Balbir Singh
2025-Mar-06 04:42 UTC
[RFC 05/11] mm/memory/fault: Add support for zone device THP fault handling
When the CPU touches a zone device THP entry, the data needs to
be migrated back to the CPU, call migrate_to_ram() on these pages
via do_huge_pmd_device_private() fault handling helper.
Signed-off-by: Balbir Singh <balbirs at nvidia.com>
---
include/linux/huge_mm.h | 7 +++++++
mm/huge_memory.c | 35 +++++++++++++++++++++++++++++++++++
mm/memory.c | 6 ++++--
3 files changed, 46 insertions(+), 2 deletions(-)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index e893d546a49f..ad0c0ccfcbc2 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -479,6 +479,8 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma,
unsigned long addr,
vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf);
+vm_fault_t do_huge_pmd_device_private(struct vm_fault *vmf);
+
extern struct folio *huge_zero_folio;
extern unsigned long huge_zero_pfn;
@@ -634,6 +636,11 @@ static inline vm_fault_t do_huge_pmd_numa_page(struct
vm_fault *vmf)
return 0;
}
+static inline vm_fault_t do_huge_pmd_device_private(struct vm_fault *vmf)
+{
+ return 0;
+}
+
static inline bool is_huge_zero_folio(const struct folio *folio)
{
return false;
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index d8e018d1bdbd..995ac8be5709 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1375,6 +1375,41 @@ vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault
*vmf)
return __do_huge_pmd_anonymous_page(vmf);
}
+vm_fault_t do_huge_pmd_device_private(struct vm_fault *vmf)
+{
+ struct vm_area_struct *vma = vmf->vma;
+ unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
+ vm_fault_t ret;
+ spinlock_t *ptl;
+ swp_entry_t swp_entry;
+ struct page *page;
+
+ if (!thp_vma_suitable_order(vma, haddr, PMD_ORDER))
+ return VM_FAULT_FALLBACK;
+
+ if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
+ vma_end_read(vma);
+ return VM_FAULT_RETRY;
+ }
+
+ ptl = pmd_lock(vma->vm_mm, vmf->pmd);
+ if (unlikely(!pmd_same(*vmf->pmd, vmf->orig_pmd))) {
+ spin_unlock(ptl);
+ return 0;
+ }
+
+ swp_entry = pmd_to_swp_entry(vmf->orig_pmd);
+ page = pfn_swap_entry_to_page(swp_entry);
+ vmf->page = page;
+ vmf->pte = NULL;
+ get_page(page);
+ spin_unlock(ptl);
+ ret = page_pgmap(page)->ops->migrate_to_ram(vmf);
+ put_page(page);
+
+ return ret;
+}
+
static int insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
pmd_t *pmd, pfn_t pfn, pgprot_t prot, bool write,
pgtable_t pgtable)
diff --git a/mm/memory.c b/mm/memory.c
index a838c8c44bfd..deaa67b88708 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -6149,8 +6149,10 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct
*vma,
vmf.orig_pmd = pmdp_get_lockless(vmf.pmd);
if (unlikely(is_swap_pmd(vmf.orig_pmd))) {
- VM_BUG_ON(thp_migration_supported() &&
- !is_pmd_migration_entry(vmf.orig_pmd));
+ if (is_device_private_entry(
+ pmd_to_swp_entry(vmf.orig_pmd)))
+ return do_huge_pmd_device_private(&vmf);
+
if (is_pmd_migration_entry(vmf.orig_pmd))
pmd_migration_entry_wait(mm, vmf.pmd);
return 0;
--
2.48.1
David Hildenbrand
2025-Jul-08 14:40 UTC
[RFC 05/11] mm/memory/fault: Add support for zone device THP fault handling
On 06.03.25 05:42, Balbir Singh wrote:> When the CPU touches a zone device THP entry, the data needs to > be migrated back to the CPU, call migrate_to_ram() on these pages > via do_huge_pmd_device_private() fault handling helper. > > Signed-off-by: Balbir Singh <balbirs at nvidia.com> > --- > include/linux/huge_mm.h | 7 +++++++ > mm/huge_memory.c | 35 +++++++++++++++++++++++++++++++++++ > mm/memory.c | 6 ++++-- > 3 files changed, 46 insertions(+), 2 deletions(-) > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index e893d546a49f..ad0c0ccfcbc2 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -479,6 +479,8 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr, > > vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf); > > +vm_fault_t do_huge_pmd_device_private(struct vm_fault *vmf); > + > extern struct folio *huge_zero_folio; > extern unsigned long huge_zero_pfn; > > @@ -634,6 +636,11 @@ static inline vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf) > return 0; > } > > +static inline vm_fault_t do_huge_pmd_device_private(struct vm_fault *vmf) > +{ > + return 0; > +} > + > static inline bool is_huge_zero_folio(const struct folio *folio) > { > return false; > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index d8e018d1bdbd..995ac8be5709 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1375,6 +1375,41 @@ vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf) > return __do_huge_pmd_anonymous_page(vmf); > } > > +vm_fault_t do_huge_pmd_device_private(struct vm_fault *vmf) > +{ > + struct vm_area_struct *vma = vmf->vma; > + unsigned long haddr = vmf->address & HPAGE_PMD_MASK; > + vm_fault_t ret; > + spinlock_t *ptl; > + swp_entry_t swp_entry; > + struct page *page; > + > + if (!thp_vma_suitable_order(vma, haddr, PMD_ORDER)) > + return VM_FAULT_FALLBACK;I'm confused. Why is that required when we already have a PMD entry? Apart from that, nothing jumped at me. -- Cheers, David / dhildenb