Since Linux commit 7d5ec3d36123 ("PCI/MSI: Mask all unused MSI-X
entries"), kvmtool segfaults when the guest boots and tries to
disable all the MSI-X entries of a virtio device while MSI-X itself
is disabled.
What Linux does is seems perfectly correct. However, kvmtool uses
a different decoding depending on whether MSI-X is enabled for
this device or not. Which seems pretty wrong.
Cure the problem by removing the check against MSI-X being enabled,
and simplify the whole logic which looked a bit odd. With this,
Linux is back booting as a kvmtool guest with MSI-X.
Cc: Andre Przywara <Andre.Przywara@xxxxxxx>
Cc: Alexandru Elisei <alexandru.elisei@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
---
include/kvm/virtio.h | 2 +-
virtio/core.c | 12 ++++--------
virtio/pci.c | 7 ++-----
3 files changed, 7 insertions(+), 14 deletions(-)
diff --git a/include/kvm/virtio.h b/include/kvm/virtio.h
index 3a311f54..7047d36f 100644
--- a/include/kvm/virtio.h
+++ b/include/kvm/virtio.h
@@ -166,7 +166,7 @@ u16 virt_queue__get_head_iov(struct virt_queue *vq, struct iovec iov[],
u16 virt_queue__get_inout_iov(struct kvm *kvm, struct virt_queue *queue,
struct iovec in_iov[], struct iovec out_iov[],
u16 *in, u16 *out);
-int virtio__get_dev_specific_field(int offset, bool msix, u32 *config_off);
+int virtio__get_dev_specific_field(int offset, u32 *config_off);
enum virtio_trans {
VIRTIO_PCI,
diff --git a/virtio/core.c b/virtio/core.c
index 90a661d1..afb09e90 100644
--- a/virtio/core.c
+++ b/virtio/core.c
@@ -169,16 +169,12 @@ void virtio_exit_vq(struct kvm *kvm, struct virtio_device *vdev,
memset(vq, 0, sizeof(*vq));
}
-int virtio__get_dev_specific_field(int offset, bool msix, u32 *config_off)
+int virtio__get_dev_specific_field(int offset, u32 *config_off)
{
- if (msix) {
- if (offset < 4)
- return VIRTIO_PCI_O_MSIX;
- else
- offset -= 4;
- }
+ if (offset < 24)
+ return VIRTIO_PCI_O_MSIX;
- *config_off = offset;
+ *config_off = offset - 24;
return VIRTIO_PCI_O_CONFIG;
}
diff --git a/virtio/pci.c b/virtio/pci.c
index eb91f512..2a6e41f1 100644
--- a/virtio/pci.c
+++ b/virtio/pci.c
@@ -112,9 +112,7 @@ static bool virtio_pci__specific_data_in(struct kvm *kvm, struct virtio_device *
{
u32 config_offset;
struct virtio_pci *vpci = vdev->virtio;
- int type = virtio__get_dev_specific_field(offset - 20,
- virtio_pci__msix_enabled(vpci),
- &config_offset);
+ int type = virtio__get_dev_specific_field(offset, &config_offset);
if (type == VIRTIO_PCI_O_MSIX) {
switch (offset) {
case VIRTIO_MSI_CONFIG_VECTOR:
@@ -208,8 +206,7 @@ static bool virtio_pci__specific_data_out(struct kvm *kvm, struct virtio_device
struct virtio_pci *vpci = vdev->virtio;
u32 config_offset, vec;
int gsi;
- int type = virtio__get_dev_specific_field(offset - 20, virtio_pci__msix_enabled(vpci),
- &config_offset);
+ int type = virtio__get_dev_specific_field(offset, &config_offset);
if (type == VIRTIO_PCI_O_MSIX) {
switch (offset) {
case VIRTIO_MSI_CONFIG_VECTOR:
--
2.30.2
