It was found that in a crash scenario, the remoteIRR bit in an IO-APIC
RTE could be left set, causing problems when bringing up a kdump
kernel. While this generally is most important to be taken care of in
the new kernel (which usually would be a native one), it still seems
desirable to also address this problem in Xen so that (a) the problem
doesn't bite Xen when used as a secondary emergency kernel and (b) an
attempt is being made to save un-fixed secondary kernels from running
into said problem.
Based on a Linux patch from suresh.b.siddha@xxxxxxxxxx
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
--- a/xen/arch/x86/io_apic.c
+++ b/xen/arch/x86/io_apic.c
@@ -382,11 +382,46 @@ static void clear_IO_APIC_pin(unsigned i
return;
/*
+ * Make sure the entry is masked and re-read the contents to check
+ * if it is a level triggered pin and if the remoteIRR is set.
+ */
+ if (!entry.mask) {
+ entry.mask = 1;
+ __ioapic_write_entry(apic, pin, FALSE, entry);
+ }
+ entry = __ioapic_read_entry(apic, pin, TRUE);
+
+ if (entry.irr) {
+ /* Make sure the trigger mode is set to level. */
+ if (!entry.trigger) {
+ entry.trigger = 1;
+ __ioapic_write_entry(apic, pin, TRUE, entry);
+ }
+ if (mp_ioapics[apic].mpc_apicver >= 0x20)
+ io_apic_eoi(apic, entry.vector);
+ else {
+ /*
+ * Mechanism by which we clear remoteIRR in this case is by
+ * changing the trigger mode to edge and back to level.
+ */
+ entry.trigger = 0;
+ __ioapic_write_entry(apic, pin, TRUE, entry);
+ entry.trigger = 1;
+ __ioapic_write_entry(apic, pin, TRUE, entry);
+ }
+ }
+
+ /*
* Disable it in the IO-APIC irq-routing table:
*/
memset(&entry, 0, sizeof(entry));
entry.mask = 1;
__ioapic_write_entry(apic, pin, TRUE, entry);
+
+ entry = __ioapic_read_entry(apic, pin, TRUE);
+ if (entry.irr)
+ printk(KERN_ERR "IO-APIC%02x-%u: Unable to reset IRR\n",
+ IO_APIC_ID(apic), pin);
}
static void clear_IO_APIC (void)
x86-ioapic-clear-irr.patch
Description: Text document
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