Commit 44247094 authored Mar 28, 2023 by Saurabh Sengar Committed by Greg Kroah-Hartman May 17, 2023

x86/ioapic: Don't return 0 from arch_dynirq_lower_bound()

[ Upstream commit 5af507bef93c09a94fb8f058213b489178f4cbe5 ]

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: 3e5bedc2 ("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>

parent 824683db

arch/x86/kernel/apic/io_apic.c

+9 −5

Original line number	Diff line number	Diff line
		@@ -2455,17 +2455,21 @@ static int io_apic_get_redir_entries(int ioapic)

		unsigned int arch_dynirq_lower_bound(unsigned int from)
		{
		unsigned int ret;

		/*
		* dmar_alloc_hwirq() may be called before setup_IO_APIC(), so use
		* gsi_top if ioapic_dynirq_base hasn't been initialized yet.
		*/
		if (!ioapic_initialized)
		return gsi_top;
		ret = ioapic_dynirq_base ? : gsi_top;

		/*
		* For DT enabled machines ioapic_dynirq_base is irrelevant and not
		* updated. So simply return @from if ioapic_dynirq_base == 0.
		* For DT enabled machines ioapic_dynirq_base is irrelevant and
		* always 0. gsi_top can be 0 if there is no IO/APIC registered.
		* 0 is an invalid interrupt number for dynamic allocations. Return
		* @from instead.
		*/
		return ioapic_dynirq_base ? : from;
		return ret ? : from;
		}

		#ifdef CONFIG_X86_32