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Naman Jain e29587c075 uio_hv_generic: Let userspace take care of interrupt mask 
commit b15b7d2a1b upstream.

Remove the logic to set interrupt mask by default in uio_hv_generic
driver as the interrupt mask value is supposed to be controlled
completely by the user space. If the mask bit gets changed
by the driver, concurrently with user mode operating on the ring,
the mask bit may be set when it is supposed to be clear, and the
user-mode driver will miss an interrupt which will cause a hang.

For eg- when the driver sets inbound ring buffer interrupt mask to 1,
the host does not interrupt the guest on the UIO VMBus channel.
However, setting the mask does not prevent the host from putting a
message in the inbound ring buffer. So let’s assume that happens,
the host puts a message into the ring buffer but does not interrupt.

Subsequently, the user space code in the guest sets the inbound ring
buffer interrupt mask to 0, saying “Hey, I’m ready for interrupts”.
User space code then calls pread() to wait for an interrupt.
Then one of two things happens:

* The host never sends another message. So the pread() waits forever.
* The host does send another message. But because there’s already a
  message in the ring buffer, it doesn’t generate an interrupt.
  This is the correct behavior, because the host should only send an
  interrupt when the inbound ring buffer transitions from empty to
  not-empty. Adding an additional message to a ring buffer that is not
  empty is not supposed to generate an interrupt on the guest.
  Since the guest is waiting in pread() and not removing messages from
  the ring buffer, the pread() waits forever.

This could be easily reproduced in hv_fcopy_uio_daemon if we delay
setting interrupt mask to 0.

Similarly if hv_uio_channel_cb() sets the interrupt_mask to 1,
there’s a race condition. Once user space empties the inbound ring
buffer, but before user space sets interrupt_mask to 0, the host could
put another message in the ring buffer but it wouldn’t interrupt.
Then the next pread() would hang.

Fix these by removing all instances where interrupt_mask is changed,
while keeping the one in set_event() unchanged to enable userspace
control the interrupt mask by writing 0/1 to /dev/uioX.

Fixes: 95096f2fbd ("uio-hv-generic: new userspace i/o driver for VMBus")
Suggested-by: John Starks <jostarks@microsoft.com>
Signed-off-by: Naman Jain <namjain@linux.microsoft.com>
Cc: stable@vger.kernel.org
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Long Li <longli@microsoft.com>
Reviewed-by: Tianyu Lan <tiala@microsoft.com>
Tested-by: Tianyu Lan <tiala@microsoft.com>
Link: https://lore.kernel.org/r/20250828044200.492030-1-namjain@linux.microsoft.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-10-15 12:04:15 +02:00
arch sparc: fix accurate exception reporting in copy_{from,to}_user for M7 2025-10-15 12:04:03 +02:00
block blk-throttle: fix throtl_data leak during disk release 2025-10-15 12:03:34 +02:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto KEYS: X.509: Fix Basic Constraints CA flag parsing 2025-10-15 12:04:11 +02:00
Documentation Documentation: trace: historgram-design: Separate sched_waking histogram section heading and the following diagram 2025-10-15 12:04:01 +02:00
drivers uio_hv_generic: Let userspace take care of interrupt mask 2025-10-15 12:04:15 +02:00
fs Squashfs: fix uninit-value in squashfs_get_parent 2025-10-15 12:04:15 +02:00
include nfs/localio: avoid issuing misaligned IO using O_DIRECT 2025-10-15 12:04:13 +02:00
init Fix CC_HAS_ASM_GOTO_OUTPUT on non-x86 architectures 2025-10-15 12:03:13 +02:00
io_uring io_uring-6.17-20250919 2025-09-19 12:10:49 -07:00
ipc vfs-6.17-rc1.mmap_prepare 2025-07-28 13:43:25 -07:00
kernel bpf: Reject negative offsets for ALU ops 2025-10-15 12:04:14 +02:00
lib vdso/datastore: Gate time data behind CONFIG_GENERIC_GETTIMEOFDAY 2025-10-15 12:03:24 +02:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm mm/slub: Fix cmp_loc_by_count() to return 0 when counts are equal 2025-10-15 12:03:56 +02:00
net tcp: use skb->len instead of skb->truesize in tcp_can_ingest() 2025-10-15 12:04:12 +02:00
rust rust: cpumask: Mark CpumaskVar as transparent 2025-10-15 12:03:19 +02:00
samples 15 hotfixes. 11 are cc:stable and the remainder address post-6.16 issues 2025-09-17 21:34:26 -07:00
scripts scripts/misc-check: update export checks for EXPORT_SYMBOL_FOR_MODULES() 2025-10-15 12:03:22 +02:00
security lsm: CONFIG_LSM can depend on CONFIG_SECURITY 2025-10-15 12:03:17 +02:00
sound ALSA: hda/realtek: Add quirk for HP Spectre 14t-ea100 2025-10-15 12:04:15 +02:00
tools selftests/bpf: Fix realloc size in bpf_get_addrs 2025-10-15 12:04:14 +02:00
usr usr/include: openrisc: don't HDRTEST bpf_perf_event.h 2025-05-12 15:03:17 +09:00
virt Merge tag 'kvm-x86-no_assignment-6.17' of https://github.com/kvm-x86/linux into HEAD 2025-07-29 08:36:42 -04:00
.clang-format Linux 6.15-rc5 2025-05-06 16:39:25 +10:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore gitignore: allow .pylintrc to be tracked 2025-07-02 17:10:04 -06:00
.mailmap 7 hotfixes. 4 are cc:stable and the remainder address post-6.16 issues or 2025-09-28 09:32:00 -07:00
.pylintrc docs: add a .pylintrc file with sys path for docs scripts 2025-04-09 12:10:33 -06:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: retire Boris from TLS maintainers 2025-08-26 17:36:01 -07:00
Kbuild drm: ensure drm headers are self-contained and pass kernel-doc 2025-02-12 10:44:43 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS i2c-for-6.17-rc8 2025-09-28 13:19:23 -07:00
Makefile Linux 6.17.2 2025-10-12 13:01:58 +02:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.