The perf subsystem today unifies various tracing and monitoring
features, from both software and hardware. One benefit of the perf
subsystem is automatically inheriting events to child tasks, which
enables process-wide events monitoring with low overheads. By default
perf events are non-intrusive, not affecting behaviour of the tasks
being monitored.
For certain use-cases, however, it makes sense to leverage the
generality of the perf events subsystem and optionally allow the tasks
being monitored to receive signals on events they are interested in.
This patch series adds the option to synchronously signal user space on
events.
To better support process-wide synchronous self-monitoring, without
events propagating to children that do not share the current process's
shared environment, two pre-requisite patches are added to optionally
restrict inheritance to CLONE_THREAD, and remove events on exec (without
affecting the parent).
Examples how to use these features can be found in the tests added at
the end of the series. In addition to the tests added, the series has
also been subjected to syzkaller fuzzing (focus on 'kernel/events/'
coverage).
Motivation and Example Uses
---------------------------
1. Our immediate motivation is low-overhead sampling-based race
detection for user space [1]. By using perf_event_open() at
process initialization, we can create hardware
breakpoint/watchpoint events that are propagated automatically
to all threads in a process. As far as we are aware, today no
existing kernel facility (such as ptrace) allows us to set up
process-wide watchpoints with minimal overheads (that are
comparable to mprotect() of whole pages).
2. Other low-overhead error detectors that rely on detecting
accesses to certain memory locations or code, process-wide and
also only in a specific set of subtasks or threads.
[1] https://llvm.org/devmtg/2020-09/slides/Morehouse-GWP-Tsan.pdf
Other ideas for use-cases we found interesting, but should only
illustrate the range of potential to further motivate the utility (we're
sure there are more):
3. Code hot patching without full stop-the-world. Specifically, by
setting a code breakpoint to entry to the patched routine, then
send signals to threads and check that they are not in the
routine, but without stopping them further. If any of the
threads will enter the routine, it will receive SIGTRAP and
pause.
4. Safepoints without mprotect(). Some Java implementations use
"load from a known memory location" as a safepoint. When threads
need to be stopped, the page containing the location is
mprotect()ed and threads get a signal. This could be replaced with
a watchpoint, which does not require a whole page nor DTLB
shootdowns.
5. Threads receiving signals on performance events to
throttle/unthrottle themselves.
6. Tracking data flow globally.
Changelog
---------
v4:
* Fix for parent and child racing to exit in sync_child_event().
* Fix race between irq_work running and task's sighand being released by
release_task().
* Generalize setting si_perf and si_addr independent of event type;
introduces perf_event_attr::sig_data, which can be set by user space
to be propagated to si_perf.
* Warning in perf_sigtrap() if ctx->task and current mismatch; we expect
this on architectures that do not properly implement
arch_irq_work_raise().
* Require events that want sigtrap to be associated with a task.
* Dropped "perf: Add breakpoint information to siginfo on SIGTRAP"
in favor of more generic solution (perf_event_attr::sig_data).
v3:
* Add patch "perf: Rework perf_event_exit_event()" to beginning of
series, courtesy of Peter Zijlstra.
* Rework "perf: Add support for event removal on exec" based on
the added "perf: Rework perf_event_exit_event()".
* Fix kselftests to work with more recent libc, due to the way it forces
using the kernel's own siginfo_t.
* Add basic perf-tool built-in test.
v2/RFC: https://lkml.kernel.org/r/20210310104139.679618-1-elver@google.com
* Patch "Support only inheriting events if cloned with CLONE_THREAD"
added to series.
* Patch "Add support for event removal on exec" added to series.
* Patch "Add kselftest for process-wide sigtrap handling" added to
series.
* Patch "Add kselftest for remove_on_exec" added to series.
* Implicitly restrict inheriting events if sigtrap, but the child was
cloned with CLONE_CLEAR_SIGHAND, because it is not generally safe if
the child cleared all signal handlers to continue sending SIGTRAP.
* Various minor fixes (see details in patches).
v1/RFC: https://lkml.kernel.org/r/20210223143426.2412737-1-elver@google.com
Pre-series: The discussion at [2] led to the changes in this series. The
approach taken in "Add support for SIGTRAP on perf events" to trigger
the signal was suggested by Peter Zijlstra in [3].
