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Commit 9a291a7c authored by James Morse's avatar James Morse Committed by Linus Torvalds
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mm/hugetlb: report -EHWPOISON not -EFAULT when FOLL_HWPOISON is specified 

KVM uses get_user_pages() to resolve its stage2 faults.  KVM sets the
FOLL_HWPOISON flag causing faultin_page() to return -EHWPOISON when it
finds a VM_FAULT_HWPOISON.  KVM handles these hwpoison pages as a
special case.  (check_user_page_hwpoison())

When huge pages are involved, this doesn't work so well.
get_user_pages() calls follow_hugetlb_page(), which stops early if it
receives VM_FAULT_HWPOISON from hugetlb_fault(), eventually returning
-EFAULT to the caller.  The step to map this to -EHWPOISON based on the
FOLL_ flags is missing.  The hwpoison special case is skipped, and
-EFAULT is returned to user-space, causing Qemu or kvmtool to exit.

Instead, move this VM_FAULT_ to errno mapping code into a header file
and use it from faultin_page() and follow_hugetlb_page().

With this, KVM works as expected.

This isn't a problem for arm64 today as we haven't enabled
MEMORY_FAILURE, but I can't see any reason this doesn't happen on x86
too, so I think this should be a fix.  This doesn't apply earlier than
stable's v4.11.1 due to all sorts of cleanup.

[james.morse@arm.com: add vm_fault_to_errno() call to faultin_page()]
suggested.
  Link: http://lkml.kernel.org/r/20170525171035.16359-1-james.morse@arm.com
[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/20170524160900.28786-1-james.morse@arm.com


Signed-off-by: default avatarJames Morse <james.morse@arm.com>
Acked-by: default avatarPunit Agrawal <punit.agrawal@arm.com>
Acked-by: default avatarNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: <stable@vger.kernel.org>	[4.11.1+]
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 70feee0e

include/linux/mm.h

+11 −0
Original line number Original line Diff line number Diff line
@@ -2327,6 +2327,17 @@ static inline struct page *follow_page(struct vm_area_struct *vma, 
#define FOLL_REMOTE	0x2000	/* we are working on non-current tsk/mm */

#define FOLL_REMOTE	0x2000	/* we are working on non-current tsk/mm */

#define FOLL_COW	0x4000	/* internal GUP flag */

#define FOLL_COW	0x4000	/* internal GUP flag */





static inline int vm_fault_to_errno(int vm_fault, int foll_flags)

{

	if (vm_fault & VM_FAULT_OOM)

		return -ENOMEM;

	if (vm_fault & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))

		return (foll_flags & FOLL_HWPOISON) ? -EHWPOISON : -EFAULT;

	if (vm_fault & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV))

		return -EFAULT;

	return 0;

}



typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,

typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,

			void *data);

			void *data);

extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,

extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,

mm/gup.c

+8 −12
Original line number Original line Diff line number Diff line
@@ -407,12 +407,10 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma, 




	ret = handle_mm_fault(vma, address, fault_flags);

	ret = handle_mm_fault(vma, address, fault_flags);

	if (ret & VM_FAULT_ERROR) {

	if (ret & VM_FAULT_ERROR) {

		if (ret & VM_FAULT_OOM)

		int err = vm_fault_to_errno(ret, *flags);

			return -ENOMEM;



		if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))

		if (err)

			return *flags & FOLL_HWPOISON ? -EHWPOISON : -EFAULT;

			return err;

		if (ret & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV))

			return -EFAULT;

		BUG();

		BUG();

	}

	}
@@ -723,12 +721,10 @@ int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm, 
	ret = handle_mm_fault(vma, address, fault_flags);

	ret = handle_mm_fault(vma, address, fault_flags);

	major |= ret & VM_FAULT_MAJOR;

	major |= ret & VM_FAULT_MAJOR;

	if (ret & VM_FAULT_ERROR) {

	if (ret & VM_FAULT_ERROR) {

		if (ret & VM_FAULT_OOM)

		int err = vm_fault_to_errno(ret, 0);

			return -ENOMEM;



		if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))

		if (err)

			return -EHWPOISON;

			return err;

		if (ret & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV))

			return -EFAULT;

		BUG();

		BUG();

	}

	}

mm/hugetlb.c

+5 −0
Original line number Original line Diff line number Diff line
@@ -4170,6 +4170,11 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, 
			}

			}

			ret = hugetlb_fault(mm, vma, vaddr, fault_flags);

			ret = hugetlb_fault(mm, vma, vaddr, fault_flags);

			if (ret & VM_FAULT_ERROR) {

			if (ret & VM_FAULT_ERROR) {

				int err = vm_fault_to_errno(ret, flags);



				if (err)

					return err;



				remainder = 0;

				remainder = 0;

				break;

				break;

			}

			}