Until CONFIG_DMABUF_SYSFS_STATS was added [1] it was only possible to
perform per-buffer accounting with debugfs which is not suitable for
production environments. Eventually we discovered the overhead with
per-buffer sysfs file creation/removal was significantly impacting
allocation and free times, and exacerbated kernfs lock contention. [2]
dma_buf_stats_setup() is responsible for 39% of single-page buffer
creation duration, or 74% of single-page dma_buf_export() duration when
stressing dmabuf allocations and frees.
I prototyped a change from per-buffer to per-exporter statistics with a
RCU protected list of exporter allocations that accommodates most (but
not all) of our use-cases and avoids almost all of the sysfs overhead.
While that adds less overhead than per-buffer sysfs, and less even than
the maintenance of the dmabuf debugfs_list, it's still *additional*
overhead on top of the debugfs_list and doesn't give us per-buffer info.
This series uses the existing dmabuf debugfs_list to implement a BPF
dmabuf iterator, which adds no overhead to buffer allocation/free and
provides per-buffer info. The list has been moved outside of
CONFIG_DEBUG_FS scope so that it is always populated. The BPF program
loaded by userspace that extracts per-buffer information gets to define
its own interface which avoids the lack of ABI stability with debugfs.
This will allow us to replace our use of CONFIG_DMABUF_SYSFS_STATS, and
the plan is to remove it from the kernel after the next longterm stable
release.
[1] https://lore.kernel.org/linux-media/20201210044400.1080308-1-hridya@google.…
[2] https://lore.kernel.org/all/20220516171315.2400578-1-tjmercier@google.com
v1: https://lore.kernel.org/all/20250414225227.3642618-1-tjmercier@google.com
v1 -> v2:
Make the DMA buffer list independent of CONFIG_DEBUG_FS per Christian
König
Add CONFIG_DMA_SHARED_BUFFER check to kernel/bpf/Makefile per kernel
test robot
Use BTF_ID_LIST_SINGLE instead of BTF_ID_LIST_GLOBAL_SINGLE per Song Liu
Fixup comment style, mixing code/declarations, and use ASSERT_OK_FD in
selftest per Song Liu
Add BPF_ITER_RESCHED feature to bpf_dmabuf_reg_info per Alexei
Starovoitov
Add open-coded iterator and selftest per Alexei Starovoitov
Add a second test buffer from the system dmabuf heap to selftests
Use the BPF program we'll use in production for selftest per Alexei
Starovoitov
https://r.android.com/c/platform/system/bpfprogs/+/3616123/2/dmabufIter.chttps://r.android.com/c/platform/system/memory/libmeminfo/+/3614259/1/libdm…
v2: https://lore.kernel.org/all/20250504224149.1033867-1-tjmercier@google.com
v2 -> v3:
Rebase onto bpf-next/master
Move get_next_dmabuf() into drivers/dma-buf/dma-buf.c, along with the
new get_first_dmabuf(). This avoids having to expose the dmabuf list
and mutex to the rest of the kernel, and keeps the dmabuf mutex
operations near each other in the same file. (Christian König)
Add Christian's RB to dma-buf: Rename debugfs symbols
Drop RFC: dma-buf: Remove DMA-BUF statistics
v3: https://lore.kernel.org/all/20250507001036.2278781-1-tjmercier@google.com
v3 -> v4:
Fix selftest BPF program comment style (not kdoc) per Alexei Starovoitov
Fix dma-buf.c kdoc comment style per Alexei Starovoitov
Rename get_first_dmabuf / get_next_dmabuf to dma_buf_iter_begin /
dma_buf_iter_next per Christian König
Add Christian's RB to bpf: Add dmabuf iterator
v4: https://lore.kernel.org/all/20250508182025.2961555-1-tjmercier@google.com
v4 -> v5:
Add Christian's Acks to all patches
Add Song Liu's Acks
Move BTF_ID_LIST_SINGLE and DEFINE_BPF_ITER_FUNC closer to usage per
