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linux-stable/include/trace/events/mmflags.h
Axel Rasmussen 7677f7fd8b userfaultfd: add minor fault registration mode 
Patch series "userfaultfd: add minor fault handling", v9.

Overview
========

This series adds a new userfaultfd feature, UFFD_FEATURE_MINOR_HUGETLBFS.
When enabled (via the UFFDIO_API ioctl), this feature means that any
hugetlbfs VMAs registered with UFFDIO_REGISTER_MODE_MISSING will *also*
get events for "minor" faults.  By "minor" fault, I mean the following
situation:

Let there exist two mappings (i.e., VMAs) to the same page(s) (shared
memory).  One of the mappings is registered with userfaultfd (in minor
mode), and the other is not.  Via the non-UFFD mapping, the underlying
pages have already been allocated & filled with some contents.  The UFFD
mapping has not yet been faulted in; when it is touched for the first
time, this results in what I'm calling a "minor" fault.  As a concrete
example, when working with hugetlbfs, we have huge_pte_none(), but
find_lock_page() finds an existing page.

We also add a new ioctl to resolve such faults: UFFDIO_CONTINUE.  The idea
is, userspace resolves the fault by either a) doing nothing if the
contents are already correct, or b) updating the underlying contents using
the second, non-UFFD mapping (via memcpy/memset or similar, or something
fancier like RDMA, or etc...).  In either case, userspace issues
UFFDIO_CONTINUE to tell the kernel "I have ensured the page contents are
correct, carry on setting up the mapping".

Use Case
========

Consider the use case of VM live migration (e.g. under QEMU/KVM):

1. While a VM is still running, we copy the contents of its memory to a
   target machine. The pages are populated on the target by writing to the
   non-UFFD mapping, using the setup described above. The VM is still running
   (and therefore its memory is likely changing), so this may be repeated
   several times, until we decide the target is "up to date enough".

2. We pause the VM on the source, and start executing on the target machine.
   During this gap, the VM's user(s) will *see* a pause, so it is desirable to
   minimize this window.

3. Between the last time any page was copied from the source to the target, and
   when the VM was paused, the contents of that page may have changed - and
   therefore the copy we have on the target machine is out of date. Although we
   can keep track of which pages are out of date, for VMs with large amounts of
   memory, it is "slow" to transfer this information to the target machine. We
   want to resume execution before such a transfer would complete.

4. So, the guest begins executing on the target machine. The first time it
   touches its memory (via the UFFD-registered mapping), userspace wants to
   intercept this fault. Userspace checks whether or not the page is up to date,
   and if not, copies the updated page from the source machine, via the non-UFFD
   mapping. Finally, whether a copy was performed or not, userspace issues a
   UFFDIO_CONTINUE ioctl to tell the kernel "I have ensured the page contents
   are correct, carry on setting up the mapping".

We don't have to do all of the final updates on-demand. The userfaultfd manager
can, in the background, also copy over updated pages once it receives the map of
which pages are up-to-date or not.

Interaction with Existing APIs
==============================

Because this is a feature, a registered VMA could potentially receive both
missing and minor faults.  I spent some time thinking through how the
existing API interacts with the new feature:

UFFDIO_CONTINUE cannot be used to resolve non-minor faults, as it does not
allocate a new page.  If UFFDIO_CONTINUE is used on a non-minor fault:

- For non-shared memory or shmem, -EINVAL is returned.
- For hugetlb, -EFAULT is returned.

UFFDIO_COPY and UFFDIO_ZEROPAGE cannot be used to resolve minor faults.
Without modifications, the existing codepath assumes a new page needs to
be allocated.  This is okay, since userspace must have a second
non-UFFD-registered mapping anyway, thus there isn't much reason to want
to use these in any case (just memcpy or memset or similar).

- If UFFDIO_COPY is used on a minor fault, -EEXIST is returned.
- If UFFDIO_ZEROPAGE is used on a minor fault, -EEXIST is returned (or -EINVAL
  in the case of hugetlb, as UFFDIO_ZEROPAGE is unsupported in any case).
- UFFDIO_WRITEPROTECT simply doesn't work with shared memory, and returns
  -ENOENT in that case (regardless of the kind of fault).

