + err = walk->p4d_entry(p4d, addr, next, walk); + if (err) + break; + } + if (walk->pud_entry || walk->pmd_entry || walk->pte_entry) err = walk_pud_range(p4d, addr, next, walk); if (err) break; @@ -157,7 +156,13 @@ static int walk_pgd_range(unsigned long addr, unsigned long end, break; continue; } - if (walk->pmd_entry || walk->pte_entry) + if (walk->pgd_entry) { + err = walk->pgd_entry(pgd, addr, next, walk); + if (err) + break; + } + if (walk->p4d_entry || walk->pud_entry || walk->pmd_entry || + walk->pte_entry) err = walk_p4d_range(pgd, addr, next, walk); if (err) break;
pgd_entry() and pud_entry() were removed by commit 0b1fbfe50006c410 ("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 a00cc7d9dd93d66a ("mm, x86: add support for PUD-sized transparent hugepages") already re-added pud_entry() but with different semantics to the other callbacks. Since there have never been upstream users of this, revert the semantics back to match the other callbacks. This means pud_entry() is called for all entries, not just transparent huge pages. Signed-off-by: Steven Price <steven.price@arm.com> --- include/linux/mm.h | 15 +++++++++------ mm/pagewalk.c | 27 ++++++++++++++++----------- 2 files changed, 25 insertions(+), 17 deletions(-)