[PATCH 4.14 056/106] hugetlbfs: flush TLBs correctly after huge_pmd_unshare

Greg Kroah-Hartman
2021-12-06T15:10:29Z

From: Nadav Amit <namit@vmware.com>

commit a4a118f2eead1d6c49e00765de89878288d4b890 upstream.

When __unmap_hugepage_range() calls to huge_pmd_unshare() succeed, a TLB
flush is missing. This TLB flush must be performed before releasing the
i_mmap_rwsem, in order to prevent an unshared PMDs page from being
released and reused before the TLB flush took place.

Arguably, a comprehensive solution would use mmu_gather interface to
batch the TLB flushes and the PMDs page release, however it is not an
easy solution: (1) try_to_unmap_one() and try_to_migrate_one() also call
huge_pmd_unshare() and they cannot use the mmu_gather interface; and (2)
deferring the release of the page reference for the PMDs page until
after i_mmap_rwsem is dropeed can confuse huge_pmd_unshare() into
thinking PMDs are shared when they are not.

Fix __unmap_hugepage_range() by adding the missing TLB flush, and
forcing a flush when unshare is successful.

Fixes: 24669e58477e ("hugetlb: use mmu_gather instead of a temporary linked list for accumulating pages)" # 3.6
Signed-off-by: Nadav Amit <namit@vmware.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm/include/asm/tlb.h | 8 ++++++++
arch/ia64/include/asm/tlb.h | 10 ++++++++++
arch/s390/include/asm/tlb.h | 14 ++++++++++++++
arch/sh/include/asm/tlb.h | 10 ++++++++++
arch/um/include/asm/tlb.h | 12 ++++++++++++
include/asm-generic/tlb.h | 2 ++
mm/hugetlb.c | 19 +++++++++++++++++++
mm/memory.c | 10 ++++++++++
8 files changed, 85 insertions(+)

--- a/arch/arm/include/asm/tlb.h
+++ b/arch/arm/include/asm/tlb.h
@@ -280,6 +280,14 @@ tlb_remove_pmd_tlb_entry(struct mmu_gath
tlb_add_flush(tlb, addr);
}

+static inline void
+tlb_flush_pmd_range(struct mmu_gather *tlb, unsigned long address,
+ unsigned long size)
+{
+ tlb_add_flush(tlb, address);
+ tlb_add_flush(tlb, address + size - PMD_SIZE);
+}
+
#define pte_free_tlb(tlb, ptep, addr) __pte_free_tlb(tlb, ptep, addr)
#define pmd_free_tlb(tlb, pmdp, addr) __pmd_free_tlb(tlb, pmdp, addr)
#define pud_free_tlb(tlb, pudp, addr) pud_free((tlb)->mm, pudp)
--- a/arch/ia64/include/asm/tlb.h
+++ b/arch/ia64/include/asm/tlb.h
@@ -269,6 +269,16 @@ __tlb_remove_tlb_entry (struct mmu_gathe
tlb->end_addr = address + PAGE_SIZE;
}

+static inline void
+tlb_flush_pmd_range(struct mmu_gather *tlb, unsigned long address,
+ unsigned long size)
+{
+ if (tlb->start_addr > address)
+ tlb->start_addr = address;
+ if (tlb->end_addr < address + size)
+ tlb->end_addr = address + size;
+}
+
#define tlb_migrate_finish(mm) platform_tlb_migrate_finish(mm)

#define tlb_start_vma(tlb, vma) do { } while (0)
--- a/arch/s390/include/asm/tlb.h
+++ b/arch/s390/include/asm/tlb.h
@@ -116,6 +116,20 @@ static inline void tlb_remove_page_size(
return tlb_remove_page(tlb, page);
}

+static inline void tlb_flush_pmd_range(struct mmu_gather *tlb,
+ unsigned long address, unsigned long size)
+{
+ /*
+ * the range might exceed the original range that was provided to
+ * tlb_gather_mmu(), so we need to update it despite the fact it is
+ * usually not updated.
+ */
+ if (tlb->start > address)
+ tlb->start = address;
+ if (tlb->end < address + size)
+ tlb->end = address + size;
+}
+
/*
* pte_free_tlb frees a pte table and clears the CRSTE for the
* page table from the tlb.
--- a/arch/sh/include/asm/tlb.h
+++ b/arch/sh/include/asm/tlb.h
@@ -127,6 +127,16 @@ static inline void tlb_remove_page_size(
return tlb_remove_page(tlb, page);
}