Future Work
===========

This series only supports hugetlbfs.  I have a second series in flight to
support shmem as well, extending the functionality.  This series is more
mature than the shmem support at this point, and the functionality works
fully on hugetlbfs, so this series can be merged first and then shmem
support will follow.

This patch (of 6):

This feature allows userspace to intercept "minor" faults.  By "minor"
faults, I mean the following situation:

Let there exist two mappings (i.e., VMAs) to the same page(s).  One of the
mappings is registered with userfaultfd (in minor mode), and the other is
not.  Via the non-UFFD mapping, the underlying pages have already been
allocated & filled with some contents.  The UFFD mapping has not yet been
faulted in; when it is touched for the first time, this results in what
I'm calling a "minor" fault.  As a concrete example, when working with
hugetlbfs, we have huge_pte_none(), but find_lock_page() finds an existing
page.

This commit adds the new registration mode, and sets the relevant flag on
the VMAs being registered.  In the hugetlb fault path, if we find that we
have huge_pte_none(), but find_lock_page() does indeed find an existing
page, then we have a "minor" fault, and if the VMA has the userfaultfd
registration flag, we call into userfaultfd to handle it.

This is implemented as a new registration mode, instead of an API feature.
This is because the alternative implementation has significant drawbacks
[1].

However, doing it this was requires we allocate a VM_* flag for the new
registration mode.  On 32-bit systems, there are no unused bits, so this
feature is only supported on architectures with
CONFIG_ARCH_USES_HIGH_VMA_FLAGS.  When attempting to register a VMA in
MINOR mode on 32-bit architectures, we return -EINVAL.

[1] https://lore.kernel.org/patchwork/patch/1380226/

[peterx@redhat.com: fix minor fault page leak]
  Link: https://lkml.kernel.org/r/20210322175132.36659-1-peterx@redhat.com

Link: https://lkml.kernel.org/r/20210301222728.176417-1-axelrasmussen@google.com
Link: https://lkml.kernel.org/r/20210301222728.176417-2-axelrasmussen@google.com
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chinwen Chang <chinwen.chang@mediatek.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: "Michal Koutn" <mkoutny@suse.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shaohua Li <shli@fb.com>
Cc: Shawn Anastasio <shawn@anastas.io>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Adam Ruprecht <ruprecht@google.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Cannon Matthews <cannonmatthews@google.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Oliver Upton <oupton@google.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-05-05 11:27:22 -07:00