[2] https://lore.kernel.org/lkml/CACT4Y+YPrXGw+AtESxAgPyZ84TYkNZdP0xpocX2jwVAbZ…
[3] https://lore.kernel.org/lkml/YBv3rAT566k+6zjg@hirez.programming.kicks-ass.n…
Marco Elver (9):
perf: Apply PERF_EVENT_IOC_MODIFY_ATTRIBUTES to children
perf: Support only inheriting events if cloned with CLONE_THREAD
perf: Add support for event removal on exec
signal: Introduce TRAP_PERF si_code and si_perf to siginfo
perf: Add support for SIGTRAP on perf events
selftests/perf_events: Add kselftest for process-wide sigtrap handling
selftests/perf_events: Add kselftest for remove_on_exec
tools headers uapi: Sync tools/include/uapi/linux/perf_event.h
perf test: Add basic stress test for sigtrap handling
Peter Zijlstra (1):
perf: Rework perf_event_exit_event()
arch/m68k/kernel/signal.c | 3 +
arch/x86/kernel/signal_compat.c | 5 +-
fs/signalfd.c | 4 +
include/linux/compat.h | 2 +
include/linux/perf_event.h | 9 +-
include/linux/signal.h | 1 +
include/uapi/asm-generic/siginfo.h | 6 +-
include/uapi/linux/perf_event.h | 12 +-
include/uapi/linux/signalfd.h | 4 +-
kernel/events/core.c | 302 +++++++++++++-----
kernel/fork.c | 2 +-
kernel/signal.c | 11 +
tools/include/uapi/linux/perf_event.h | 12 +-
tools/perf/tests/Build | 1 +
tools/perf/tests/builtin-test.c | 5 +
tools/perf/tests/sigtrap.c | 150 +++++++++
tools/perf/tests/tests.h | 1 +
.../testing/selftests/perf_events/.gitignore | 3 +
tools/testing/selftests/perf_events/Makefile | 6 +
tools/testing/selftests/perf_events/config | 1 +
.../selftests/perf_events/remove_on_exec.c | 260 +++++++++++++++
tools/testing/selftests/perf_events/settings | 1 +
.../selftests/perf_events/sigtrap_threads.c | 210 ++++++++++++
23 files changed, 924 insertions(+), 87 deletions(-)
create mode 100644 tools/perf/tests/sigtrap.c
create mode 100644 tools/testing/selftests/perf_events/.gitignore
create mode 100644 tools/testing/selftests/perf_events/Makefile
create mode 100644 tools/testing/selftests/perf_events/config
create mode 100644 tools/testing/selftests/perf_events/remove_on_exec.c
create mode 100644 tools/testing/selftests/perf_events/settings
create mode 100644 tools/testing/selftests/perf_events/sigtrap_threads.c
--
2.31.0.208.g409f899ff0-goog
Hi all,
following bug is trying to workaround an error on ppc64le, where
zram01.sh LTP test (there is also kernel selftest
tools/testing/selftests/zram/zram01.sh, but LTP test got further
updates) has often mem_used_total 0 although zram is already filled.
Patch tries to repeatedly read /sys/block/zram*/mm_stat for 1 sec,
waiting for mem_used_total > 0. The question if this is expected and
should be workarounded or a bug which should be fixed.
REPRODUCE THE ISSUE
Quickest way to install only zram tests and their dependencies:
make autotools && ./configure && for i in testcases/lib/ testcases/kernel/device-drivers/zram/; do cd $i && make -j$(getconf _NPROCESSORS_ONLN) && make install && cd -; done
Run the test (only on vfat)
PATH="/opt/ltp/testcases/bin:$PATH" LTP_SINGLE_FS_TYPE=vfat zram01.sh
Petr Vorel (1):
zram01.sh: Workaround division by 0 on vfat on ppc64le
.../kernel/device-drivers/zram/zram01.sh | 27 +++++++++++++++++--
1 file changed, 25 insertions(+), 2 deletions(-)
--
2.38.0
I checked and the Landlock ptrace test failed because Yama is enabled,
which is expected. You can check that with
/proc/sys/kernel/yama/ptrace_scope
Jeff Xu sent a patch to fix this case but it is not ready yet:
https://lore.kernel.org/r/20220628222941.2642917-1-jeffxu@google.com
Could you please send a new patch Jeff, and add Limin in Cc?
