From: Sungho Bae <[email protected]>
The virtio-mmio legacy spec (Section 4.2.4) requires the driver to
write the guest page size "during initialization, before any queues
are used". Reset is step 1 of the initialization sequence
(Section 3.1), so setting GuestPageSize immediately after the status
register reset in vm_reset() is more proper.
Currently the GuestPageSize write lives in two separate call sites:
- virtio_mmio_probe(), before register_virtio_device()
- virtio_mmio_restore(), before virtio_device_restore()
Both of these write the value *before* the reset that happens inside
register_virtio_device()/virtio_device_restore(), so a device
implementation that clears GuestPageSize on reset would lose the
value. QEMU's virtio_mmio_reset() for example zeroes guest_page_shift
on a full device reset.
The current code happens to work because the Linux driver triggers
only a "soft reset" (STATUS register write of 0), and QEMU's
soft-reset path does not clear guest_page_shift. But relying on
this is fragile and not guaranteed by the spec.
Move the GuestPageSize write into vm_reset(), right after the status
reset. This ensures the value is set:
- at the correct point in the initialization sequence per spec,
- after every reset (probe, restore, or any future path), and
- exactly once, removing the duplication.
Fixes: e0c2ce821795 ("virtio_mmio: Restore guest page size on resume")
Signed-off-by: Sungho Bae <[email protected]>
---
drivers/virtio/virtio_mmio.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index 595c2274fbb5..daa65b269a36 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -254,6 +254,16 @@ static void vm_reset(struct virtio_device *vdev)
/* 0 status means a reset. */
writel(0, vm_dev->base + VIRTIO_MMIO_STATUS);
+
+ /*
+ * The virtio-mmio legacy spec requires the driver to write the
+ * guest page size during initialization, before any queues are
+ * used. Since reset is step 1 of initialization (Section 3.1),
+ * set it here so it is always in place for subsequent queue setup
+ * in every code path (probe, restore, etc.).
+ */
+ if (vm_dev->version == 1)
+ writel(PAGE_SIZE, vm_dev->base + VIRTIO_MMIO_GUEST_PAGE_SIZE);
}
@@ -547,9 +557,6 @@ static int virtio_mmio_restore(struct device *dev)
{
struct virtio_mmio_device *vm_dev = dev_get_drvdata(dev);
- if (vm_dev->version == 1)
- writel(PAGE_SIZE, vm_dev->base + VIRTIO_MMIO_GUEST_PAGE_SIZE);
-
return virtio_device_restore(&vm_dev->vdev);
}
@@ -619,8 +626,6 @@ static int virtio_mmio_probe(struct platform_device *pdev)
vm_dev->vdev.id.vendor = readl(vm_dev->base + VIRTIO_MMIO_VENDOR_ID);
if (vm_dev->version == 1) {
- writel(PAGE_SIZE, vm_dev->base + VIRTIO_MMIO_GUEST_PAGE_SIZE);
-
rc = dma_set_mask(&pdev->dev, DMA_BIT_MASK(64));
/*
* In the legacy case, ensure our coherently-allocated virtio
--
2.43.0