Song Liu
Fix open-coded iterator comment style per Song Liu
Move iterator termination check to its own subtest per Song Liu
Rework selftest buffer creation per Song Liu
Fix spacing in sanitize_string per BPF CI
v5: https://lore.kernel.org/all/20250512174036.266796-1-tjmercier@google.com
v5 -> v6:
Song Liu:
Init test buffer FDs to -1
Zero-init udmabuf_create for future proofing
Bail early for iterator fd/FILE creation failure
Dereference char ptr to check for NUL in sanitize_string()
Move map insertion from create_test_buffers() to test_dmabuf_iter()
Add ACK to selftests/bpf: Add test for open coded dmabuf_iter
T.J. Mercier (5):
dma-buf: Rename debugfs symbols
bpf: Add dmabuf iterator
bpf: Add open coded dmabuf iterator
selftests/bpf: Add test for dmabuf_iter
selftests/bpf: Add test for open coded dmabuf_iter
drivers/dma-buf/dma-buf.c | 98 ++++--
include/linux/dma-buf.h | 4 +-
kernel/bpf/Makefile | 3 +
kernel/bpf/dmabuf_iter.c | 150 +++++++++
kernel/bpf/helpers.c | 5 +
.../testing/selftests/bpf/bpf_experimental.h | 5 +
tools/testing/selftests/bpf/config | 3 +
.../selftests/bpf/prog_tests/dmabuf_iter.c | 285 ++++++++++++++++++
.../testing/selftests/bpf/progs/dmabuf_iter.c | 91 ++++++
9 files changed, 622 insertions(+), 22 deletions(-)
create mode 100644 kernel/bpf/dmabuf_iter.c
create mode 100644 tools/testing/selftests/bpf/prog_tests/dmabuf_iter.c
create mode 100644 tools/testing/selftests/bpf/progs/dmabuf_iter.c
base-commit: 43745d11bfd9683abdf08ad7a5cc403d6a9ffd15
--
2.49.0.1045.g170613ef41-goog
The kunit test that checks the longests symbol length [1], has triggered
warnings in some pilelines when symbol prefixes are used [2][3]. The test
will to depend on !PREFIX_SYMBOLS and !CFI_CLANG as sujested in [4] and
on !GCOV_KERNEL.
[1] https://lore.kernel.org/rust-for-linux/CABVgOSm=5Q0fM6neBhxSbOUHBgNzmwf2V22…
[2] https://lore.kernel.org/all/20250328112156.2614513-1-arnd@kernel.org/T/#u
[3] https://lore.kernel.org/rust-for-linux/bbd03b37-c4d9-4a92-9be2-75aaf8c19815…
[4] https://lore.kernel.org/linux-kselftest/20250427200916.GA1661412@ax162/T/#t
Reviewed-by: Rae Moar <rmoar(a)google.com>
Signed-off-by: Sergio González Collado <sergio.collado(a)gmail.com>
---
v2 -> v3: added dependency on !GCOV_KERNEL (to avoid __gcov_ prefix)
---
v1 -> v2: added dependency on !CFI_CLANG as suggested in [3], removed
CONFIG_ prefix
---
lib/Kconfig.debug | 1 +
lib/tests/longest_symbol_kunit.c | 3 +--
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index f9051ab610d5..e55c761eae20 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2886,6 +2886,7 @@ config FORTIFY_KUNIT_TEST
config LONGEST_SYM_KUNIT_TEST
tristate "Test the longest symbol possible" if !KUNIT_ALL_TESTS
depends on KUNIT && KPROBES
+ depends on !PREFIX_SYMBOLS && !CFI_CLANG && !GCOV_KERNEL
default KUNIT_ALL_TESTS
help
Tests the longest symbol possible
diff --git a/lib/tests/longest_symbol_kunit.c b/lib/tests/longest_symbol_kunit.c
index e3c28ff1807f..9b4de3050ba7 100644
--- a/lib/tests/longest_symbol_kunit.c
+++ b/lib/tests/longest_symbol_kunit.c
@@ -3,8 +3,7 @@
* Test the longest symbol length. Execute with:
* ./tools/testing/kunit/kunit.py run longest-symbol
* --arch=x86_64 --kconfig_add CONFIG_KPROBES=y --kconfig_add CONFIG_MODULES=y
- * --kconfig_add CONFIG_RETPOLINE=n --kconfig_add CONFIG_CFI_CLANG=n
- * --kconfig_add CONFIG_MITIGATION_RETPOLINE=n
+ * --kconfig_add CONFIG_CPU_MITIGATIONS=n --kconfig_add CONFIG_GCOV_KERNEL=n
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
base-commit: 1a80a098c606b285fb0a13aa992af4f86da1ff06
--
2.39.2
