The VM_ALLOW_ANY_UNCACHED flag is implemented for ARM64,
allowing KVM stage 2 device mapping attributes to use Normal-NC
rather than DEVICE_nGnRE, which allows guest mappings supporting
write-combining attributes (WC). ARM does not architecturally
guarantee this is safe, and indeed some MMIO regions like the GICv2
VCPU interface can trigger uncontained faults if Normal-NC is used.
To safely use VFIO in KVM the platform must guarantee full safety
in the guest where no action taken against a MMIO mapping can
trigger an uncontained failure. The expectation is that most VFIO PCI
platforms support this for both mapping types, at least in common
flows, based on some expectations of how PCI IP is integrated. So
make vfio-pci set the VM_ALLOW_ANY_UNCACHED flag.
Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Jason Gunthorpe <jgg@nvidia.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
Link: https://lore.kernel.org/r/20240224150546.368-5-ankita@nvidia.com
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
To provide VM with the ability to get device IO memory with NormalNC
property, map device MMIO in KVM for ARM64 at stage2 as NormalNC.
Having NormalNC S2 default puts guests in control (based on [1],
"Combining stage 1 and stage 2 memory type attributes") of device
MMIO regions memory mappings. The rules are summarized below:
([(S1) - stage1], [(S2) - stage 2])
S1 | S2 | Result
NORMAL-WB | NORMAL-NC | NORMAL-NC
NORMAL-WT | NORMAL-NC | NORMAL-NC
NORMAL-NC | NORMAL-NC | NORMAL-NC
DEVICE<attr> | NORMAL-NC | DEVICE<attr>
Still this cannot be generalized to non PCI devices such as GICv2.
There is insufficient information and uncertainity in the behavior
of non PCI driver. A driver must indicate support using the
new flag VM_ALLOW_ANY_UNCACHED.
Adapt KVM to make use of the flag VM_ALLOW_ANY_UNCACHED as indicator to
activate the S2 setting to NormalNc.
[1] section D8.5.5 of DDI0487J_a_a-profile_architecture_reference_manual.pdf
Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
Link: https://lore.kernel.org/r/20240224150546.368-4-ankita@nvidia.com
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
The VM_ALLOW_ANY_UNCACHED flag is implemented for ARM64, allowing KVM
stage 2 device mapping attributes to use NormalNC rather than
DEVICE_nGnRE, which allows guest mappings supporting write-combining
attributes (WC). ARM does not architecturally guarantee this is safe,
and indeed some MMIO regions like the GICv2 VCPU interface can trigger
uncontained faults if NormalNC is used.
Even worse, the expectation is that there are platforms where even
DEVICE_nGnRE can allow uncontained faults in corner cases. Unfortunately
existing ARM IP requires platform integration to take responsibility to
prevent this.
To safely use VFIO in KVM the platform must guarantee full safety in the
guest where no action taken against a MMIO mapping can trigger an
uncontained failure. The assumption is that most VFIO PCI platforms
support this for both mapping types, at least in common flows, based
on some expectations of how PCI IP is integrated. This can be enabled
more broadly, for instance into vfio-platform drivers, but only after
the platform vendor completes auditing for safety.
The VMA flag VM_ALLOW_ANY_UNCACHED was found to be the simplest and
cleanest way to communicate the information from VFIO to KVM that
mapping the region in S2 as NormalNC is safe. KVM consumes it to
activate the code that does the S2 mapping as NormalNC.
Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
Link: https://lore.kernel.org/r/20240224150546.368-3-ankita@nvidia.com
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Currently, KVM for ARM64 maps at stage 2 memory that is considered device
(i.e. it is not RAM) with DEVICE_nGnRE memory attributes; this setting
overrides (as per the ARM architecture [1]) any device MMIO mapping
present at stage 1, resulting in a set-up whereby a guest operating
system cannot determine device MMIO mapping memory attributes on its
own but it is always overridden by the KVM stage 2 default.
This set-up does not allow guest operating systems to select device
memory attributes independently from KVM stage-2 mappings
(refer to [1], "Combining stage 1 and stage 2 memory type attributes"),
which turns out to be an issue in that guest operating systems
(e.g. Linux) may request to map devices MMIO regions with memory
attributes that guarantee better performance (e.g. gathering
attribute - that for some devices can generate larger PCIe memory
writes TLPs) and specific operations (e.g. unaligned transactions)
such as the NormalNC memory type.
The default device stage 2 mapping was chosen in KVM for ARM64 since
it was considered safer (i.e. it would not allow guests to trigger
uncontained failures ultimately crashing the machine) but this
turned out to be asynchronous (SError) defeating the purpose.
Failures containability is a property of the platform and is independent
from the memory type used for MMIO device memory mappings.