On 29/11/2022 12:26, limin wrote:
> cat /proc/cmdline
> BOOT_IMAGE=/vmlinuz-6.1.0-next-20221116
> root=UUID=a65b3a79-dc02-4728-8a0c-5cf24f4ae08b ro
> systemd.unified_cgroup_hierarchy=1 cgroup_no_v1=all
>
>
> config
>
> #
> # Automatically generated file; DO NOT EDIT.
> # Linux/x86 6.1.0-rc6 Kernel Configuration
> #
[...]
> CONFIG_SECURITY_YAMA=y
[...]
> CONFIG_LSM="landlock,lockdown,yama,integrity,apparmor"
[...]
>
> On 2022/11/29 19:03, Mickaël Salaün wrote:
>> I tested with next-20221116 and all tests are OK. Could you share your
>> kernel configuration with a link? What is the content of /proc/cmdline?
>>
>> On 29/11/2022 02:42, limin wrote:
>>> I run test on Linux ubuntu2204 6.1.0-next-20221116
>>>
>>> I did't use yama.
>>>
>>> you can reproduce by this step:
>>>
>>> cd kernel_src
>>>
>>> cd tools/testing/selftests/landlock/
>>> make
>>> ./ptrace_test
>>>
>>>
>>>
>>>
>>> On 2022/11/29 3:44, Mickaël Salaün wrote:
>>>> This patch changes the test semantic and then cannot work on my test
>>>> environment. On which kernel did you run test? Do you use Yama or
>>>> something similar?
>>>>
>>>> On 28/11/2022 03:04, limin wrote:
>>>>> Tests PTRACE_ATTACH and PTRACE_MODE_READ on the parent,
>>>>> trace parent return -1 when child== 0
>>>>> How to reproduce warning:
>>>>> $ make -C tools/testing/selftests TARGETS=landlock run_tests
>>>>>
>>>>> Signed-off-by: limin <limin100(a)huawei.com>
>>>>> ---
>>>>> tools/testing/selftests/landlock/ptrace_test.c | 5 ++---
>>>>> 1 file changed, 2 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/tools/testing/selftests/landlock/ptrace_test.c
>>>>> b/tools/testing/selftests/landlock/ptrace_test.c
>>>>> index c28ef98ff3ac..88c4dc63eea0 100644
>>>>> --- a/tools/testing/selftests/landlock/ptrace_test.c
>>>>> +++ b/tools/testing/selftests/landlock/ptrace_test.c
>>>>> @@ -267,12 +267,11 @@ TEST_F(hierarchy, trace)
>>>>> /* Tests PTRACE_ATTACH and PTRACE_MODE_READ on the
>>>>> parent. */
>>>>> err_proc_read = test_ptrace_read(parent);
>>>>> ret = ptrace(PTRACE_ATTACH, parent, NULL, 0);
>>>>> + EXPECT_EQ(-1, ret);
>>>>> + EXPECT_EQ(EPERM, errno);
>>>>> if (variant->domain_child) {
>>>>> - EXPECT_EQ(-1, ret);
>>>>> - EXPECT_EQ(EPERM, errno);
>>>>> EXPECT_EQ(EACCES, err_proc_read);
>>>>> } else {
>>>>> - EXPECT_EQ(0, ret);
>>>>> EXPECT_EQ(0, err_proc_read);
>>>>> }
>>>>> if (ret == 0) {
This is the v7 of this series which tries to implement the fd-based KVM
guest private memory. The patches are based on latest kvm/queue branch
commit:
b9b71f43683a (kvm/queue) KVM: x86/mmu: Buffer nested MMU
split_desc_cache only by default capacity
Introduction
------------
In general this patch series introduce fd-based memslot which provides
guest memory through memory file descriptor fd[offset,size] instead of
hva/size. The fd can be created from a supported memory filesystem
like tmpfs/hugetlbfs etc. which we refer as memory backing store. KVM
and the the memory backing store exchange callbacks when such memslot
gets created. At runtime KVM will call into callbacks provided by the
backing store to get the pfn with the fd+offset. Memory backing store
will also call into KVM callbacks when userspace punch hole on the fd
to notify KVM to unmap secondary MMU page table entries.
