Check for a NULL cpumask_var_t when kicking multiple vCPUs via
cpumask_available(), which performs a !NULL check if and only if cpumasks
are configured to be allocated off-stack. This is a meaningless
optimization, e.g. avoids a TEST+Jcc and TEST+CMOV on x86, but more
importantly helps document that the NULL check is necessary even though
all callers pass in a local variable.
No functional change intended.
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210827092516.1027264-3-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Fix a benign data race reported by syzbot+KCSAN[*] by ensuring vcpu->cpu
is read exactly once, and by ensuring the vCPU is booted from guest mode
if kvm_arch_vcpu_should_kick() returns true. Fix a similar race in
kvm_make_vcpus_request_mask() by ensuring the vCPU is interrupted if
kvm_request_needs_ipi() returns true.
Reading vcpu->cpu before vcpu->mode (via kvm_arch_vcpu_should_kick() or
kvm_request_needs_ipi()) means the target vCPU could get migrated (change
vcpu->cpu) and enter !OUTSIDE_GUEST_MODE between reading vcpu->cpud and
reading vcpu->mode. If that happens, the kick/IPI will be sent to the
old pCPU, not the new pCPU that is now running the vCPU or reading SPTEs.
Although failing to kick the vCPU is not exactly ideal, practically
speaking it cannot cause a functional issue unless there is also a bug in
the caller, and any such bug would exist regardless of kvm_vcpu_kick()'s
behavior.
The purpose of sending an IPI is purely to get a vCPU into the host (or
out of reading SPTEs) so that the vCPU can recognize a change in state,
e.g. a KVM_REQ_* request. If vCPU's handling of the state change is
required for correctness, KVM must ensure either the vCPU sees the change
before entering the guest, or that the sender sees the vCPU as running in
guest mode. All architectures handle this by (a) sending the request
before calling kvm_vcpu_kick() and (b) checking for requests _after_
setting vcpu->mode.
x86's READING_SHADOW_PAGE_TABLES has similar requirements; KVM needs to
ensure it kicks and waits for vCPUs that started reading SPTEs _before_
MMU changes were finalized, but any vCPU that starts reading after MMU
changes were finalized will see the new state and can continue on
uninterrupted.
For uses of kvm_vcpu_kick() that are not paired with a KVM_REQ_*, e.g.
x86's kvm_arch_sync_dirty_log(), the order of the kick must not be relied
upon for functional correctness, e.g. in the dirty log case, userspace
cannot assume it has a 100% complete log if vCPUs are still running.
All that said, eliminate the benign race since the cost of doing so is an
"extra" atomic cmpxchg() in the case where the target vCPU is loaded by
the current pCPU or is not loaded at all. I.e. the kick will be skipped
due to kvm_vcpu_exiting_guest_mode() seeing a compatible vcpu->mode as
opposed to the kick being skipped because of the cpu checks.
Keep the "cpu != me" checks even though they appear useless/impossible at
first glance. x86 processes guest IPI writes in a fast path that runs in
IN_GUEST_MODE, i.e. can call kvm_vcpu_kick() from IN_GUEST_MODE. And
calling kvm_vm_bugged()->kvm_make_vcpus_request_mask() from IN_GUEST or
READING_SHADOW_PAGE_TABLES is perfectly reasonable.
Note, a race with the cpu_online() check in kvm_vcpu_kick() likely
persists, e.g. the vCPU could exit guest mode and get offlined between
the cpu_online() check and the sending of smp_send_reschedule(). But,
the online check appears to exist only to avoid a WARN in x86's
native_smp_send_reschedule() that fires if the target CPU is not online.
The reschedule WARN exists because CPU offlining takes the CPU out of the
scheduling pool, i.e. the WARN is intended to detect the case where the
kernel attempts to schedule a task on an offline CPU. The actual sending
of the IPI is a non-issue as at worst it will simpy be dropped on the
floor. In other words, KVM's usurping of the reschedule IPI could
theoretically trigger a WARN if the stars align, but there will be no
loss of functionality.
[*] https://syzkaller.appspot.com/bug?extid=cd4154e502f43f10808a
Cc: Venkatesh Srinivas <venkateshs@google.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Fixes: 97222cc831 ("KVM: Emulate local APIC in kernel")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210827092516.1027264-2-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
grow_halt_poll_ns() ignores values between 0 and
halt_poll_ns_grow_start (10000 by default). However,
when we shrink halt_poll_ns we may fall way below
halt_poll_ns_grow_start and endup with halt_poll_ns
values that don't make a lot of sense: like 1 or 9,
or 19.
VCPU1 trace (halt_poll_ns_shrink equals 2):
VCPU1 grow 10000
VCPU1 shrink 5000
VCPU1 shrink 2500
VCPU1 shrink 1250
VCPU1 shrink 625
VCPU1 shrink 312
VCPU1 shrink 156
VCPU1 shrink 78
VCPU1 shrink 39
VCPU1 shrink 19
VCPU1 shrink 9
VCPU1 shrink 4
Mirror what grow_halt_poll_ns() does and set halt_poll_ns
to 0 as soon as new shrink-ed halt_poll_ns value falls
below halt_poll_ns_grow_start.