Actually, DEVICE_nGnRE memory type is even more problematic than
Normal-NC memory type in terms of faults containability in that e.g.
aborts triggered on DEVICE_nGnRE loads cannot be made, architecturally,
synchronous (i.e. that would imply that the processor should issue at
most 1 load transaction at a time - it cannot pipeline them - otherwise
the synchronous abort semantics would break the no-speculation attribute
attached to DEVICE_XXX memory).
This means that regardless of the combined stage1+stage2 mappings a
platform is safe if and only if device transactions cannot trigger
uncontained failures and that in turn relies on platform capabilities
and the device type being assigned (i.e. PCIe AER/DPC error containment
and RAS architecture[3]); therefore the default KVM device stage 2
memory attributes play no role in making device assignment safer
for a given platform (if the platform design adheres to design
guidelines outlined in [3]) and therefore can be relaxed.
For all these reasons, relax the KVM stage 2 device memory attributes
from DEVICE_nGnRE to Normal-NC.
The NormalNC was chosen over a different Normal memory type default
at stage-2 (e.g. Normal Write-through) to avoid cache allocation/snooping.
Relaxing S2 KVM device MMIO mappings to Normal-NC is not expected to
trigger any issue on guest device reclaim use cases either (i.e. device
MMIO unmap followed by a device reset) at least for PCIe devices, in that
in PCIe a device reset is architected and carried out through PCI config
space transactions that are naturally ordered with respect to MMIO
transactions according to the PCI ordering rules.
Having Normal-NC S2 default puts guests in control (thanks to
stage1+stage2 combined memory attributes rules [1]) of device MMIO
regions memory mappings, according to the rules described in [1]
and summarized here ([(S1) - stage1], [(S2) - stage 2]):
S1 | S2 | Result
NORMAL-WB | NORMAL-NC | NORMAL-NC
NORMAL-WT | NORMAL-NC | NORMAL-NC
NORMAL-NC | NORMAL-NC | NORMAL-NC
DEVICE<attr> | NORMAL-NC | DEVICE<attr>
It is worth noting that currently, to map devices MMIO space to user
space in a device pass-through use case the VFIO framework applies memory
attributes derived from pgprot_noncached() settings applied to VMAs, which
result in device-nGnRnE memory attributes for the stage-1 VMM mappings.
This means that a userspace mapping for device MMIO space carried
out with the current VFIO framework and a guest OS mapping for the same
MMIO space may result in a mismatched alias as described in [2].
Defaulting KVM device stage-2 mappings to Normal-NC attributes does not
change anything in this respect, in that the mismatched aliases would
only affect (refer to [2] for a detailed explanation) ordering between
the userspace and GuestOS mappings resulting stream of transactions
(i.e. it does not cause loss of property for either stream of
transactions on its own), which is harmless given that the userspace
and GuestOS access to the device is carried out through independent
transactions streams.
A Normal-NC flag is not present today. So add a new kvm_pgtable_prot
(KVM_PGTABLE_PROT_NORMAL_NC) flag for it, along with its
corresponding PTE value 0x5 (0b101) determined from [1].
Lastly, adapt the stage2 PTE property setter function
(stage2_set_prot_attr) to handle the NormalNC attribute.
The entire discussion leading to this patch series may be followed through
the following links.
Link: https://lore.kernel.org/all/20230907181459.18145-3-ankita@nvidia.com
Link: https://lore.kernel.org/r/20231205033015.10044-1-ankita@nvidia.com
[1] section D8.5.5 - DDI0487J_a_a-profile_architecture_reference_manual.pdf
[2] section B2.8 - DDI0487J_a_a-profile_architecture_reference_manual.pdf
[3] sections 1.7.7.3/1.8.5.2/appendix C - DEN0029H_SBSA_7.1.pdf
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Will Deacon <will@kernel.org>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
Link: https://lore.kernel.org/r/20240224150546.368-2-ankita@nvidia.com
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Pull more bcachefs updates from Kent Overstreet:
"Some fixes, Some refactoring, some minor features:
- Assorted prep work for disk space accounting rewrite
- BTREE_TRIGGER_ATOMIC: after combining our trigger callbacks, this
makes our trigger context more explicit
- A few fixes to avoid excessive transaction restarts on
multithreaded workloads: fstests (in addition to ktest tests) are
now checking slowpath counters, and that's shaking out a few bugs
- Assorted tracepoint improvements
- Starting to break up bcachefs_format.h and move on disk types so
they're with the code they belong to; this will make room to start
documenting the on disk format better.
