From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id 5DC806B0279 for ; Thu, 25 May 2017 13:33:42 -0400 (EDT) Received: by mail-pf0-f198.google.com with SMTP id e131so236208283pfh.7 for ; Thu, 25 May 2017 10:33:42 -0700 (PDT) Received: from foss.arm.com (foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id i14si28677702plk.84.2017.05.25.10.33.41 for ; Thu, 25 May 2017 10:33:41 -0700 (PDT) From: Punit Agrawal Subject: Re: [PATCH v2] mm/hugetlb: Report -EHWPOISON not -EFAULT when FOLL_HWPOISON is specified References: <20170525171035.16359-1-james.morse@arm.com> Date: Thu, 25 May 2017 18:33:38 +0100 In-Reply-To: <20170525171035.16359-1-james.morse@arm.com> (James Morse's message of "Thu, 25 May 2017 18:10:35 +0100") Message-ID: <87y3tkdeod.fsf@e105922-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org List-ID: To: James Morse Cc: linux-mm@kvack.org, "Kirill A . Shutemov" , Andrew Morton , Naoya Horiguchi James Morse writes: > 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. > > 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(), follow_hugetlb_page() and faultin_page(). You've got faultin_page() listed twice - I think you meant to add fixup_user_fault(). With that addressed, Acked-by: Punit Agrawal > > With this, KVM works as expected. > > CC: Punit Agrawal > CC: Naoya Horiguchi > Signed-off-by: James Morse > --- > Changes since v1: > * Fixed checkpatch warnings (oops, wrong file) > * Added vm_fault_to_errno() call to faultin_page() as Naoya Horiguchi > suggested. > > 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. My best offer is: > Cc: # 4.11.1 > > include/linux/mm.h | 11 +++++++++++ > mm/gup.c | 20 ++++++++------------ > mm/hugetlb.c | 5 +++++ > 3 files changed, 24 insertions(+), 12 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 7cb17c6b97de..b892e95d4929 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -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_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, > void *data); > extern int apply_to_page_range(struct mm_struct *mm, unsigned long address, > diff --git a/mm/gup.c b/mm/gup.c > index d9e6fddcc51f..b3c7214d710d 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -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); > if (ret & VM_FAULT_ERROR) { > - if (ret & VM_FAULT_OOM) > - return -ENOMEM; > - if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE)) > - return *flags & FOLL_HWPOISON ? -EHWPOISON : -EFAULT; > - if (ret & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV)) > - return -EFAULT; > + int err = vm_fault_to_errno(ret, *flags); > + > + if (err) > + return err; > 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); > major |= ret & VM_FAULT_MAJOR; > if (ret & VM_FAULT_ERROR) { > - if (ret & VM_FAULT_OOM) > - return -ENOMEM; > - if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE)) > - return -EHWPOISON; > - if (ret & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV)) > - return -EFAULT; > + int err = vm_fault_to_errno(ret, 0); > + > + if (err) > + return err; > BUG(); > } > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index e5828875f7bb..3eedb187e549 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -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); > if (ret & VM_FAULT_ERROR) { > + int err = vm_fault_to_errno(ret, flags); > + > + if (err) > + return err; > + > remainder = 0; > break; > } -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org