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Date: Mon, 4 Apr 2022 21:48:33 -0400
From: Peter Xu <peterx@...hat.com>
To: linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc: Mike Kravetz <mike.kravetz@...cle.com>,
Nadav Amit <nadav.amit@...il.com>,
Matthew Wilcox <willy@...radead.org>,
Mike Rapoport <rppt@...ux.vnet.ibm.com>,
David Hildenbrand <david@...hat.com>,
Hugh Dickins <hughd@...gle.com>,
Jerome Glisse <jglisse@...hat.com>,
"Kirill A . Shutemov" <kirill@...temov.name>,
Andrea Arcangeli <aarcange@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Axel Rasmussen <axelrasmussen@...gle.com>,
Alistair Popple <apopple@...dia.com>, peterx@...hat.com
Subject: [PATCH v8 02/23] mm: Teach core mm about pte markers
This patch still does not use pte marker in any way, however it teaches the
core mm about the pte marker idea.
For example, handle_pte_marker() is introduced that will parse and handle all
the pte marker faults.
Many of the places are more about commenting it up - so that we know there's
the possibility of pte marker showing up, and why we don't need special code
for the cases.
Signed-off-by: Peter Xu <peterx@...hat.com>
---
fs/userfaultfd.c | 10 ++++++----
mm/filemap.c | 5 +++++
mm/hmm.c | 2 +-
mm/memcontrol.c | 8 ++++++--
mm/memory.c | 23 +++++++++++++++++++++++
mm/mincore.c | 3 ++-
mm/mprotect.c | 3 +++
7 files changed, 46 insertions(+), 8 deletions(-)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index aa0c47cb0d16..8b4a94f5a238 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -249,9 +249,10 @@ static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
/*
* Lockless access: we're in a wait_event so it's ok if it
- * changes under us.
+ * changes under us. PTE markers should be handled the same as none
+ * ptes here.
*/
- if (huge_pte_none(pte))
+ if (huge_pte_none_mostly(pte))
ret = true;
if (!huge_pte_write(pte) && (reason & VM_UFFD_WP))
ret = true;
@@ -330,9 +331,10 @@ static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
pte = pte_offset_map(pmd, address);
/*
* Lockless access: we're in a wait_event so it's ok if it
- * changes under us.
+ * changes under us. PTE markers should be handled the same as none
+ * ptes here.
*/
- if (pte_none(*pte))
+ if (pte_none_mostly(*pte))
ret = true;
if (!pte_write(*pte) && (reason & VM_UFFD_WP))
ret = true;
diff --git a/mm/filemap.c b/mm/filemap.c
index 3a5ffb5587cd..ef77dae8c28d 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3382,6 +3382,11 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
vmf->pte += xas.xa_index - last_pgoff;
last_pgoff = xas.xa_index;
+ /*
+ * NOTE: If there're PTE markers, we'll leave them to be
+ * handled in the specific fault path, and it'll prohibit the
+ * fault-around logic.
+ */
if (!pte_none(*vmf->pte))
goto unlock;
diff --git a/mm/hmm.c b/mm/hmm.c
index af71aac3140e..3fd3242c5e50 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -239,7 +239,7 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
pte_t pte = *ptep;
uint64_t pfn_req_flags = *hmm_pfn;
- if (pte_none(pte)) {
+ if (pte_none_mostly(pte)) {
required_fault =
hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0);
if (required_fault)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7a08737bac4b..08af97c73f0f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5644,10 +5644,14 @@ static enum mc_target_type get_mctgt_type(struct vm_area_struct *vma,
if (pte_present(ptent))
page = mc_handle_present_pte(vma, addr, ptent);
+ else if (pte_none_mostly(ptent))
+ /*
+ * PTE markers should be treated as a none pte here, separated
+ * from other swap handling below.
+ */
+ page = mc_handle_file_pte(vma, addr, ptent);
else if (is_swap_pte(ptent))
page = mc_handle_swap_pte(vma, ptent, &ent);
- else if (pte_none(ptent))
- page = mc_handle_file_pte(vma, addr, ptent);
if (!page && !ent.val)
return ret;
diff --git a/mm/memory.c b/mm/memory.c
index 2c5d1bb4694f..3f396241a7db 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -100,6 +100,8 @@ struct page *mem_map;
EXPORT_SYMBOL(mem_map);
#endif
+static vm_fault_t do_fault(struct vm_fault *vmf);
+
/*
* A number of key systems in x86 including ioremap() rely on the assumption
* that high_memory defines the upper bound on direct map memory, then end
@@ -1415,6 +1417,8 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
if (!should_zap_page(details, page))
continue;
rss[mm_counter(page)]--;
+ } else if (is_pte_marker_entry(entry)) {
+ /* By default, simply drop all pte markers when zap */
} else if (is_hwpoison_entry(entry)) {
if (!should_zap_cows(details))
continue;
@@ -3555,6 +3559,23 @@ static inline bool should_try_to_free_swap(struct page *page,
page_count(page) == 2;
}
+static vm_fault_t handle_pte_marker(struct vm_fault *vmf)
+{
+ swp_entry_t entry = pte_to_swp_entry(vmf->orig_pte);
+ unsigned long marker = pte_marker_get(entry);
+
+ /*
+ * PTE markers should always be with file-backed memories, and the
+ * marker should never be empty. If anything weird happened, the best
+ * thing to do is to kill the process along with its mm.
+ */
+ if (WARN_ON_ONCE(vma_is_anonymous(vmf->vma) || !marker))
+ return VM_FAULT_SIGBUS;
+
+ /* TODO: handle pte markers */
+ return 0;
+}
+
/*
* We enter with non-exclusive mmap_lock (to exclude vma changes,
* but allow concurrent faults), and pte mapped but not yet locked.
@@ -3592,6 +3613,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
ret = vmf->page->pgmap->ops->migrate_to_ram(vmf);
} else if (is_hwpoison_entry(entry)) {
ret = VM_FAULT_HWPOISON;
+ } else if (is_pte_marker_entry(entry)) {
+ ret = handle_pte_marker(vmf);
} else {
print_bad_pte(vma, vmf->address, vmf->orig_pte, NULL);
ret = VM_FAULT_SIGBUS;
diff --git a/mm/mincore.c b/mm/mincore.c
index f4f627325e12..fa200c14185f 100644
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -122,7 +122,8 @@ static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
for (; addr != end; ptep++, addr += PAGE_SIZE) {
pte_t pte = *ptep;
- if (pte_none(pte))
+ /* We need to do cache lookup too for pte markers */
+ if (pte_none_mostly(pte))
__mincore_unmapped_range(addr, addr + PAGE_SIZE,
vma, vec);
else if (pte_present(pte))
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 56060acdabd3..709a6f73b764 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -188,6 +188,9 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
newpte = pte_swp_mksoft_dirty(newpte);
if (pte_swp_uffd_wp(oldpte))
newpte = pte_swp_mkuffd_wp(newpte);
+ } else if (is_pte_marker_entry(entry)) {
+ /* Skip it, the same as none pte */
+ continue;
} else {
newpte = oldpte;
}
--
2.32.0
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