diff mbox series

[1/2] x86/irq: fix calculation of max PV dom0 pIRQs

Message ID 20241120113555.38146-2-roger.pau@citrix.com (mailing list archive)
State New
Headers show
Series x86/irq: fix calculation of maximum pIRQs for dom0 | expand

Commit Message

Roger Pau Monne Nov. 20, 2024, 11:35 a.m. UTC 
The current calculation of PV dom0 pIRQs uses:

n = min(fls(num_present_cpus()), dom0_max_vcpus());

The usage of fls() is wrong, as num_present_cpus() already returns the number
of present CPUs, not the bitmap mask of CPUs.

Fix by removing the usage of fls().

Fixes: 7e73a6e7f12a ('have architectures specify the number of PIRQs a hardware domain gets')
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
 xen/arch/x86/io_apic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Andrew Cooper Nov. 20, 2024, 12:06 p.m. UTC | #1 
On 20/11/2024 11:35 am, Roger Pau Monne wrote:
> The current calculation of PV dom0 pIRQs uses:
>
> n = min(fls(num_present_cpus()), dom0_max_vcpus());
>
> The usage of fls() is wrong, as num_present_cpus() already returns the number
> of present CPUs, not the bitmap mask of CPUs.
>
> Fix by removing the usage of fls().
>
> Fixes: 7e73a6e7f12a ('have architectures specify the number of PIRQs a hardware domain gets')
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>

Yeah, that fls() fails the dimensional analysis sniff test.

Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

Is there any hint as to what the reasoning was?

~Andrew
diff mbox series

Patch

diff --git a/xen/arch/x86/io_apic.c b/xen/arch/x86/io_apic.c
index d44d2c9a4173..bd5ad61c85e4 100644
--- a/xen/arch/x86/io_apic.c
+++ b/xen/arch/x86/io_apic.c
@@ -2744,7 +2744,7 @@  void __init ioapic_init(void)
 
 unsigned int __hwdom_init arch_hwdom_irqs(const struct domain *d)
 {
-    unsigned int n = fls(num_present_cpus());
+    unsigned int n = num_present_cpus();
     /* Bounding by the domain pirq EOI bitmap capacity. */
     const unsigned int max_irqs = min_t(unsigned int, nr_irqs,
                                         PAGE_SIZE * BITS_PER_BYTE);