powerpc/xive: Use XIVE_BAD_IRQ instead of zero to catch non configured IPIs

When a CPU is brought up, an IPI number is allocated and recorded
under the XIVE CPU structure. Invalid IPI numbers are tracked with
interrupt number 0x0.

On the PowerNV platform, the interrupt number space starts at 0x10 and
this works fine. However, on the sPAPR platform, it is possible to
allocate the interrupt number 0x0 and this raises an issue when CPU 0
is unplugged. The XIVE spapr driver tracks allocated interrupt numbers
in a bitmask and it is not correctly updated when interrupt number 0x0
is freed. It stays allocated and it is then impossible to reallocate.

Fix by using the XIVE_BAD_IRQ value instead of zero on both platforms.

Reported-by: David Gibson <[email protected]>
Fixes: eac1e731b59e ("powerpc/xive: guest exploitation of the XIVE interrupt controller")
Cc: [email protected] # v4.14+
Signed-off-by: Cédric Le Goater <[email protected]>
Reviewed-by: David Gibson <[email protected]>
Tested-by: David Gibson <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

1 files changed, 2 insertions, 2 deletions

diff --git a/arch/powerpc/sysdev/xive/native.c b/arch/powerpc/sysdev/xive/native.c
index 0ff6b739052c..50e1a8e02497 100644
--- a/arch/powerpc/sysdev/xive/native.c
+++ b/arch/powerpc/sysdev/xive/native.c
@@ -312,7 +312,7 @@ static void xive_native_put_ipi(unsigned int cpu, struct xive_cpu *xc)
 	s64 rc;
 
 	/* Free the IPI */
-	if (!xc->hw_ipi)
+	if (xc->hw_ipi == XIVE_BAD_IRQ)
 		return;
 	for (;;) {
 		rc = opal_xive_free_irq(xc->hw_ipi);
@@ -320,7 +320,7 @@ static void xive_native_put_ipi(unsigned int cpu, struct xive_cpu *xc)
 			msleep(OPAL_BUSY_DELAY_MS);
 			continue;
 		}
-		xc->hw_ipi = 0;
+		xc->hw_ipi = XIVE_BAD_IRQ;
 		break;
 	}
 }