Comparing to existing hva-based memslot, this new type of memslot allows
guest memory unmapped from host userspace like QEMU and even the kernel
itself, therefore reduce attack surface and prevent bugs.
Based on this fd-based memslot, we can build guest private memory that
is going to be used in confidential computing environments such as Intel
TDX and AMD SEV. When supported, the memory backing store can provide
more enforcement on the fd and KVM can use a single memslot to hold both
the private and shared part of the guest memory.
mm extension
---------------------
Introduces new MFD_INACCESSIBLE flag for memfd_create(), the file
created with these flags cannot read(), write() or mmap() etc via normal
MMU operations. The file content can only be used with the newly
introduced memfile_notifier extension.
The memfile_notifier extension provides two sets of callbacks for KVM to
interact with the memory backing store:
- memfile_notifier_ops: callbacks for memory backing store to notify
KVM when memory gets invalidated.
- backing store callbacks: callbacks for KVM to call into memory
backing store to request memory pages for guest private memory.
The memfile_notifier extension also provides APIs for memory backing
store to register/unregister itself and to trigger the notifier when the
bookmarked memory gets invalidated.
The patchset also introduces a new memfd seal F_SEAL_AUTO_ALLOCATE to
prevent double allocation caused by unintentional guest when we only
have a single side of the shared/private memfds effective.
memslot extension
-----------------
Add the private fd and the fd offset to existing 'shared' memslot so
that both private/shared guest memory can live in one single memslot.
A page in the memslot is either private or shared. Whether a guest page
is private or shared is maintained through reusing existing SEV ioctls
KVM_MEMORY_ENCRYPT_{UN,}REG_REGION.
Test
----
To test the new functionalities of this patch TDX patchset is needed.
Since TDX patchset has not been merged so I did two kinds of test:
- Regresion test on kvm/queue (this patchset)
Most new code are not covered. Code also in below repo:
https://github.com/chao-p/linux/tree/privmem-v7
- New Funational test on latest TDX code
The patch is rebased to latest TDX code and tested the new
funcationalities. See below repos:
Linux: https://github.com/chao-p/linux/tree/privmem-v7-tdx
QEMU: https://github.com/chao-p/qemu/tree/privmem-v7
An example QEMU command line for TDX test:
-object tdx-guest,id=tdx,debug=off,sept-ve-disable=off \
-machine confidential-guest-support=tdx \
-object memory-backend-memfd-private,id=ram1,size=${mem} \
-machine memory-backend=ram1
Changelog
----------
v7:
- Move the private/shared info from backing store to KVM.
- Introduce F_SEAL_AUTO_ALLOCATE to avoid double allocation.
- Rework on the sync mechanism between zap/page fault paths.
- Addressed other comments in v6.
v6:
- Re-organzied patch for both mm/KVM parts.
- Added flags for memfile_notifier so its consumers can state their
features and memory backing store can check against these flags.
- Put a backing store reference in the memfile_notifier and move pfn_ops
into backing store.
- Only support boot time backing store register.
- Overall KVM part improvement suggested by Sean and some others.
v5:
- Removed userspace visible F_SEAL_INACCESSIBLE, instead using an
in-kernel flag (SHM_F_INACCESSIBLE for shmem). Private fd can only
be created by MFD_INACCESSIBLE.
- Introduced new APIs for backing store to register itself to
memfile_notifier instead of direct function call.
- Added the accounting and restriction for MFD_INACCESSIBLE memory.
- Added KVM API doc for new memslot extensions and man page for the new
MFD_INACCESSIBLE flag.
- Removed the overlap check for mapping the same file+offset into
multiple gfns due to perf consideration, warned in document.
- Addressed other comments in v4.
v4:
- Decoupled the callbacks between KVM/mm from memfd and use new
name 'memfile_notifier'.
- Supported register multiple memslots to the same backing store.
- Added per-memslot pfn_ops instead of per-system.