From: Chia-Yu Chang <chia-yu.chang(a)nokia-bell-labs.com>
Hello,
Please find the v6:
v5 (09-May-2025)
- Add #3 to utilize exisintg holes of tcp_sock_write_txrx group for later patches (#4, #9, #10) with new u8 members (Paolo Abeni <pabeni(a)redhat.com>)
- Add pahole outcomes before and after commit in #4, #5, #6, #9, #10, #15 (Paolo Abeni <pabeni(a)redhat.com>)
- Define new helper function tcp_send_ack_reflect_ect() for sending ACK with reflected ECT in #5 (Paolo Abeni <pabeni(a)redhat.com>)
- Add comments for function tcp_ecn_rcv_synack() in #5 (Paolo Abeni <pabeni(a)redhat.com>)
- Add enum/define to be used by sysctl_tcp_ecn in #5, sysctl_tcp_ecn_option in #9, and sysctl_tcp_ecn_option_beacon in #10 (Paolo Abeni <pabeni(a)redhat.com>)
- Move accecn_fail_mode and saw_accecn_opt in #5 and #11 to use exisintg holes of tcp_sock (Paolo Abeni <pabeni(a)redhat.com>)
- Change data type of new members of tcp_request_sock and move them to the end of struct in #5 and #11 (Paolo Abeni <pabeni(a)redhat.com>)
- Move new members of tcp_info to the end of struct in #6 (Paolo Abeni <pabeni(a)redhat.com>)
- Merge previous #7 into #9 (Paolo Abeni <pabeni(a)redhat.com>)
- Mask ecnfield with INET_ECN_MASK to remove WARN_ONCE in #9 (Paolo Abeni <pabeni(a)redhat.com>)
- Reduce the indentation levels for reabability in #9 and #10 (Paolo Abeni <pabeni(a)redhat.com>)
- Move delivered_ecn_bytes to the RX group in #9, accecn_opt_tstamp to the TX group in #10, pkts_acked_ewma to the RX group in #15 (Paolo Abeni <pabeni(a)redhat.com>)
- Add changes in Documentation/networking/net_cachelines/tcp_sock.rst for new tcp_sock members in #3, #5, #6, #9, #10, #15
v5 (22-Apr-2025)
- Further fix for 32-bit ARM alignment in tcp.c (Simon Horman <horms(a)kernel.org>)
v4 (18-Apr-2025)
- Fix 32-bit ARM assertion for alignment requirement (Simon Horman <horms(a)kernel.org>)
v3 (14-Apr-2025)
- Fix patch apply issue in v2 (Jakub Kicinski <kuba(a)kernel.org>)
v2 (18-Mar-2025)
- Add one missing patch from the previous AccECN protocol preparation patch series to this patch series.
The full patch series can be found in
https://github.com/L4STeam/linux-net-next/commits/upstream_l4steam/
The Accurate ECN draft can be found in
https://datatracker.ietf.org/doc/html/draft-ietf-tcpm-accurate-ecn-28
Best regards,
Chia-Yu
Chia-Yu Chang (2):
tcp: reorganize tcp_sock_write_txrx group for variables later
tcp: accecn: AccECN option failure handling
Ilpo Järvinen (13):
tcp: reorganize SYN ECN code
tcp: fast path functions later
tcp: AccECN core
tcp: accecn: AccECN negotiation
tcp: accecn: add AccECN rx byte counters
tcp: accecn: AccECN needs to know delivered bytes
tcp: sack option handling improvements
tcp: accecn: AccECN option
tcp: accecn: AccECN option send control
tcp: accecn: AccECN option ceb/cep heuristic
tcp: accecn: AccECN ACE field multi-wrap heuristic
tcp: accecn: try to fit AccECN option with SACK
tcp: try to avoid safer when ACKs are thinned
.../networking/net_cachelines/tcp_sock.rst | 14 +
include/linux/tcp.h | 34 +-
include/net/netns/ipv4.h | 2 +
include/net/tcp.h | 221 ++++++-
include/uapi/linux/tcp.h | 7 +
net/ipv4/syncookies.c | 3 +
net/ipv4/sysctl_net_ipv4.c | 19 +
net/ipv4/tcp.c | 30 +-
net/ipv4/tcp_input.c | 608 +++++++++++++++++-
net/ipv4/tcp_ipv4.c | 7 +-
net/ipv4/tcp_minisocks.c | 92 ++-
net/ipv4/tcp_output.c | 297 ++++++++-
net/ipv6/syncookies.c | 1 +
net/ipv6/tcp_ipv6.c | 1 +
14 files changed, 1237 insertions(+), 99 deletions(-)
--
2.34.1
Hello,
This patchset is our exploration of how to support 1G pages in guest_memfd, and
how the pages will be used in Confidential VMs.
