[RFC 09/13] vfio/pci: introduce CXL device awareness

Zhi Wang
2024-09-20T22:35:19Z

CXL device programming interfaces are built upon PCI interfaces. Thus
the vfio-pci-core can be leveraged to handle a CXL device.

However, CXL device also has difference with PCI devicce:

- No INTX support, only MSI/MSIX is supported.
- Resest is one via CXL reset. FLR only resets CXL.io.

Introduce the CXL device awareness to the vfio-pci-core. Expose a new
VFIO device flags to the userspace to identify the VFIO device is a CXL
device. Disable INTX support in the vfio-pci-core. Disable FLR reset for
the CXL device as the kernel CXL core hasn't support CXL reset yet.
Disable mmap support on the CXL MMIO BAR in vfio-pci-core.

Signed-off-by: Zhi Wang <zhiw@nvidia.com>
---
drivers/vfio/pci/vfio_cxl_core.c | 8 ++++++
drivers/vfio/pci/vfio_pci_core.c | 42 +++++++++++++++++++++-----------
include/linux/vfio_pci_core.h | 2 ++
include/uapi/linux/vfio.h | 1 +
4 files changed, 39 insertions(+), 14 deletions(-)

diff --git a/drivers/vfio/pci/vfio_cxl_core.c b/drivers/vfio/pci/vfio_cxl_core.c
index bbb968cb1b70..d8b51f8792a2 100644
--- a/drivers/vfio/pci/vfio_cxl_core.c
+++ b/drivers/vfio/pci/vfio_cxl_core.c
@@ -391,6 +391,8 @@ int vfio_cxl_core_enable(struct vfio_pci_core_device *core_dev)
if (ret)
return ret;

+ vfio_pci_core_enable_cxl(core_dev);
+
ret = vfio_pci_core_enable(core_dev);
if (ret)
goto err_pci_core_enable;
@@ -618,6 +620,12 @@ ssize_t vfio_cxl_core_write(struct vfio_device *core_vdev, const char __user *bu
}
EXPORT_SYMBOL_GPL(vfio_cxl_core_write);

+void vfio_pci_core_enable_cxl(struct vfio_pci_core_device *core_dev)
+{
+ core_dev->has_cxl = true;
+}
+EXPORT_SYMBOL(vfio_pci_core_enable_cxl);
+
MODULE_LICENSE("GPL");
MODULE_AUTHOR(DRIVER_AUTHOR);
MODULE_DESCRIPTION(DRIVER_DESC);
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 9373942f1acb..e0f23b538858 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -126,6 +126,9 @@ static void vfio_pci_probe_mmaps(struct vfio_pci_core_device *vdev)
if (!(res->flags & IORESOURCE_MEM))
goto no_mmap;

+ if (vdev->has_cxl && bar == vdev->cxl.comp_reg_bar)
+ goto no_mmap;
+
/*
* The PCI core shouldn't set up a resource with a
* type but zero size. But there may be bugs that
@@ -487,10 +490,15 @@ int vfio_pci_core_enable(struct vfio_pci_core_device *vdev)
if (ret)
goto out_power;

- /* If reset fails because of the device lock, fail this path entirely */
- ret = pci_try_reset_function(pdev);
- if (ret == -EAGAIN)
- goto out_disable_device;
+ if (!vdev->has_cxl) {
+ /* If reset fails because of the device lock, fail this path entirely */
+ ret = pci_try_reset_function(pdev);
+ if (ret == -EAGAIN)
+ goto out_disable_device;
+ } else {
+ /* CXL Reset is missing in CXL core. FLR only resets CXL.io path. */
+ ret = -ENODEV;
+ }

vdev->reset_works = !ret;
pci_save_state(pdev);
@@ -498,14 +506,17 @@ int vfio_pci_core_enable(struct vfio_pci_core_device *vdev)
if (!vdev->pci_saved_state)
pci_dbg(pdev, "%s: Couldn't store saved state\n", __func__);

