Messages in this thread | | | Date | Tue, 28 Mar 2023 06:59:04 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH v2] x86/ioapic: Don't ret urn 0 from arch dynirq lower bound() |
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On March 28, 2023 12:30:04 AM PDT, Saurabh Sengar <ssengar@linux.microsoft.com> wrote: >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, but 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: 3e5bedc2c258 ("x86/apic: Fix arch_dynirq_lower_bound() bug for DT enabled machines") >Co-developed-by: Thomas Gleixner <tglx@linutronix.de> >Signed-off-by: Thomas Gleixner <tglx@linutronix.de> >Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com> >Cc: Andy Shevchenko <andriy.shevchenko@intel.com> >Cc: Thomas Gleixner <tglx@linutronix.de> >--- >[V2] >- Edit commit message >- Consolidated the 0 check for ioapic_dynirq_base as well > > arch/x86/kernel/apic/io_apic.c | 14 +++++++++----- > 1 file changed, 9 insertions(+), 5 deletions(-) > >diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c >index 1f83b052bb74..f980b38b0227 100644 >--- a/arch/x86/kernel/apic/io_apic.c >+++ b/arch/x86/kernel/apic/io_apic.c >@@ -2477,17 +2477,21 @@ 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
Is there any reason why this variable can't be initialized to a fixed nonzero number, like 16?
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