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Saurabh Sengar 3df8a87394 x86/ioapic: Don't return 0 from arch_dynirq_lower_bound() 
[ Upstream commit 5af507bef9 ]

arch_dynirq_lower_bound() is invoked by the core interrupt code to
retrieve the lowest possible Linux interrupt number for dynamically
allocated interrupts like MSI.

The x86 implementation uses this to exclude the IO/APIC GSI space.
This works correctly as long as there is an IO/APIC registered, but
returns 0 if not. This has been observed in VMs where the BIOS does
not advertise an IO/APIC.

0 is an invalid interrupt number except for the legacy timer interrupt
on x86. The return value is unchecked in the core code, so it ends up
to allocate interrupt number 0 which is subsequently considered to be
invalid by the caller, e.g. the MSI allocation code.

The function has already a check for 0 in the case that an IO/APIC is
registered, as ioapic_dynirq_base is 0 in case of device tree setups.

Consolidate this and zero check for both ioapic_dynirq_base and gsi_top,
which is used in the case that no IO/APIC is registered.

Fixes: 3e5bedc2c2 ("x86/apic: Fix arch_dynirq_lower_bound() bug for DT enabled machines")
Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/1679988604-20308-1-git-send-email-ssengar@linux.microsoft.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2023-05-11 23:03:16 +09:00
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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 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.