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/* SPDX-License-Identifier: GPL-2.0 */
#include <linux/node.h>
#include <linux/mmzone.h>
#include <linux/compaction.h>
/*
* The order of these masks is important. Matching masks will be seen
* first and the left over flags will end up showing by themselves.
*
* For example, if we have GFP_KERNEL before GFP_USER we wil get:
*
* GFP_KERNEL|GFP_HARDWALL
*
* Thus most bits set go first.
*/
#define __def_gfpflag_names \
{(unsigned long)GFP_TRANSHUGE, "GFP_TRANSHUGE"}, \
{(unsigned long)GFP_TRANSHUGE_LIGHT, "GFP_TRANSHUGE_LIGHT"}, \
{(unsigned long)GFP_HIGHUSER_MOVABLE, "GFP_HIGHUSER_MOVABLE"},\
{(unsigned long)GFP_HIGHUSER, "GFP_HIGHUSER"}, \
{(unsigned long)GFP_USER, "GFP_USER"}, \
{(unsigned long)GFP_KERNEL_ACCOUNT, "GFP_KERNEL_ACCOUNT"}, \
{(unsigned long)GFP_KERNEL, "GFP_KERNEL"}, \
{(unsigned long)GFP_NOFS, "GFP_NOFS"}, \
{(unsigned long)GFP_ATOMIC, "GFP_ATOMIC"}, \
{(unsigned long)GFP_NOIO, "GFP_NOIO"}, \
{(unsigned long)GFP_NOWAIT, "GFP_NOWAIT"}, \
{(unsigned long)GFP_DMA, "GFP_DMA"}, \
{(unsigned long)__GFP_HIGHMEM, "__GFP_HIGHMEM"}, \
{(unsigned long)GFP_DMA32, "GFP_DMA32"}, \
{(unsigned long)__GFP_HIGH, "__GFP_HIGH"}, \
{(unsigned long)__GFP_ATOMIC, "__GFP_ATOMIC"}, \
{(unsigned long)__GFP_IO, "__GFP_IO"}, \
{(unsigned long)__GFP_FS, "__GFP_FS"}, \
{(unsigned long)__GFP_NOWARN, "__GFP_NOWARN"}, \
{(unsigned long)__GFP_RETRY_MAYFAIL, "__GFP_RETRY_MAYFAIL"}, \
{(unsigned long)__GFP_NOFAIL, "__GFP_NOFAIL"}, \
{(unsigned long)__GFP_NORETRY, "__GFP_NORETRY"}, \
{(unsigned long)__GFP_COMP, "__GFP_COMP"}, \
{(unsigned long)__GFP_ZERO, "__GFP_ZERO"}, \
{(unsigned long)__GFP_NOMEMALLOC, "__GFP_NOMEMALLOC"}, \
{(unsigned long)__GFP_MEMALLOC, "__GFP_MEMALLOC"}, \
{(unsigned long)__GFP_HARDWALL, "__GFP_HARDWALL"}, \
{(unsigned long)__GFP_THISNODE, "__GFP_THISNODE"}, \
{(unsigned long)__GFP_RECLAIMABLE, "__GFP_RECLAIMABLE"}, \
{(unsigned long)__GFP_MOVABLE, "__GFP_MOVABLE"}, \
{(unsigned long)__GFP_ACCOUNT, "__GFP_ACCOUNT"}, \
{(unsigned long)__GFP_WRITE, "__GFP_WRITE"}, \
{(unsigned long)__GFP_RECLAIM, "__GFP_RECLAIM"}, \
{(unsigned long)__GFP_DIRECT_RECLAIM, "__GFP_DIRECT_RECLAIM"},\
{(unsigned long)__GFP_KSWAPD_RECLAIM, "__GFP_KSWAPD_RECLAIM"}\
#define show_gfp_flags(flags) \
(flags) ? __print_flags(flags, "|", \
__def_gfpflag_names \
) : "none"
#ifdef CONFIG_MMU
#define IF_HAVE_PG_MLOCK(flag,string) ,{1UL << flag, string}
#else
#define IF_HAVE_PG_MLOCK(flag,string)
#endif
#ifdef CONFIG_ARCH_USES_PG_UNCACHED
#define IF_HAVE_PG_UNCACHED(flag,string) ,{1UL << flag, string}
#else
#define IF_HAVE_PG_UNCACHED(flag,string)
#endif
#ifdef CONFIG_MEMORY_FAILURE
#define IF_HAVE_PG_HWPOISON(flag,string) ,{1UL << flag, string}
#else
#define IF_HAVE_PG_HWPOISON(flag,string)
#endif
#if defined(CONFIG_IDLE_PAGE_TRACKING) && defined(CONFIG_64BIT)