The patchset covers:
+ How to get 1G pages
+ Allowing mmap() of guest_memfd to userspace so that both private and shared
memory can use the same physical pages
+ Splitting and reconstructing pages to support conversions and mmap()
+ How the VM, userspace and guest_memfd interact to support conversions
+ Selftests to test all the above
+ Selftests also demonstrate the conversion flow between VM, userspace and
guest_memfd.
Why 1G pages in guest memfd?
Bring guest_memfd to performance and memory savings parity with VMs that are
backed by HugeTLBfs.
+ Performance is improved with 1G pages by more TLB hits and faster page walks
on TLB misses.
+ Memory savings from 1G pages comes from HugeTLB Vmemmap Optimization (HVO).
Options for 1G page support:
1. HugeTLB
2. Contiguous Memory Allocator (CMA)
3. Other suggestions are welcome!
Comparison between options:
1. HugeTLB
+ Refactor HugeTLB to separate allocator from the rest of HugeTLB
+ Pro: Graceful transition for VMs backed with HugeTLB to guest_memfd
+ Near term: Allows co-tenancy of HugeTLB and guest_memfd backed VMs
+ Pro: Can provide iterative steps toward new future allocator
+ Unexplored: Managing userspace-visible changes
+ e.g. HugeTLB's free_hugepages will decrease if HugeTLB is used,
but not when future allocator is used
2. CMA
+ Port some HugeTLB features to be applied on CMA
+ Pro: Clean slate
What would refactoring HugeTLB involve?
(Some refactoring was done in this RFC, more can be done.)
1. Broadly involves separating the HugeTLB allocator from the rest of HugeTLB
+ Brings more modularity to HugeTLB
+ No functionality change intended
+ Likely step towards HugeTLB's integration into core-mm
2. guest_memfd will use just the allocator component of HugeTLB, not including
the complex parts of HugeTLB like
+ Userspace reservations (resv_map)
+ Shared PMD mappings
+ Special page walkers
What features would need to be ported to CMA?
+ Improved allocation guarantees
+ Per NUMA node pool of huge pages
+ Subpools per guest_memfd
+ Memory savings
+ Something like HugeTLB Vmemmap Optimization
+ Configuration/reporting features
+ Configuration of number of pages available (and per NUMA node) at and
after host boot
+ Reporting of memory usage/availability statistics at runtime
HugeTLB was picked as the source of 1G pages for this RFC because it allows a
graceful transition, and retains memory savings from HVO.
To illustrate this, if a host machine uses HugeTLBfs to back VMs, and a
confidential VM were to be scheduled on that host, some HugeTLBfs pages would
have to be given up and returned to CMA for guest_memfd pages to be rebuilt from
that memory. This requires memory to be reserved for HVO to be removed and
reapplied on the new guest_memfd memory. This not only slows down memory
allocation but also trims the benefits of HVO. Memory would have to be reserved
on the host to facilitate these transitions.
Improving how guest_memfd uses the allocator in a future revision of this RFC:
To provide an easier transition away from HugeTLB, guest_memfd's use of HugeTLB
should be limited to these allocator functions:
+ reserve(node, page_size, num_pages) => opaque handle
+ Used when a guest_memfd inode is created to reserve memory from backend
allocator
+ allocate(handle, mempolicy, page_size) => folio
+ To allocate a folio from guest_memfd's reservation
+ split(handle, folio, target_page_size) => void
+ To take a huge folio, and split it to smaller folios, restore to filemap
+ reconstruct(handle, first_folio, nr_pages) => void
+ To take a folio, and reconstruct a huge folio out of nr_pages from the
first_folio
+ free(handle, folio) => void
+ To return folio to guest_memfd's reservation
+ error(handle, folio) => void
+ To handle memory errors
+ unreserve(handle) => void
+ To return guest_memfd's reservation to allocator backend
Userspace should only provide a page size when creating a guest_memfd and should
not have to specify HugeTLB.