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210902031100.252080-1-senozhatsky@chromium.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
KVM/arm64 updates for 5.15
- Page ownership tracking between host EL1 and EL2
- Rely on userspace page tables to create large stage-2 mappings
- Fix incompatibility between pKVM and kmemleak
- Fix the PMU reset state, and improve the performance of the virtual PMU
- Move over to the generic KVM entry code
- Address PSCI reset issues w.r.t. save/restore
- Preliminary rework for the upcoming pKVM fixed feature
- A bunch of MM cleanups
- a vGIC fix for timer spurious interrupts
- Various cleanups
Add a new stat that counts the number of times a remote TLB flush is
requested, regardless of whether it kicks vCPUs out of guest mode. This
allows us to look at how often flushes are initiated.
Unlike remote_tlb_flush, this one applies to ARM's instruction-set-based
TLB flush implementation, so apply it there too.
Original-by: David Matlack <dmatlack@google.com>
Signed-off-by: Jing Zhang <jingzhangos@google.com>
Message-Id: <20210817002639.3856694-1-jingzhangos@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Don't export KVM's MMU notifier count helpers, under no circumstance
should any downstream module, including x86's vendor code, have a
legitimate reason to piggyback KVM's MMU notifier logic. E.g in the x86
case, only KVM's MMU should be elevating the notifier count, and that
code is always built into the core kvm.ko module.
Fixes: edb298c663 ("KVM: x86/mmu: bump mmu notifier count in kvm_zap_gfn_range")
Cc: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210902175951.1387989-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Add three log histogram stats to record the distribution of time spent
on successful polling, failed polling and VCPU wait.
halt_poll_success_hist: Distribution of spent time for a successful poll.
halt_poll_fail_hist: Distribution of spent time for a failed poll.
halt_wait_hist: Distribution of time a VCPU has spent on waiting.
Signed-off-by: Jing Zhang <jingzhangos@google.com>
Message-Id: <20210802165633.1866976-6-jingzhangos@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Allow archs to create arch-specific nodes under kvm->debugfs_dentry directory
besides the stats fields. The new interface kvm_arch_create_vm_debugfs() is
defined but not yet used. It's called after kvm->debugfs_dentry is created, so
it can be referenced directly in kvm_arch_create_vm_debugfs(). Arch should
define their own versions when they want to create extra debugfs nodes.
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20210730220455.26054-2-peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
These stores are copied and pasted from the "if" statements above.
They are dead and while they are not really a bug, they can be
confusing to anyone reading the code as well. Remove them.
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The memslot for a given gfn is looked up multiple times during page
fault handling. Avoid binary searching for it multiple times by caching
the most recently used slot. There is an existing VM-wide last_used_slot
but that does not work well for cases where vCPUs are accessing memory
in different slots (see performance data below).
Another benefit of caching the most recently use slot (versus looking
up the slot once and passing around a pointer) is speeding up memslot
lookups *across* faults and during spte prefetching.
To measure the performance of this change I ran dirty_log_perf_test with
64 vCPUs and 64 memslots and measured "Populate memory time" and
"Iteration 2 dirty memory time". Tests were ran with eptad=N to force
dirty logging to use fast_page_fault so its performance could be
measured.
Config | Metric | Before | After
---------- | ----------------------------- | ------ | ------
tdp_mmu=Y | Populate memory time | 6.76s | 5.47s
tdp_mmu=Y | Iteration 2 dirty memory time | 2.83s | 0.31s
tdp_mmu=N | Populate memory time | 20.4s | 18.7s
tdp_mmu=N | Iteration 2 dirty memory time | 2.65s | 0.30s
The "Iteration 2 dirty memory time" results are especially compelling
because they are equivalent to running the same test with a single
memslot. In other words, fast_page_fault performance no longer scales
with the number of memslots.
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20210804222844.1419481-4-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
lru_slot is used to keep track of the index of the most-recently used
memslot. The correct acronym would be "mru" but that is not a common
acronym. So call it last_used_slot which is a bit more obvious.
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20210804222844.1419481-2-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
KVM creates a debugfs directory for each VM in order to store statistics
about the virtual machine. The directory name is built from the process
pid and a VM fd. While generally unique, it is possible to keep a
file descriptor alive in a way that causes duplicate directories, which
manifests as these messages:
[ 471.846235] debugfs: Directory '20245-4' with parent 'kvm' already present!
Even though this should not happen in practice, it is more or less
expected in the case of KVM for testcases that call KVM_CREATE_VM and
close the resulting file descriptor repeatedly and in parallel.
When this happens, debugfs_create_dir() returns an error but
kvm_create_vm_debugfs() goes on to allocate stat data structs which are
later leaked. The slow memory leak was spotted by syzkaller, where it
caused OOM reports.
