[PULL 2/9] s390x/pci: fix interrupt blocking by returning only the device's summary bit

[Thomas Huth <thuth@redhat.com>]

From: Jaehoon Kim <jhkim@linux.ibm.com>

Previously, set_ind_atomic() returned the entire byte containing
multiple summary bits. This meant that if any other summary bit in the
byte was set, interrupt injection could be incorrectly blocked, even
when the current device's summary bit was not set. As a result, the
guest could remain blocked after I/O completion during FIO tests.

This patch replaces set_ind_atomic() with set_ind_bit_atomic(), which
returns true if the bit was set by this function, and false if it was
already set or mapping failed. Interrupts are now blocked only when
the device's own summary bit was not previously set, avoiding
unintended blocking when multiple PCI summary bits exist within the
same byte.

Signed-off-by: Jaehoon Kim <jhkim@linux.ibm.com>
Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Message-ID: <20251001154004.71917-1-jhkim@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 hw/s390x/s390-pci-bus.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
index f87d2748b63..e8e41c8a9a1 100644
--- a/hw/s390x/s390-pci-bus.c
+++ b/hw/s390x/s390-pci-bus.c
@@ -652,7 +652,16 @@ static const PCIIOMMUOps s390_iommu_ops = {
     .get_address_space = s390_pci_dma_iommu,
 };
 
-static uint8_t set_ind_atomic(uint64_t ind_loc, uint8_t to_be_set)
+/**
+ * set_ind_bit_atomic - Atomically set a bit in an indicator
+ *
+ * @ind_loc:   Address of the indicator
+ * @to_be_set: Bit to set
+ *
+ * Returns true if the bit was set by this function, false if it was
+ * already set or mapping failed.
+ */
+static bool set_ind_bit_atomic(uint64_t ind_loc, uint8_t to_be_set)
 {
     uint8_t expected, actual;
     hwaddr len = 1;
@@ -662,7 +671,7 @@ static uint8_t set_ind_atomic(uint64_t ind_loc, uint8_t to_be_set)
     ind_addr = cpu_physical_memory_map(ind_loc, &len, true);
     if (!ind_addr) {
         s390_pci_generate_error_event(ERR_EVENT_AIRERR, 0, 0, 0, 0);
-        return -1;
+        return false;
     }
     actual = *ind_addr;
     do {
@@ -671,7 +680,7 @@ static uint8_t set_ind_atomic(uint64_t ind_loc, uint8_t to_be_set)
     } while (actual != expected);
     cpu_physical_memory_unmap((void *)ind_addr, len, 1, len);
 
-    return actual;
+    return (actual & to_be_set) ? false : true;
 }
 
 static void s390_msi_ctrl_write(void *opaque, hwaddr addr, uint64_t data,
@@ -693,10 +702,10 @@ static void s390_msi_ctrl_write(void *opaque, hwaddr addr, uint64_t data,
     ind_bit = pbdev->routes.adapter.ind_offset;
     sum_bit = pbdev->routes.adapter.summary_offset;
 
-    set_ind_atomic(pbdev->routes.adapter.ind_addr + (ind_bit + vec) / 8,
+    set_ind_bit_atomic(pbdev->routes.adapter.ind_addr + (ind_bit + vec) / 8,
                    0x80 >> ((ind_bit + vec) % 8));
-    if (!set_ind_atomic(pbdev->routes.adapter.summary_addr + sum_bit / 8,
-                                       0x80 >> (sum_bit % 8))) {
+    if (set_ind_bit_atomic(pbdev->routes.adapter.summary_addr + sum_bit / 8,
+                   0x80 >> (sum_bit % 8))) {
         css_adapter_interrupt(CSS_IO_ADAPTER_PCI, pbdev->isc);
     }
 }
-- 
2.51.0