- Reworked the invalidation part.
- Improved new KVM uAPIs (private memslot extension and memory
error) per Sean's suggestions.
- Addressed many other minor fixes for comments from v3.
v3:
- Added locking protection when calling
invalidate_page_range/fallocate callbacks.
- Changed memslot structure to keep use useraddr for shared memory.
- Re-organized F_SEAL_INACCESSIBLE and MEMFD_OPS.
- Added MFD_INACCESSIBLE flag to force F_SEAL_INACCESSIBLE.
- Commit message improvement.
- Many small fixes for comments from the last version.
Links to previous discussions
-----------------------------
[1] Original design proposal:
https://lkml.kernel.org/kvm/20210824005248.200037-1-seanjc@google.com/
[2] Updated proposal and RFC patch v1:
https://lkml.kernel.org/linux-fsdevel/20211111141352.26311-1-chao.p.peng@li…
[3] Patch v5: https://lkml.org/lkml/2022/5/19/861
Chao Peng (12):
mm: Add F_SEAL_AUTO_ALLOCATE seal to memfd
selftests/memfd: Add tests for F_SEAL_AUTO_ALLOCATE
mm: Introduce memfile_notifier
mm/memfd: Introduce MFD_INACCESSIBLE flag
KVM: Rename KVM_PRIVATE_MEM_SLOTS to KVM_INTERNAL_MEM_SLOTS
KVM: Use gfn instead of hva for mmu_notifier_retry
KVM: Rename mmu_notifier_*
KVM: Extend the memslot to support fd-based private memory
KVM: Add KVM_EXIT_MEMORY_FAULT exit
KVM: Register/unregister the guest private memory regions
KVM: Handle page fault for private memory
KVM: Enable and expose KVM_MEM_PRIVATE
Kirill A. Shutemov (1):
mm/shmem: Support memfile_notifier
Documentation/virt/kvm/api.rst | 77 +++++-
arch/arm64/kvm/mmu.c | 8 +-
arch/mips/include/asm/kvm_host.h | 2 +-
arch/mips/kvm/mmu.c | 10 +-
arch/powerpc/include/asm/kvm_book3s_64.h | 2 +-
arch/powerpc/kvm/book3s_64_mmu_host.c | 4 +-
arch/powerpc/kvm/book3s_64_mmu_hv.c | 4 +-
arch/powerpc/kvm/book3s_64_mmu_radix.c | 6 +-
arch/powerpc/kvm/book3s_hv_nested.c | 2 +-
arch/powerpc/kvm/book3s_hv_rm_mmu.c | 8 +-
arch/powerpc/kvm/e500_mmu_host.c | 4 +-
arch/riscv/kvm/mmu.c | 4 +-
arch/x86/include/asm/kvm_host.h | 3 +-
arch/x86/kvm/Kconfig | 3 +
arch/x86/kvm/mmu.h | 2 -
arch/x86/kvm/mmu/mmu.c | 74 +++++-
arch/x86/kvm/mmu/mmu_internal.h | 18 ++
arch/x86/kvm/mmu/mmutrace.h | 1 +
arch/x86/kvm/mmu/paging_tmpl.h | 4 +-
arch/x86/kvm/x86.c | 2 +-
include/linux/kvm_host.h | 105 +++++---
include/linux/memfile_notifier.h | 91 +++++++
include/linux/shmem_fs.h | 2 +
include/uapi/linux/fcntl.h | 1 +
include/uapi/linux/kvm.h | 37 +++
include/uapi/linux/memfd.h | 1 +
mm/Kconfig | 4 +
mm/Makefile | 1 +
mm/memfd.c | 18 +-
mm/memfile_notifier.c | 123 ++++++++++
mm/shmem.c | 125 +++++++++-
tools/testing/selftests/memfd/memfd_test.c | 166 +++++++++++++
virt/kvm/Kconfig | 3 +
virt/kvm/kvm_main.c | 272 ++++++++++++++++++---
virt/kvm/pfncache.c | 14 +-
35 files changed, 1074 insertions(+), 127 deletions(-)
create mode 100644 include/linux/memfile_notifier.h
create mode 100644 mm/memfile_notifier.c
--
2.25.1