#define IF_HAVE_PG_IDLE(flag,string) ,{1UL << flag, string}
#else
#define IF_HAVE_PG_IDLE(flag,string)
#endif
#ifdef CONFIG_64BIT
#define IF_HAVE_PG_ARCH_2(flag,string) ,{1UL << flag, string}
#else
#define IF_HAVE_PG_ARCH_2(flag,string)
#endif
#define __def_pageflag_names \
{1UL << PG_locked, "locked" }, \
{1UL << PG_waiters, "waiters" }, \
{1UL << PG_error, "error" }, \
{1UL << PG_referenced, "referenced" }, \
{1UL << PG_uptodate, "uptodate" }, \
{1UL << PG_dirty, "dirty" }, \
{1UL << PG_lru, "lru" }, \
{1UL << PG_active, "active" }, \
{1UL << PG_workingset, "workingset" }, \
{1UL << PG_slab, "slab" }, \
{1UL << PG_owner_priv_1, "owner_priv_1" }, \
{1UL << PG_arch_1, "arch_1" }, \
{1UL << PG_reserved, "reserved" }, \
{1UL << PG_private, "private" }, \
{1UL << PG_private_2, "private_2" }, \
{1UL << PG_writeback, "writeback" }, \
{1UL << PG_head, "head" }, \
{1UL << PG_mappedtodisk, "mappedtodisk" }, \
{1UL << PG_reclaim, "reclaim" }, \
{1UL << PG_swapbacked, "swapbacked" }, \
{1UL << PG_unevictable, "unevictable" } \
IF_HAVE_PG_MLOCK(PG_mlocked, "mlocked" ) \
IF_HAVE_PG_UNCACHED(PG_uncached, "uncached" ) \
IF_HAVE_PG_HWPOISON(PG_hwpoison, "hwpoison" ) \
IF_HAVE_PG_IDLE(PG_young, "young" ) \
IF_HAVE_PG_IDLE(PG_idle, "idle" ) \
IF_HAVE_PG_ARCH_2(PG_arch_2, "arch_2" )
#define show_page_flags(flags) \
(flags) ? __print_flags(flags, "|", \
__def_pageflag_names \
) : "none"
#if defined(CONFIG_X86)
#define __VM_ARCH_SPECIFIC_1 {VM_PAT, "pat" }
#elif defined(CONFIG_PPC)
#define __VM_ARCH_SPECIFIC_1 {VM_SAO, "sao" }
#elif defined(CONFIG_PARISC) || defined(CONFIG_IA64)
#define __VM_ARCH_SPECIFIC_1 {VM_GROWSUP, "growsup" }
#elif !defined(CONFIG_MMU)
#define __VM_ARCH_SPECIFIC_1 {VM_MAPPED_COPY,"mappedcopy" }
#else
#define __VM_ARCH_SPECIFIC_1 {VM_ARCH_1, "arch_1" }
#endif
#ifdef CONFIG_MEM_SOFT_DIRTY
#define IF_HAVE_VM_SOFTDIRTY(flag,name) {flag, name },
#else
#define IF_HAVE_VM_SOFTDIRTY(flag,name)
#endif
#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
# define IF_HAVE_UFFD_MINOR(flag, name) {flag, name},
#else
# define IF_HAVE_UFFD_MINOR(flag, name)
#endif
#define __def_vmaflag_names \
{VM_READ, "read" }, \
{VM_WRITE, "write" }, \
{VM_EXEC, "exec" }, \
{VM_SHARED, "shared" }, \
{VM_MAYREAD, "mayread" }, \
{VM_MAYWRITE, "maywrite" }, \
{VM_MAYEXEC, "mayexec" }, \
{VM_MAYSHARE, "mayshare" }, \
{VM_GROWSDOWN, "growsdown" }, \
{VM_UFFD_MISSING, "uffd_missing" }, \
IF_HAVE_UFFD_MINOR(VM_UFFD_MINOR, "uffd_minor" ) \
{VM_PFNMAP, "pfnmap" }, \
{VM_DENYWRITE, "denywrite" }, \
{VM_UFFD_WP, "uffd_wp" }, \
{VM_LOCKED, "locked" }, \
{VM_IO, "io" }, \
{VM_SEQ_READ, "seqread" }, \
{VM_RAND_READ, "randread" }, \
{VM_DONTCOPY, "dontcopy" }, \
{VM_DONTEXPAND, "dontexpand" }, \
{VM_LOCKONFAULT, "lockonfault" }, \
{VM_ACCOUNT, "account" }, \
{VM_NORESERVE, "noreserve" }, \
{VM_HUGETLB, "hugetlb" }, \
{VM_SYNC, "sync" }, \