Overview of patches:
+ Patches 01-12
+ Many small changes to HugeTLB, mostly to separate HugeTLBfs concepts from
HugeTLB, and to expose HugeTLB functions.
+ Patches 13-16
+ Letting guest_memfd use HugeTLB
+ Creation of each guest_memfd reserves pages from HugeTLB's global hstate
and puts it into the guest_memfd inode's subpool
+ Each folio allocation takes a page from the guest_memfd inode's subpool
+ Patches 17-21
+ Selftests for new HugeTLB features in guest_memfd
+ Patches 22-24
+ More small changes on the HugeTLB side to expose functions needed by
guest_memfd
+ Patch 25:
+ Uses the newly available functions from patches 22-24 to split HugeTLB
pages. In this patch, HugeTLB folios are always split to 4K before any
usage, private or shared.
+ Patches 26-28
+ Allow mmap() in guest_memfd and faulting in shared pages
+ Patch 29
+ Enables conversion between private/shared pages
+ Patch 30
+ Required to zero folios after conversions to avoid leaking initialized
kernel memory
+ Patch 31-38
+ Add selftests to test mapping pages to userspace, guest/host memory
sharing and update conversions tests
+ Patch 33 illustrates the conversion flow between VM/userspace/guest_memfd
+ Patch 39
+ Dynamically split and reconstruct HugeTLB pages instead of always
splitting before use. All earlier selftests are expected to still pass.
TODOs:
+ Add logic to wait for safe_refcount [1]
+ Look into lazy splitting/reconstruction of pages
+ Currently, when the KVM_SET_MEMORY_ATTRIBUTES is invoked, not only is the
mem_attr_array and faultability updated, the pages in the requested range
are also split/reconstructed as necessary. We want to look into delaying
splitting/reconstruction to fault time.
+ Solve race between folios being faulted in and being truncated
+ When running private_mem_conversions_test with more than 1 vCPU, a folio
getting truncated may get faulted in by another process, causing elevated
mapcounts when the folio is freed (VM_BUG_ON_FOLIO).
+ Add intermediate splits (1G should first split to 2M and not split directly to
4K)
+ Use guest's lock instead of hugetlb_lock
+ Use multi-index xarray/replace xarray with some other data struct for
faultability flag
+ Refactor HugeTLB better, present generic allocator interface
Please let us know your thoughts on:
+ HugeTLB as the choice of transitional allocator backend
+ Refactoring HugeTLB to provide generic allocator interface
+ Shared/private conversion flow
+ Requiring user to request kernel to unmap pages from userspace using
madvise(MADV_DONTNEED)
+ Failing conversion on elevated mapcounts/pincounts/refcounts
+ Process of splitting/reconstructing page
+ Anything else!
