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

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Date:   Mon, 21 Sep 2020 12:51:16 +0800
From:   Zenghui Yu <yuzenghui@...wei.com>
To:     <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     <alex.williamson@...hat.com>, <cohuck@...hat.com>,
        <wanghaibin.wang@...wei.com>, Zenghui Yu <yuzenghui@...wei.com>
Subject: [PATCH v2 2/2] vfio/pci: Don't regenerate vconfig for all BARs if !bardirty

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@...hat.com>
Signed-off-by: Zenghui Yu <yuzenghui@...wei.com>
---
* 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++) {
-- 
2.19.1