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Timothy Pearson 8a8c9bfc45 vfio/pci: Fix INTx handling on legacy non-PCI 2.3 devices 
[ Upstream commit 8b9f128947 ]

PCI devices prior to PCI 2.3 both use level interrupts and do not support
interrupt masking, leading to a failure when passed through to a KVM guest on
at least the ppc64 platform. This failure manifests as receiving and
acknowledging a single interrupt in the guest, while the device continues to
assert the level interrupt indicating a need for further servicing.

When lazy IRQ masking is used on DisINTx- (non-PCI 2.3) hardware, the following
sequence occurs:

 * Level IRQ assertion on device
 * IRQ marked disabled in kernel
 * Host interrupt handler exits without clearing the interrupt on the device
 * Eventfd is delivered to userspace
 * Guest processes IRQ and clears device interrupt
 * Device de-asserts INTx, then re-asserts INTx while the interrupt is masked
 * Newly asserted interrupt acknowledged by kernel VMM without being handled
 * Software mask removed by VFIO driver
 * Device INTx still asserted, host controller does not see new edge after EOI

The behavior is now platform-dependent.  Some platforms (amd64) will continue
to spew IRQs for as long as the INTX line remains asserted, therefore the IRQ
will be handled by the host as soon as the mask is dropped.  Others (ppc64) will
only send the one request, and if it is not handled no further interrupts will
be sent.  The former behavior theoretically leaves the system vulnerable to
interrupt storm, and the latter will result in the device stalling after
receiving exactly one interrupt in the guest.

Work around this by disabling lazy IRQ masking for DisINTx- INTx devices.

Signed-off-by: Timothy Pearson <tpearson@raptorengineering.com>
Link: https://lore.kernel.org/r/333803015.1744464.1758647073336.JavaMail.zimbra@raptorengineeringinc.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-11-13 15:37:32 -05:00
arch sparc64: fix prototypes of reads[bwl]() 2025-11-13 15:37:28 -05:00
block blk-cgroup: fix possible deadlock while configuring policy 2025-11-13 15:36:52 -05:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: essiv - Check ssize for decryption and in-place encryption 2025-10-19 16:37:14 +02:00
Documentation dt-bindings: display/msm/gmu: Update Adreno 623 bindings 2025-11-13 15:37:16 -05:00
drivers vfio/pci: Fix INTx handling on legacy non-PCI 2.3 devices 2025-11-13 15:37:32 -05:00
fs ext4: increase IO priority of fastcommit 2025-11-13 15:37:31 -05:00
include scsi: ufs: core: Change MCQ interrupt enable flow 2025-11-13 15:37:30 -05:00
init init: handle bootloader identifier in kernel parameters 2025-10-19 16:37:27 +02:00
io_uring io_uring/zcrx: account niov arrays to cgroup 2025-11-13 15:36:51 -05:00
ipc vfs-6.17-rc1.mmap_prepare 2025-07-28 13:43:25 -07:00
kernel uprobe: Do not emulate/sstep original instruction when ip is changed 2025-11-13 15:36:53 -05:00
lib kunit: Enable PCI on UML without triggering WARN() 2025-11-13 15:36:51 -05:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm treewide: remove MIGRATEPAGE_SUCCESS 2025-10-29 14:10:32 +01:00
net net: bridge: Install FDB for bridge MAC on VLAN 0 2025-11-13 15:37:30 -05:00
rust rust: kunit: allow cfg on tests 2025-11-13 15:36:51 -05:00
samples 15 hotfixes. 11 are cc:stable and the remainder address post-6.16 issues 2025-09-17 21:34:26 -07:00
scripts docs: kernel-doc: avoid script crash on ancient Python 2025-11-13 15:36:58 -05:00
security KEYS: trusted_tpm1: Compare HMAC values in constant time 2025-10-19 16:37:28 +02:00
sound ASoC: tlv320aic3x: Fix class-D initialization for tlv320aic3007 2025-11-13 15:37:32 -05:00
tools selftests: forwarding: Reorder (ar)ping arguments to obey POSIX getopt 2025-11-13 15:37:29 -05:00
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 6.17.7 2025-11-02 22:18:05 +09:00
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.