[PATCH 3/3] usb: xhci: Notify xen when DbC is unsafe to use

[Connor Davis <connojdavis@xxxxxxxxx>]

When running as a dom0 guest on Xen, check if the USB3 debug
capability is enabled before xHCI reset, suspend, and resume. If it
is, call xen_dbgp_reset_prep() to notify Xen that it is unsafe to touch
MMIO registers until the next xen_dbgp_external_startup().

This notification allows Xen to avoid undefined behavior resulting
from MMIO access when the host controller's CNR bit is set or when
the device transitions to D3hot.

Signed-off-by: Connor Davis <connojdavis@xxxxxxxxx>
---
 drivers/usb/host/xhci-dbgcap.h |  6 ++++
 drivers/usb/host/xhci.c        | 57 ++++++++++++++++++++++++++++++++++
 drivers/usb/host/xhci.h        |  1 +
 3 files changed, 64 insertions(+)

diff --git a/drivers/usb/host/xhci-dbgcap.h b/drivers/usb/host/xhci-dbgcap.h
index c70b78d504eb..24784b82a840 100644
--- a/drivers/usb/host/xhci-dbgcap.h
+++ b/drivers/usb/host/xhci-dbgcap.h
@@ -227,4 +227,10 @@ static inline int xhci_dbc_resume(struct xhci_hcd *xhci)
        return 0;
 }
 #endif /* CONFIG_USB_XHCI_DBGCAP */
+
+#ifdef CONFIG_XEN_DOM0
+int xen_dbgp_reset_prep(struct usb_hcd *hcd);
+int xen_dbgp_external_startup(struct usb_hcd *hcd);
+#endif /* CONFIG_XEN_DOM0 */
+
 #endif /* __LINUX_XHCI_DBGCAP_H */
diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index ca9385d22f68..afe44169183f 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -37,6 +37,57 @@ static unsigned long long quirks;
 module_param(quirks, ullong, S_IRUGO);
 MODULE_PARM_DESC(quirks, "Bit flags for quirks to be enabled as default");

+#ifdef CONFIG_XEN_DOM0
+#include <xen/xen.h>
+
+static void xhci_dbc_external_reset_prep(struct xhci_hcd *xhci)
+{
+       struct dbc_regs __iomem *regs;
+       void __iomem            *base;
+       int                     dbc_cap;
+
+       if (!xen_initial_domain())
+               return;
+
+       base = &xhci->cap_regs->hc_capbase;
+       dbc_cap = xhci_find_next_ext_cap(base, 0, XHCI_EXT_CAPS_DEBUG);
+
+       if (!dbc_cap)
+               return;
+
+       xhci->external_dbc = 0;
+       regs = base + dbc_cap;
+
+       if (readl(&regs->control) & DBC_CTRL_DBC_ENABLE) {
+               if (xen_dbgp_reset_prep(xhci_to_hcd(xhci)))
+                       xhci_dbg_trace(xhci, trace_xhci_dbg_init,
+                                       "// Failed to reset external DBC");
+               else {
+                       xhci->external_dbc = 1;
+                       xhci_dbg_trace(xhci, trace_xhci_dbg_init,
+                                       "// Completed reset of external DBC");
+               }
+       }
+}
+
+static void xhci_dbc_external_reset_done(struct xhci_hcd *xhci)
+{
+       if (!xen_initial_domain() || !xhci->external_dbc)
+               return;
+
+       if (xen_dbgp_external_startup(xhci_to_hcd(xhci)))
+               xhci->external_dbc = 0;
+}
+#else
+static void xhci_dbc_external_reset_prep(struct xhci_hcd *xhci)
+{
+}
+
+static void xhci_dbc_external_reset_done(struct xhci_hcd *xhci)
+{
+}
+#endif
+
 static bool td_on_ring(struct xhci_td *td, struct xhci_ring *ring)
 {
        struct xhci_segment *seg = ring->first_seg;
@@ -180,6 +231,8 @@ int xhci_reset(struct xhci_hcd *xhci)
                return 0;
        }

+       xhci_dbc_external_reset_prep(xhci);
+
        xhci_dbg_trace(xhci, trace_xhci_dbg_init, "// Reset the HC");
        command = readl(&xhci->op_regs->command);
        command |= CMD_RESET;
@@ -211,6 +264,8 @@ int xhci_reset(struct xhci_hcd *xhci)
         */
        ret = xhci_handshake(&xhci->op_regs->status,
                        STS_CNR, 0, 10 * 1000 * 1000);
+       if (!ret)
+               xhci_dbc_external_reset_done(xhci);

        xhci->usb2_rhub.bus_state.port_c_suspend = 0;
        xhci->usb2_rhub.bus_state.suspended_ports = 0;
@@ -991,6 +1046,7 @@ int xhci_suspend(struct xhci_hcd *xhci, bool do_wakeup)
                return 0;

        xhci_dbc_suspend(xhci);
+       xhci_dbc_external_reset_prep(xhci);

        /* Don't poll the roothubs on bus suspend. */
        xhci_dbg(xhci, "%s: stopping port polling.\n", __func__);
@@ -1225,6 +1281,7 @@ int xhci_resume(struct xhci_hcd *xhci, bool hibernated)
        spin_unlock_irq(&xhci->lock);

        xhci_dbc_resume(xhci);
+       xhci_dbc_external_reset_done(xhci);

  done:
        if (retval == 0) {
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index 2595a8f057c4..61d8efc9eef2 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1920,6 +1920,7 @@ struct xhci_hcd {
        struct list_head        regset_list;

        void                    *dbc;
+       int                     external_dbc;
        /* platform-specific data -- must come last */
        unsigned long           priv[] __aligned(sizeof(s64));
 };
--
2.31.1