[Qemu-devel] [PATCH 2/2] vfio: Do not reattempt a failed rom read

[Bandan Das]

During lazy rom loading, if rom read fails, and the
guest attempts a read again, vfio_rom_read will again attempt it.
Add a boolean to prevent this. There could be a case where
a failed rom read might succeed the next time because of
a device reset or such, but it's best to exclude unpredictable
behavior

Signed-off-by: Bandan Das <b...@redhat.com>
---
 hw/misc/vfio.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/hw/misc/vfio.c b/hw/misc/vfio.c
index e5b2826..c500067 100644
--- a/hw/misc/vfio.c
+++ b/hw/misc/vfio.c
@@ -191,6 +191,7 @@ typedef struct VFIODevice {
     bool has_flr;
     bool has_pm_reset;
     bool needs_reset;
+    bool rom_read_failed;
 } VFIODevice;
 
 typedef struct VFIOGroup {
@@ -1125,6 +1126,7 @@ static void vfio_pci_load_rom(VFIODevice *vdev)
     vdev->rom_offset = reg_info.offset;
 
     if (!vdev->rom_size) {
+        vdev->rom_read_failed = true;
         error_report_once("vfio-pci: Cannot read device rom at "
                     "%04x:%02x:%02x.%x\n",
                     vdev->host.domain, vdev->host.bus, vdev->host.slot,
@@ -1161,7 +1163,7 @@ static uint64_t vfio_rom_read(void *opaque, hwaddr addr, 
unsigned size)
     uint64_t val = ((uint64_t)1 << (size * 8)) - 1;
 
     /* Load the ROM lazily when the guest tries to read it */
-    if (unlikely(!vdev->rom)) {
+    if (unlikely(!vdev->rom_read_failed && !vdev->rom)) {
         vfio_pci_load_rom(vdev);
     }
 
@@ -1230,6 +1232,7 @@ static void vfio_pci_size_rom(VFIODevice *vdev)
                      PCI_BASE_ADDRESS_SPACE_MEMORY, &vdev->pdev.rom);
 
     vdev->pdev.has_rom = true;
+    vdev->rom_read_failed = false;
 }
 
 static void vfio_vga_write(void *opaque, hwaddr addr,
-- 
1.8.3.1