+static inline void
+tlb_flush_pmd_range(struct mmu_gather *tlb, unsigned long address,
+ unsigned long size)
+{
+ if (tlb->start > address)
+ tlb->start = address;
+ if (tlb->end < address + size)
+ tlb->end = address + size;
+}
+
#define tlb_remove_check_page_size_change tlb_remove_check_page_size_change
static inline void tlb_remove_check_page_size_change(struct mmu_gather *tlb,
unsigned int page_size)
--- a/arch/um/include/asm/tlb.h
+++ b/arch/um/include/asm/tlb.h
@@ -130,6 +130,18 @@ static inline void tlb_remove_page_size(
return tlb_remove_page(tlb, page);
}

+static inline void
+tlb_flush_pmd_range(struct mmu_gather *tlb, unsigned long address,
+ unsigned long size)
+{
+ tlb->need_flush = 1;
+
+ if (tlb->start > address)
+ tlb->start = address;
+ if (tlb->end < address + size)
+ tlb->end = address + size;
+}
+
/**
* tlb_remove_tlb_entry - remember a pte unmapping for later tlb invalidation.
*
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -117,6 +117,8 @@ void arch_tlb_gather_mmu(struct mmu_gath
void tlb_flush_mmu(struct mmu_gather *tlb);
void arch_tlb_finish_mmu(struct mmu_gather *tlb,
unsigned long start, unsigned long end, bool force);
+void tlb_flush_pmd_range(struct mmu_gather *tlb, unsigned long address,
+ unsigned long size);
extern bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page,
int page_size);

--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3386,6 +3386,7 @@ void __unmap_hugepage_range(struct mmu_g
unsigned long sz = huge_page_size(h);
const unsigned long mmun_start = start; /* For mmu_notifiers */
const unsigned long mmun_end = end; /* For mmu_notifiers */
+ bool force_flush = false;

WARN_ON(!is_vm_hugetlb_page(vma));
BUG_ON(start & ~huge_page_mask(h));
@@ -3407,6 +3408,8 @@ void __unmap_hugepage_range(struct mmu_g
ptl = huge_pte_lock(h, mm, ptep);
if (huge_pmd_unshare(mm, &address, ptep)) {
spin_unlock(ptl);
+ tlb_flush_pmd_range(tlb, address & PUD_MASK, PUD_SIZE);
+ force_flush = true;
continue;
}

@@ -3463,6 +3466,22 @@ void __unmap_hugepage_range(struct mmu_g
}
mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
tlb_end_vma(tlb, vma);
+
+ /*
+ * If we unshared PMDs, the TLB flush was not recorded in mmu_gather. We
+ * could defer the flush until now, since by holding i_mmap_rwsem we
+ * guaranteed that the last refernece would not be dropped. But we must
+ * do the flushing before we return, as otherwise i_mmap_rwsem will be
+ * dropped and the last reference to the shared PMDs page might be
+ * dropped as well.
+ *
+ * In theory we could defer the freeing of the PMD pages as well, but
+ * huge_pmd_unshare() relies on the exact page_count for the PMD page to
+ * detect sharing, so we cannot defer the release of the page either.
+ * Instead, do flush now.
+ */
+ if (force_flush)
+ tlb_flush_mmu(tlb);
}

void __unmap_hugepage_range_final(struct mmu_gather *tlb,
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -335,6 +335,16 @@ bool __tlb_remove_page_size(struct mmu_g
return false;
}

+void tlb_flush_pmd_range(struct mmu_gather *tlb, unsigned long address,
+ unsigned long size)
+{
+ if (tlb->page_size != 0 && tlb->page_size != PMD_SIZE)
+ tlb_flush_mmu(tlb);
+
+ tlb->page_size = PMD_SIZE;
+ tlb->start = min(tlb->start, address);
+ tlb->end = max(tlb->end, address + size);
+}
#endif /* HAVE_GENERIC_MMU_GATHER */

#ifdef CONFIG_HAVE_RCU_TABLE_FREE