- if (likely(!nointxmask)) {
- if (vfio_pci_nointx(pdev)) {
- pci_info(pdev, "Masking broken INTx support\n");
- vdev->nointx = true;
- pci_intx(pdev, 0);
- } else
- vdev->pci_2_3 = pci_intx_mask_supported(pdev);
- }
+ if (!vdev->has_cxl) {
+ if (likely(!nointxmask)) {
+ if (vfio_pci_nointx(pdev)) {
+ pci_info(pdev, "Masking broken INTx support\n");
+ vdev->nointx = true;
+ pci_intx(pdev, 0);
+ } else
+ vdev->pci_2_3 = pci_intx_mask_supported(pdev);
+ }
+ } else
+ vdev->nointx = true; /* CXL device doesn't have INTX. */

pci_read_config_word(pdev, PCI_COMMAND, &cmd);
if (vdev->pci_2_3 && (cmd & PCI_COMMAND_INTX_DISABLE)) {
@@ -541,7 +552,6 @@ int vfio_pci_core_enable(struct vfio_pci_core_device *vdev)
if (!vfio_vga_disabled() && vfio_pci_is_vga(pdev))
vdev->has_vga = true;

-
return 0;

out_free_zdev:
@@ -657,7 +667,8 @@ void vfio_pci_core_disable(struct vfio_pci_core_device *vdev)
* Disable INTx and MSI, presumably to avoid spurious interrupts
* during reset. Stolen from pci_reset_function()
*/
- pci_write_config_word(pdev, PCI_COMMAND, PCI_COMMAND_INTX_DISABLE);
+ if (!vdev->nointx)
+ pci_write_config_word(pdev, PCI_COMMAND, PCI_COMMAND_INTX_DISABLE);

/*
* Try to get the locks ourselves to prevent a deadlock. The
@@ -973,6 +984,9 @@ static int vfio_pci_ioctl_get_info(struct vfio_pci_core_device *vdev,
if (vdev->reset_works)
info.flags |= VFIO_DEVICE_FLAGS_RESET;

+ if (vdev->has_cxl)
+ info.flags |= VFIO_DEVICE_FLAGS_CXL;
+
info.num_regions = VFIO_PCI_NUM_REGIONS + vdev->num_regions;
info.num_irqs = VFIO_PCI_NUM_IRQS;

diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
index 9d295ca9382a..e5646aad3eb3 100644
--- a/include/linux/vfio_pci_core.h
+++ b/include/linux/vfio_pci_core.h
@@ -113,6 +113,7 @@ struct vfio_pci_core_device {
bool needs_pm_restore:1;
bool pm_intx_masked:1;
bool pm_runtime_engaged:1;
+ bool has_cxl:1;
struct pci_saved_state *pci_saved_state;
struct pci_saved_state *pm_save;
int ioeventfds_nr;
@@ -208,5 +209,6 @@ ssize_t vfio_cxl_core_read(struct vfio_device *core_vdev, char __user *buf,
size_t count, loff_t *ppos);
ssize_t vfio_cxl_core_write(struct vfio_device *core_vdev, const char __user *buf,
size_t count, loff_t *ppos);
+void vfio_pci_core_enable_cxl(struct vfio_pci_core_device *core_dev);

#endif /* VFIO_PCI_CORE_H */
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 71f766c29060..0895183feaac 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -214,6 +214,7 @@ struct vfio_device_info {
#define VFIO_DEVICE_FLAGS_FSL_MC (1 << 6) /* vfio-fsl-mc device */
#define VFIO_DEVICE_FLAGS_CAPS (1 << 7) /* Info supports caps */
#define VFIO_DEVICE_FLAGS_CDX (1 << 8) /* vfio-cdx device */
+#define VFIO_DEVICE_FLAGS_CXL (1 << 9) /* Device supports CXL support */
__u32 num_regions; /* Max region index + 1 */
__u32 num_irqs; /* Max IRQ index + 1 */
__u32 cap_offset; /* Offset within info struct of first cap */
--
2.34.1