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Timothy Pearson 47ed17f2cb 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 15:34:30 -05:00
arch sparc64: fix prototypes of reads[bwl]() 2025-11-13 15:34:28 -05:00
block blk-cgroup: fix possible deadlock while configuring policy 2025-11-13 15:34:07 -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 16:33:42 +02:00
Documentation dpll: spec: add missing module-name and clock-id to pin-get reply 2025-11-13 15:33:59 -05:00
drivers vfio/pci: Fix INTx handling on legacy non-PCI 2.3 devices 2025-11-13 15:34:30 -05:00
fs ext4: increase IO priority of fastcommit 2025-11-13 15:34:30 -05:00
include scsi: ufs: core: Disable timestamp functionality if not supported 2025-11-13 15:34:25 -05:00
init init: handle bootloader identifier in kernel parameters 2025-10-19 16:33:50 +02:00
io_uring io_uring/zctx: check chained notif contexts 2025-11-13 15:34:03 -05:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:11:22 +01:00
kernel uprobe: Do not emulate/sstep original instruction when ip is changed 2025-11-13 15:34:07 -05:00
lib kunit: test_dev_action: Correctly cast 'priv' pointer to long* 2025-11-13 15:33:57 -05:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm: prevent poison consumption when splitting THP 2025-10-29 14:08:57 +01:00
net net: bridge: Install FDB for bridge MAC on VLAN 0 2025-11-13 15:34:29 -05:00
rust mm/ksm: fix flag-dropping behavior in ksm_madvise 2025-10-23 16:20:47 +02:00
samples ftrace/samples: Fix function size computation 2025-09-19 16:35:44 +02:00
scripts gcc-plugins: Remove TODO_verify_il for GCC >= 16 2025-10-06 11:17:52 +02:00
security KEYS: trusted_tpm1: Compare HMAC values in constant time 2025-10-19 16:33:51 +02:00
sound ASoC: tlv320aic3x: Fix class-D initialization for tlv320aic3007 2025-11-13 15:34:30 -05:00
tools selftests: forwarding: Reorder (ar)ping arguments to obey POSIX getopt 2025-11-13 15:34:28 -05:00
usr kbuild: hdrcheck: fix cross build with clang 2025-03-13 13:02:18 +01:00
virt KVM: Allow CPU to reschedule while setting per-page memory attributes 2025-07-17 18:37:08 +02:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml rust: give Clippy the minimum supported Rust version 2025-08-01 09:48:44 +01:00
.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 Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: introduce .clippy.toml 2025-03-13 13:01:42 +01:00
.mailmap mailmap: add entry for Thorsten Blum 2024-11-07 14:14:59 -08:00
.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: Remove self from DSA entry 2024-11-03 12:52:38 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: Update Alexey Makhalov's email address 2025-05-22 14:29:46 +02:00
Makefile Linux 6.12.57 2025-11-02 22:15:23 +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.