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7d5ec3d361
When MSI-X is enabled the ordering of calls is:
msix_map_region();
msix_setup_entries();
pci_msi_setup_msi_irqs();
msix_program_entries();
This has a few interesting issues:
1) msix_setup_entries() allocates the MSI descriptors and initializes them
except for the msi_desc:masked member which is left zero initialized.
2) pci_msi_setup_msi_irqs() allocates the interrupt descriptors and sets
up the MSI interrupts which ends up in pci_write_msi_msg() unless the
interrupt chip provides its own irq_write_msi_msg() function.
3) msix_program_entries() does not do what the name suggests. It solely
updates the entries array (if not NULL) and initializes the masked
member for each MSI descriptor by reading the hardware state and then
masks the entry.
Obviously this has some issues:
1) The uninitialized masked member of msi_desc prevents the enforcement
of masking the entry in pci_write_msi_msg() depending on the cached
masked bit. Aside of that half initialized data is a NONO in general
2) msix_program_entries() only ensures that the actually allocated entries
are masked. This is wrong as experimentation with crash testing and
crash kernel kexec has shown.
This limited testing unearthed that when the production kernel had more
entries in use and unmasked when it crashed and the crash kernel
allocated a smaller amount of entries, then a full scan of all entries
found unmasked entries which were in use in the production kernel.
This is obviously a device or emulation issue as the device reset
should mask all MSI-X table entries, but obviously that's just part
of the paper specification.
Cure this by:
1) Masking all table entries in hardware
2) Initializing msi_desc::masked in msix_setup_entries()
3) Removing the mask dance in msix_program_entries()
4) Renaming msix_program_entries() to msix_update_entries() to
reflect the purpose of that function.
As the masking of unused entries has never been done the Fixes tag refers
to a commit in:
git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
Fixes: f036d4ea5fa7 ("[PATCH] ia32 Message Signalled Interrupt support")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210729222542.403833459@linutronix.de
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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 Restructured Text 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.