[PATCH v3 3/8] mm: drop per-VMA lock in handle_mm_fault if retrying or when finished

Suren Baghdasaryan
2023-06-27T04:23:35Z

handle_mm_fault returning VM_FAULT_RETRY or VM_FAULT_COMPLETED means
mmap_lock has been released. However with per-VMA locks behavior is
different and the caller should still release it. To make the
rules consistent for the caller, drop the per-VMA lock before returning
from handle_mm_fault when page fault should be retried or is completed.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
arch/arm64/mm/fault.c | 3 ++-
arch/powerpc/mm/fault.c | 3 ++-
arch/s390/mm/fault.c | 3 ++-
arch/x86/mm/fault.c | 3 ++-
mm/memory.c | 12 +++++++++++-
5 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 6045a5117ac1..89f84e9ea1ff 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -601,7 +601,8 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
goto lock_mmap;
}
fault = handle_mm_fault(vma, addr, mm_flags | FAULT_FLAG_VMA_LOCK, regs);
- vma_end_read(vma);
+ if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
+ vma_end_read(vma);

if (!(fault & VM_FAULT_RETRY)) {
count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 531177a4ee08..4697c5dca31c 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -494,7 +494,8 @@ static int ___do_page_fault(struct pt_regs *regs, unsigned long address,
}

fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs);
- vma_end_read(vma);
+ if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
+ vma_end_read(vma);

if (!(fault & VM_FAULT_RETRY)) {
count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index b65144c392b0..cccefe41038b 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -418,7 +418,8 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
goto lock_mmap;
}
fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs);
- vma_end_read(vma);
+ if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
+ vma_end_read(vma);
if (!(fault & VM_FAULT_RETRY)) {
count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
goto out;
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index e4399983c50c..d69c85c1c04e 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1347,7 +1347,8 @@ void do_user_addr_fault(struct pt_regs *regs,
goto lock_mmap;
}
fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs);
- vma_end_read(vma);
+ if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
+ vma_end_read(vma);

if (!(fault & VM_FAULT_RETRY)) {
count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
diff --git a/mm/memory.c b/mm/memory.c
index f69fbc251198..9011ad63c41b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5086,7 +5086,17 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
}
}

- return handle_pte_fault(&vmf);
+ ret = handle_pte_fault(&vmf);
+ if (ret & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)) {
+ /*
+ * In case of VM_FAULT_RETRY or VM_FAULT_COMPLETED we might
+ * be still holding per-VMA lock to keep the vma stable as long
+ * as possible. Drop it before returning.
+ */
+ if (vmf.flags & FAULT_FLAG_VMA_LOCK)
+ vma_end_read(vma);
+ }
+ return ret;
}

/**
--
2.41.0.178.g377b9f9a00-goog