[1] https://lore.kernel.org/all/20240829-guest-memfd-lib-v2-0-b9afc1ff3656@quic…
Ackerley Tng (37):
mm: hugetlb: Simplify logic in dequeue_hugetlb_folio_vma()
mm: hugetlb: Refactor vma_has_reserves() to should_use_hstate_resv()
mm: hugetlb: Remove unnecessary check for avoid_reserve
mm: mempolicy: Refactor out policy_node_nodemask()
mm: hugetlb: Refactor alloc_buddy_hugetlb_folio_with_mpol() to
interpret mempolicy instead of vma
mm: hugetlb: Refactor dequeue_hugetlb_folio_vma() to use mpol
mm: hugetlb: Refactor out hugetlb_alloc_folio
mm: truncate: Expose preparation steps for truncate_inode_pages_final
mm: hugetlb: Expose hugetlb_subpool_{get,put}_pages()
mm: hugetlb: Add option to create new subpool without using surplus
mm: hugetlb: Expose hugetlb_acct_memory()
mm: hugetlb: Move and expose hugetlb_zero_partial_page()
KVM: guest_memfd: Make guest mem use guest mem inodes instead of
anonymous inodes
KVM: guest_memfd: hugetlb: initialization and cleanup
KVM: guest_memfd: hugetlb: allocate and truncate from hugetlb
KVM: guest_memfd: Add page alignment check for hugetlb guest_memfd
KVM: selftests: Add basic selftests for hugetlb-backed guest_memfd
KVM: selftests: Support various types of backing sources for private
memory
KVM: selftests: Update test for various private memory backing source
types
KVM: selftests: Add private_mem_conversions_test.sh
KVM: selftests: Test that guest_memfd usage is reported via hugetlb
mm: hugetlb: Expose vmemmap optimization functions
mm: hugetlb: Expose HugeTLB functions for promoting/demoting pages
mm: hugetlb: Add functions to add/move/remove from hugetlb lists
KVM: guest_memfd: Track faultability within a struct kvm_gmem_private
KVM: guest_memfd: Allow mmapping guest_memfd files
KVM: guest_memfd: Use vm_type to determine default faultability
KVM: Handle conversions in the SET_MEMORY_ATTRIBUTES ioctl
KVM: guest_memfd: Handle folio preparation for guest_memfd mmap
KVM: selftests: Allow vm_set_memory_attributes to be used without
asserting return value of 0
KVM: selftests: Test using guest_memfd memory from userspace
KVM: selftests: Test guest_memfd memory sharing between guest and host
KVM: selftests: Add notes in private_mem_kvm_exits_test for mmap-able
guest_memfd
KVM: selftests: Test that pinned pages block KVM from setting memory
attributes to PRIVATE
KVM: selftests: Refactor vm_mem_add to be more flexible
KVM: selftests: Add helper to perform madvise by memslots
KVM: selftests: Update private_mem_conversions_test for mmap()able
guest_memfd
Vishal Annapurve (2):
KVM: guest_memfd: Split HugeTLB pages for guest_memfd use
KVM: guest_memfd: Dynamically split/reconstruct HugeTLB page
fs/hugetlbfs/inode.c | 35 +-
include/linux/hugetlb.h | 54 +-
include/linux/kvm_host.h | 1 +
include/linux/mempolicy.h | 2 +
include/linux/mm.h | 1 +
include/uapi/linux/kvm.h | 26 +
include/uapi/linux/magic.h | 1 +
mm/hugetlb.c | 346 ++--
mm/hugetlb_vmemmap.h | 11 -
mm/mempolicy.c | 36 +-
mm/truncate.c | 26 +-
tools/include/linux/kernel.h | 4 +-
tools/testing/selftests/kvm/Makefile | 3 +
.../kvm/guest_memfd_hugetlb_reporting_test.c | 222 +++
.../selftests/kvm/guest_memfd_pin_test.c | 104 ++
.../selftests/kvm/guest_memfd_sharing_test.c | 160 ++
.../testing/selftests/kvm/guest_memfd_test.c | 238 ++-
.../testing/selftests/kvm/include/kvm_util.h | 45 +-
.../testing/selftests/kvm/include/test_util.h | 18 +
tools/testing/selftests/kvm/lib/kvm_util.c | 443 +++--
tools/testing/selftests/kvm/lib/test_util.c | 99 ++
.../kvm/x86_64/private_mem_conversions_test.c | 158 +-
.../x86_64/private_mem_conversions_test.sh | 91 +
.../kvm/x86_64/private_mem_kvm_exits_test.c | 11 +-
virt/kvm/guest_memfd.c | 1563 ++++++++++++++++-
virt/kvm/kvm_main.c | 17 +
virt/kvm/kvm_mm.h | 16 +
27 files changed, 3288 insertions(+), 443 deletions(-)
create mode 100644 tools/testing/selftests/kvm/guest_memfd_hugetlb_reporting_test.c
create mode 100644 tools/testing/selftests/kvm/guest_memfd_pin_test.c
create mode 100644 tools/testing/selftests/kvm/guest_memfd_sharing_test.c
create mode 100755 tools/testing/selftests/kvm/x86_64/private_mem_conversions_test.sh
--
2.46.0.598.g6f2099f65c-goog