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Message-ID: <20250820010415.699353-14-anthony.yznaga@oracle.com>
Date: Tue, 19 Aug 2025 18:04:06 -0700
From: Anthony Yznaga <anthony.yznaga@...cle.com>
To: linux-mm@...ck.org
Cc: akpm@...ux-foundation.org, andreyknvl@...il.com, arnd@...db.de,
bp@...en8.de, brauner@...nel.org, bsegall@...gle.com, corbet@....net,
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Subject: [PATCH v3 13/22] mm/mshare: prepare for page table sharing support
From: Khalid Aziz <khalid@...nel.org>
In preparation for enabling the handling of page faults in an mshare
region provide a way to link an mshare shared page table to a process
page table and otherwise find the actual vma in order to handle a page
fault. Implement an unmap_page_range vm_ops function for msharefs VMAs
to unlink shared page tables when a process exits or an mshare region
is explicitly unmapped.
Signed-off-by: Khalid Aziz <khalid@...nel.org>
Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Signed-off-by: Anthony Yznaga <anthony.yznaga@...cle.com>
---
include/linux/mm.h | 6 +++
mm/memory.c | 6 +++
mm/mshare.c | 107 +++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 119 insertions(+)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index c8dfa5c6e7d4..3a8dddb5925a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1009,11 +1009,17 @@ static inline bool vma_is_anon_shmem(struct vm_area_struct *vma) { return false;
int vma_is_stack_for_current(struct vm_area_struct *vma);
#ifdef CONFIG_MSHARE
+vm_fault_t find_shared_vma(struct vm_area_struct **vma, unsigned long *addrp);
static inline bool vma_is_mshare(const struct vm_area_struct *vma)
{
return vma->vm_flags & VM_MSHARE;
}
#else
+static inline vm_fault_t find_shared_vma(struct vm_area_struct **vma, unsigned long *addrp)
+{
+ WARN_ON_ONCE(1);
+ return VM_FAULT_SIGBUS;
+}
static inline bool vma_is_mshare(const struct vm_area_struct *vma)
{
return false;
diff --git a/mm/memory.c b/mm/memory.c
index 4e3bb49b95e2..177eb53475cb 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -6475,6 +6475,12 @@ vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
if (ret)
goto out;
+ if (unlikely(vma_is_mshare(vma))) {
+ WARN_ON_ONCE(1);
+ ret = VM_FAULT_SIGBUS;
+ goto out;
+ }
+
if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
flags & FAULT_FLAG_INSTRUCTION,
flags & FAULT_FLAG_REMOTE)) {
diff --git a/mm/mshare.c b/mm/mshare.c
index be7cae739225..f7b7904f0405 100644
--- a/mm/mshare.c
+++ b/mm/mshare.c
@@ -21,6 +21,8 @@
#include <linux/falloc.h>
#include <asm/tlbflush.h>
+#include <asm/tlb.h>
+
const unsigned long mshare_align = P4D_SIZE;
const unsigned long mshare_base = mshare_align;
@@ -50,6 +52,66 @@ static const struct mmu_notifier_ops mshare_mmu_ops = {
.arch_invalidate_secondary_tlbs = mshare_invalidate_tlbs,
};
+static p4d_t *walk_to_p4d(struct mm_struct *mm, unsigned long addr)
+{
+ pgd_t *pgd;
+ p4d_t *p4d;
+
+ pgd = pgd_offset(mm, addr);
+ p4d = p4d_alloc(mm, pgd, addr);
+ if (!p4d)
+ return NULL;
+
+ return p4d;
+}
+
+/* Returns holding the host mm's lock for read. Caller must release. */
+vm_fault_t
+find_shared_vma(struct vm_area_struct **vmap, unsigned long *addrp)
+{
+ struct vm_area_struct *vma, *guest = *vmap;
+ struct mshare_data *m_data = guest->vm_private_data;
+ struct mm_struct *host_mm = m_data->mm;
+ unsigned long host_addr;
+ p4d_t *p4d, *guest_p4d;
+
+ mmap_read_lock_nested(host_mm, SINGLE_DEPTH_NESTING);
+ host_addr = *addrp - guest->vm_start + host_mm->mmap_base;
+ p4d = walk_to_p4d(host_mm, host_addr);
+ guest_p4d = walk_to_p4d(guest->vm_mm, *addrp);
+ if (!p4d_same(*guest_p4d, *p4d)) {
+ spinlock_t *guest_ptl = &guest->vm_mm->page_table_lock;
+
+ spin_lock(guest_ptl);
+ if (!p4d_same(*guest_p4d, *p4d)) {
+ pud_t *pud = p4d_pgtable(*p4d);
+
+ ptdesc_pud_pts_inc(virt_to_ptdesc(pud));
+ set_p4d(guest_p4d, *p4d);
+ spin_unlock(guest_ptl);
+ mmap_read_unlock(host_mm);
+ return VM_FAULT_NOPAGE;
+ }
+ spin_unlock(guest_ptl);
+ }
+
+ *addrp = host_addr;
+ vma = find_vma(host_mm, host_addr);
+
+ /* XXX: expand stack? */
+ if (vma && vma->vm_start > host_addr)
+ vma = NULL;
+
+ *vmap = vma;
+
+ /*
+ * release host mm lock unless a matching vma is found
+ */
+ if (!vma)
+ mmap_read_unlock(host_mm);
+ return 0;
+}
+
static int mshare_vm_op_split(struct vm_area_struct *vma, unsigned long addr)
{
return -EINVAL;
@@ -61,9 +123,54 @@ static int mshare_vm_op_mprotect(struct vm_area_struct *vma, unsigned long start
return -EINVAL;
}
+/*
+ * Unlink any shared page tables in the range and ensure TLBs are flushed.
+ * Pages in the mshare region itself are not unmapped.
+ */
+static void mshare_vm_op_unshare_page_range(struct mmu_gather *tlb,
+ struct vm_area_struct *vma,
+ unsigned long addr, unsigned long end,
+ struct zap_details *details)
+{
+ struct mm_struct *mm = vma->vm_mm;
+ spinlock_t *ptl = &mm->page_table_lock;
+ unsigned long sz = mshare_align;
+ pgd_t *pgd;
+ p4d_t *p4d;
+ pud_t *pud;
+
+ WARN_ON(!vma_is_mshare(vma));
+
+ tlb_start_vma(tlb, vma);
+
+ for (; addr < end ; addr += sz) {
+ spin_lock(ptl);
+
+ pgd = pgd_offset(mm, addr);
+ if (!pgd_present(*pgd)) {
+ spin_unlock(ptl);
+ continue;
+ }
+ p4d = p4d_offset(pgd, addr);
+ if (!p4d_present(*p4d)) {
+ spin_unlock(ptl);
+ continue;
+ }
+ pud = p4d_pgtable(*p4d);
+ ptdesc_pud_pts_dec(virt_to_ptdesc(pud));
+
+ p4d_clear(p4d);
+ spin_unlock(ptl);
+ tlb_flush_p4d_range(tlb, addr, sz);
+ }
+
+ tlb_end_vma(tlb, vma);
+}
+
static const struct vm_operations_struct msharefs_vm_ops = {
.may_split = mshare_vm_op_split,
.mprotect = mshare_vm_op_mprotect,
+ .unmap_page_range = mshare_vm_op_unshare_page_range,
};
/*
--
2.47.1
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