- A few minor fixes"
* tag 'bcachefs-2024-01-21' of https://evilpiepirate.org/git/bcachefs: (46 commits)
bcachefs: Improve inode_to_text()
bcachefs: logged_ops_format.h
bcachefs: reflink_format.h
bcachefs; extents_format.h
bcachefs: ec_format.h
bcachefs: subvolume_format.h
bcachefs: snapshot_format.h
bcachefs: alloc_background_format.h
bcachefs: xattr_format.h
bcachefs: dirent_format.h
bcachefs: inode_format.h
bcachefs; quota_format.h
bcachefs: sb-counters_format.h
bcachefs: counters.c -> sb-counters.c
bcachefs: comment bch_subvolume
bcachefs: bch_snapshot::btime
bcachefs: add missing __GFP_NOWARN
bcachefs: opts->compression can now also be applied in the background
bcachefs: Prep work for variable size btree node buffers
bcachefs: grab s_umount only if snapshotting
...
Pull timer updates from Thomas Gleixner:
"Updates for time and clocksources:
- A fix for the idle and iowait time accounting vs CPU hotplug.
The time is reset on CPU hotplug which makes the accumulated
systemwide time jump backwards.
- Assorted fixes and improvements for clocksource/event drivers"
* tag 'timers-core-2024-01-21' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
tick-sched: Fix idle and iowait sleeptime accounting vs CPU hotplug
clocksource/drivers/ep93xx: Fix error handling during probe
clocksource/drivers/cadence-ttc: Fix some kernel-doc warnings
clocksource/drivers/timer-ti-dm: Fix make W=n kerneldoc warnings
clocksource/timer-riscv: Add riscv_clock_shutdown callback
dt-bindings: timer: Add StarFive JH8100 clint
dt-bindings: timer: thead,c900-aclint-mtimer: separate mtime and mtimecmp regs
Pull powerpc fixes from Aneesh Kumar:
- Increase default stack size to 32KB for Book3S
Thanks to Michael Ellerman.
* tag 'powerpc-6.8-2' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux:
powerpc/64s: Increase default stack size to 32KB
Add a field to bch_snapshot for creation time; this will be important
when we start exposing the snapshot tree to userspace.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
The "apply this compression method in the background" paths now use the
compression option if background_compression is not set; this means that
setting or changing the compression option will cause existing data to
be compressed accordingly in the background.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
bcachefs btree nodes are big - typically 256k - and btree roots are
pinned in memory. As we're now up to 18 btrees, we now have significant
memory overhead in mostly empty btree roots.
And in the future we're going to start enforcing that certain btree node
boundaries exist, to solve lock contention issues - analagous to XFS's
AGIs.
Thus, we need to start allocating smaller btree node buffers when we
can. This patch changes code that refers to the filesystem constant
c->opts.btree_node_size to refer to the btree node buffer size -
btree_buf_bytes() - where appropriate.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
The variable tmp is being assigned a value but it isn't being
read afterwards. The assignment is redundant and so tmp can be
removed.
Cleans up clang scan build warning:
warning: Although the value stored to 'ret' is used in the enclosing
expression, the value is never actually read from 'ret'
[deadcode.DeadStores]
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
drop_locks_do() should not be used in a fastpath without first trying
the do in nonblocking mode - the unlock and relock will cause excessive
transaction restarts and potentially livelocking with other threads that
are contending for the same locks.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Factor out bch2_journal_bufs_to_text(), and use it in the
journal_entry_full() tracepoint; when we can't get a journal reservation
we need to know the outstanding journal entry sizes to know if the
problem is due to excessive flushing.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
When issuing discards, we may need to flush the journal if there's too
many buckets that can't be discarded until a journal flush.
But the heuristic was bad; we should be comparing the number of buckets
that need to flushes against the number of free buckets, not the number
of buckets we saw.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Also print out the data_opts, so that we can see what specifically is
being done to an extent.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This fixes a bug with rebalance IOs getting stuck with reads completed,
but writes never being issued.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Drop t he loop in bch2_kthread_io_clock_wait(): this allows the code
that uses it to be woken up for other reasons, and fixes a bug where
rebalance wouldn't wake up when a scan was requested.
This raises the possibility of spurious wakeups, but callers should
always be able to handle that reasonably well.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Pull header fix from Kent Overstreet:
"Just one small fixup for the RT build"
* tag 'header_cleanup-2024-01-20' of https://evilpiepirate.org/git/bcachefs:
spinlock: Fix failing build for PREEMPT_RT
We don't have to take locks in any particular ordering - we'll make
forward progress just fine - but if we try to stick to an ordering, it
can help to avoid excessive would_deadlock transaction restarts.
This tweaks the reflink path to take extents btree locks in the right
order.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
The disk space accounting rewrite is splitting out accounting for each
replicas set - those are moving to btree keys, instead of percpu
counters.
This breaks bch2_trans_fs_usage_apply() up, splitting out the part we
will still need.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Split out base filesystem usage into its own type; prep work for
breaking up bch2_trans_fs_usage_apply().
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