__VM_ARCH_SPECIFIC_1 , \
{VM_WIPEONFORK, "wipeonfork" }, \
{VM_DONTDUMP, "dontdump" }, \
IF_HAVE_VM_SOFTDIRTY(VM_SOFTDIRTY, "softdirty" ) \
{VM_MIXEDMAP, "mixedmap" }, \
{VM_HUGEPAGE, "hugepage" }, \
{VM_NOHUGEPAGE, "nohugepage" }, \
{VM_MERGEABLE, "mergeable" } \
#define show_vma_flags(flags) \
(flags) ? __print_flags(flags, "|", \
__def_vmaflag_names \
) : "none"
#ifdef CONFIG_COMPACTION
#define COMPACTION_STATUS \
EM( COMPACT_SKIPPED, "skipped") \
EM( COMPACT_DEFERRED, "deferred") \
EM( COMPACT_CONTINUE, "continue") \
EM( COMPACT_SUCCESS, "success") \
EM( COMPACT_PARTIAL_SKIPPED, "partial_skipped") \
EM( COMPACT_COMPLETE, "complete") \
EM( COMPACT_NO_SUITABLE_PAGE, "no_suitable_page") \
EM( COMPACT_NOT_SUITABLE_ZONE, "not_suitable_zone") \
EMe(COMPACT_CONTENDED, "contended")
/* High-level compaction status feedback */
#define COMPACTION_FAILED 1
#define COMPACTION_WITHDRAWN 2
#define COMPACTION_PROGRESS 3
#define compact_result_to_feedback(result) \
({ \
enum compact_result __result = result; \
(compaction_failed(__result)) ? COMPACTION_FAILED : \
(compaction_withdrawn(__result)) ? COMPACTION_WITHDRAWN : COMPACTION_PROGRESS; \
})
#define COMPACTION_FEEDBACK \
EM(COMPACTION_FAILED, "failed") \
EM(COMPACTION_WITHDRAWN, "withdrawn") \
EMe(COMPACTION_PROGRESS, "progress")
#define COMPACTION_PRIORITY \
EM(COMPACT_PRIO_SYNC_FULL, "COMPACT_PRIO_SYNC_FULL") \
EM(COMPACT_PRIO_SYNC_LIGHT, "COMPACT_PRIO_SYNC_LIGHT") \
EMe(COMPACT_PRIO_ASYNC, "COMPACT_PRIO_ASYNC")
#else
#define COMPACTION_STATUS
#define COMPACTION_PRIORITY
#define COMPACTION_FEEDBACK
#endif
#ifdef CONFIG_ZONE_DMA
#define IFDEF_ZONE_DMA(X) X
#else
#define IFDEF_ZONE_DMA(X)
#endif
#ifdef CONFIG_ZONE_DMA32
#define IFDEF_ZONE_DMA32(X) X
#else
#define IFDEF_ZONE_DMA32(X)
#endif
#ifdef CONFIG_HIGHMEM
#define IFDEF_ZONE_HIGHMEM(X) X
#else
#define IFDEF_ZONE_HIGHMEM(X)
#endif
#define ZONE_TYPE \
IFDEF_ZONE_DMA( EM (ZONE_DMA, "DMA")) \
IFDEF_ZONE_DMA32( EM (ZONE_DMA32, "DMA32")) \
EM (ZONE_NORMAL, "Normal") \
IFDEF_ZONE_HIGHMEM( EM (ZONE_HIGHMEM,"HighMem")) \
EMe(ZONE_MOVABLE,"Movable")
#define LRU_NAMES \
EM (LRU_INACTIVE_ANON, "inactive_anon") \
EM (LRU_ACTIVE_ANON, "active_anon") \
EM (LRU_INACTIVE_FILE, "inactive_file") \
EM (LRU_ACTIVE_FILE, "active_file") \
EMe(LRU_UNEVICTABLE, "unevictable")
/*
* First define the enums in the above macros to be exported to userspace
* via TRACE_DEFINE_ENUM().
*/
#undef EM
#undef EMe
#define EM(a, b) TRACE_DEFINE_ENUM(a);
#define EMe(a, b) TRACE_DEFINE_ENUM(a);
COMPACTION_STATUS
COMPACTION_PRIORITY
/* COMPACTION_FEEDBACK are defines not enums. Not needed here. */
ZONE_TYPE
LRU_NAMES
/*
* Now redefine the EM() and EMe() macros to map the enums to the strings
* that will be printed in the output.
*/
#undef EM
#undef EMe
#define EM(a, b) {a, b},
#define EMe(a, b) {a, b}
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