[PATCH v2 2/2] vfio/pci: Don't regenerate vconfig for all BARs if !bardirty

From: Zenghui Yu
Date: Mon Sep 21 2020 - 00:51:45 EST

Now we regenerate vconfig for all the BARs via vfio_bar_fixup(), every time
any offset of any of them are read. Though BARs aren't re-read regularly,
the regeneration can be avoid if no BARs had been written since they were
last read, in which case the vdev->bardirty is false.

Let's predicate the vfio_bar_fixup() on the bardirty so that it can return
immediately if !bardirty.

Suggested-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
Signed-off-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
* From v1:
- Per Alex's suggestion, let vfio_bar_fixup() test vdev->bardirty to
avoid doing work if bardirty is false, instead of removing it entirely.
- Rewrite the commit message.

drivers/vfio/pci/vfio_pci_config.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
index d98843feddce..5e02ba07e8e8 100644
--- a/drivers/vfio/pci/vfio_pci_config.c
+++ b/drivers/vfio/pci/vfio_pci_config.c
@@ -467,6 +467,9 @@ static void vfio_bar_fixup(struct vfio_pci_device *vdev)
__le32 *vbar;
u64 mask;

+ if (!vdev->bardirty)
+ return;
vbar = (__le32 *)&vdev->vconfig[PCI_BASE_ADDRESS_0];

for (i = 0; i < PCI_STD_NUM_BARS; i++, vbar++) {