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Message-ID: <20250124235454.84587-13-anthony.yznaga@oracle.com>
Date: Fri, 24 Jan 2025 15:54:46 -0800
From: Anthony Yznaga <anthony.yznaga@...cle.com>
To: akpm@...ux-foundation.org, willy@...radead.org, markhemm@...glemail.com,
viro@...iv.linux.org.uk, david@...hat.com, khalid@...nel.org
Cc: anthony.yznaga@...cle.com, jthoughton@...gle.com, corbet@....net,
dave.hansen@...el.com, kirill@...temov.name, luto@...nel.org,
brauner@...nel.org, arnd@...db.de, ebiederm@...ssion.com,
catalin.marinas@....com, mingo@...hat.com, peterz@...radead.org,
liam.howlett@...cle.com, lorenzo.stoakes@...cle.com, vbabka@...e.cz,
jannh@...gle.com, hannes@...xchg.org, mhocko@...nel.org,
roman.gushchin@...ux.dev, shakeel.butt@...ux.dev,
muchun.song@...ux.dev, tglx@...utronix.de, cgroups@...r.kernel.org,
x86@...nel.org, linux-doc@...r.kernel.org, linux-arch@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org, mhiramat@...nel.org,
rostedt@...dmis.org, vasily.averin@...ux.dev, xhao@...ux.alibaba.com,
pcc@...gle.com, neilb@...e.de, maz@...nel.org
Subject: [PATCH 12/20] 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. Modify the unmap path to ensure that page tables in mshare regions
are unlinked and kept intact 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 | 38 ++++++++++++++++++++++------
mm/mshare.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 98 insertions(+), 8 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 1314af11596d..9889c4757f45 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1110,11 +1110,17 @@ 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 20bafbb10ea7..9374bb184a5f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -263,7 +263,8 @@ static inline void free_pud_range(struct mmu_gather *tlb, p4d_t *p4d,
static inline void free_p4d_range(struct mmu_gather *tlb, pgd_t *pgd,
unsigned long addr, unsigned long end,
- unsigned long floor, unsigned long ceiling)
+ unsigned long floor, unsigned long ceiling,
+ bool shared_pud)
{
p4d_t *p4d;
unsigned long next;
@@ -275,7 +276,10 @@ static inline void free_p4d_range(struct mmu_gather *tlb, pgd_t *pgd,
next = p4d_addr_end(addr, end);
if (p4d_none_or_clear_bad(p4d))
continue;
- free_pud_range(tlb, p4d, addr, next, floor, ceiling);
+ if (unlikely(shared_pud))
+ p4d_clear(p4d);
+ else
+ free_pud_range(tlb, p4d, addr, next, floor, ceiling);
} while (p4d++, addr = next, addr != end);
start &= PGDIR_MASK;
@@ -297,9 +301,10 @@ static inline void free_p4d_range(struct mmu_gather *tlb, pgd_t *pgd,
/*
* This function frees user-level page tables of a process.
*/
-void free_pgd_range(struct mmu_gather *tlb,
+static void __free_pgd_range(struct mmu_gather *tlb,
unsigned long addr, unsigned long end,
- unsigned long floor, unsigned long ceiling)
+ unsigned long floor, unsigned long ceiling,
+ bool shared_pud)
{
pgd_t *pgd;
unsigned long next;
@@ -355,10 +360,17 @@ void free_pgd_range(struct mmu_gather *tlb,
next = pgd_addr_end(addr, end);
if (pgd_none_or_clear_bad(pgd))
continue;
- free_p4d_range(tlb, pgd, addr, next, floor, ceiling);
+ free_p4d_range(tlb, pgd, addr, next, floor, ceiling, shared_pud);
} while (pgd++, addr = next, addr != end);
}
+void free_pgd_range(struct mmu_gather *tlb,
+ unsigned long addr, unsigned long end,
+ unsigned long floor, unsigned long ceiling)
+{
+ __free_pgd_range(tlb, addr, end, floor, ceiling, false);
+}
+
void free_pgtables(struct mmu_gather *tlb, struct ma_state *mas,
struct vm_area_struct *vma, unsigned long floor,
unsigned long ceiling, bool mm_wr_locked)
@@ -395,9 +407,12 @@ void free_pgtables(struct mmu_gather *tlb, struct ma_state *mas,
/*
* Optimization: gather nearby vmas into one call down
+ *
+ * Do not free the shared page tables of an mshare region.
*/
while (next && next->vm_start <= vma->vm_end + PMD_SIZE
- && !is_vm_hugetlb_page(next)) {
+ && !is_vm_hugetlb_page(next)
+ && !vma_is_mshare(next)) {
vma = next;
next = mas_find(mas, ceiling - 1);
if (unlikely(xa_is_zero(next)))
@@ -408,9 +423,11 @@ void free_pgtables(struct mmu_gather *tlb, struct ma_state *mas,
unlink_file_vma_batch_add(&vb, vma);
}
unlink_file_vma_batch_final(&vb);
- free_pgd_range(tlb, addr, vma->vm_end,
- floor, next ? next->vm_start : ceiling);
+ __free_pgd_range(tlb, addr, vma->vm_end,
+ floor, next ? next->vm_start : ceiling,
+ vma_is_mshare(vma));
}
+
vma = next;
} while (vma);
}
@@ -6148,6 +6165,11 @@ 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);
+ return VM_FAULT_SIGBUS;
+ }
+
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 8dca4199dd01..9ada1544aeb1 100644
--- a/mm/mshare.c
+++ b/mm/mshare.c
@@ -42,6 +42,56 @@ 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)) {
+ set_p4d(guest_p4d, *p4d);
+ mmap_read_unlock(host_mm);
+ return VM_FAULT_NOPAGE;
+ }
+
+ *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;
@@ -53,9 +103,21 @@ static int mshare_vm_op_mprotect(struct vm_area_struct *vma, unsigned long start
return -EINVAL;
}
+static void mshare_vm_op_unmap_page_range(struct mmu_gather *tlb,
+ struct vm_area_struct *vma,
+ unsigned long addr, unsigned long end,
+ struct zap_details *details)
+{
+ /*
+ * The msharefs vma is being unmapped. Do not unmap pages in the
+ * mshare region itself.
+ */
+}
+
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_unmap_page_range,
};
/*
--
2.43.5
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