Since the issue only affects debugfs, do a lookup before calling
debugfs_create_dir, so that the message is downgraded and rate-limited.
While at it, ensure kvm->debugfs_dentry is NULL rather than an error
if it is not created. This fixes kvm_destroy_vm_debugfs, which was not
checking IS_ERR_OR_NULL correctly.
Cc: stable@vger.kernel.org
Fixes: 536a6f88c4 ("KVM: Create debugfs dir and stat files for each VM")
Reported-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Avoid taking mmu_lock for .invalidate_range_{start,end}() notifications
that are unrelated to KVM. This is possible now that memslot updates are
blocked from range_start() to range_end(); that ensures that lock elision
happens in both or none, and therefore that mmu_notifier_count updates
(which must occur while holding mmu_lock for write) are always paired
across start->end.
Based on patches originally written by Ben Gardon.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
We would like to avoid taking mmu_lock for .invalidate_range_{start,end}()
notifications that are unrelated to KVM. Because mmu_notifier_count
must be modified while holding mmu_lock for write, and must always
be paired across start->end to stay balanced, lock elision must
happen in both or none. Therefore, in preparation for this change,
this patch prevents memslot updates across range_start() and range_end().
Note, technically flag-only memslot updates could be allowed in parallel,
but stalling a memslot update for a relatively short amount of time is
not a scalability issue, and this is all more than complex enough.
A long note on the locking: a previous version of the patch used an rwsem
to block the memslot update while the MMU notifier run, but this resulted
in the following deadlock involving the pseudo-lock tagged as
"mmu_notifier_invalidate_range_start".
======================================================
WARNING: possible circular locking dependency detected
5.12.0-rc3+ #6 Tainted: G OE
------------------------------------------------------
qemu-system-x86/3069 is trying to acquire lock:
ffffffff9c775ca0 (mmu_notifier_invalidate_range_start){+.+.}-{0:0}, at: __mmu_notifier_invalidate_range_end+0x5/0x190
but task is already holding lock:
ffffaff7410a9160 (&kvm->mmu_notifier_slots_lock){.+.+}-{3:3}, at: kvm_mmu_notifier_invalidate_range_start+0x36d/0x4f0 [kvm]
which lock already depends on the new lock.
This corresponds to the following MMU notifier logic:
invalidate_range_start
take pseudo lock
down_read() (*)
release pseudo lock
invalidate_range_end
take pseudo lock (**)
up_read()
release pseudo lock
At point (*) we take the mmu_notifiers_slots_lock inside the pseudo lock;
at point (**) we take the pseudo lock inside the mmu_notifiers_slots_lock.
This could cause a deadlock (ignoring for a second that the pseudo lock
is not a lock):
- invalidate_range_start waits on down_read(), because the rwsem is
held by install_new_memslots
- install_new_memslots waits on down_write(), because the rwsem is
held till (another) invalidate_range_end finishes
- invalidate_range_end sits waits on the pseudo lock, held by
invalidate_range_start.
Removing the fairness of the rwsem breaks the cycle (in lockdep terms,
it would change the *shared* rwsem readers into *shared recursive*
readers), so open-code the wait using a readers count and a
spinlock. This also allows handling blockable and non-blockable
critical section in the same way.
Losing the rwsem fairness does theoretically allow MMU notifiers to
block install_new_memslots forever. Note that mm/mmu_notifier.c's own
retry scheme in mmu_interval_read_begin also uses wait/wake_up
and is likewise not fair.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Introduce this safe version of kvm_get_kvm() so that it can be called even
during vm destruction. Use it in kvm_debugfs_open() and remove the verbose
comment. Prepare to be used elsewhere.
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20210625153214.43106-3-peterx@redhat.com>
[Preserve the comment in kvm_debugfs_open. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The arguments to the KVM_CLEAR_DIRTY_LOG ioctl include a pointer,
therefore it needs a compat ioctl implementation. Otherwise,
32-bit userspace fails to invoke it on 64-bit kernels; for x86
it might work fine by chance if the padding is zero, but not
on big-endian architectures.
Reported-by: Thomas Sattler
Cc: stable@vger.kernel.org
Fixes: 2a31b9db15 ("kvm: introduce manual dirty log reprotect")
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
SMT siblings share caches and other hardware, and busy halt polling
will degrade its sibling performance if its sibling is working
Sean Christopherson suggested as below:
"Rather than disallowing halt-polling entirely, on x86 it should be
sufficient to simply have the hardware thread yield to its sibling(s)
via PAUSE. It probably won't get back all performance, but I would
expect it to be close.
This compiles on all KVM architectures, and AFAICT the intended usage
of cpu_relax() is identical for all architectures."
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Message-Id: <20210727111247.55510-1-lirongqing@baidu.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Lai Jiangshan
Sean Christopherson
Sergey Senozhatsky
Peter Xu
Paolo Bonzini
Jing Zhang
Maxim Levitsky
David Matlack
Sean Christopherson
Marc Zyngier
Li RongQing