[PATCH v3] xen: Remove dependency between pciback and privcmd

[Jiqian Chen <Jiqian.Chen@xxxxxxx>]

Commit 2fae6bb7be32 ("xen/privcmd: Add new syscall to get gsi from dev")
adds a weak reverse dependency to the config XEN_PRIVCMD definition, that
dependency causes xen-privcmd can't be loaded on domU, because dependent
xen-pciback isn't always be loaded successfully on domU.

To solve above problem, remove that dependency, and do not call
pcistub_get_gsi_from_sbdf() directly, instead add a hook in
drivers/xen/apci.c, xen-pciback register the real call function, then in
privcmd_ioctl_pcidev_get_gsi call that hook.

Fixes: 2fae6bb7be32 ("xen/privcmd: Add new syscall to get gsi from dev")
Reported-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
---
v2->v3 changes:
Added rwlock get_gsi_from_sbdf_lock to avoid races.
Called xen_acpi_register_get_gsi_func to register function in xen_pcibk_init 
and set NULL to hook in xen_pcibk_cleanup when unloading.

v1->v2 changes:
Added hook xen_acpi_get_gsi_from_sbdf.
Changed pcistub_get_gsi_from_sbdf to static and pciback register it as the real 
hook function.
---
 drivers/xen/Kconfig                |  1 -
 drivers/xen/acpi.c                 | 24 ++++++++++++++++++++++++
 drivers/xen/privcmd.c              |  6 ++----
 drivers/xen/xen-pciback/pci_stub.c | 11 +++++++++--
 include/xen/acpi.h                 | 12 ++++--------
 5 files changed, 39 insertions(+), 15 deletions(-)

diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index 72ddee4c1544..f7d6f47971fd 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -261,7 +261,6 @@ config XEN_SCSI_BACKEND
 config XEN_PRIVCMD
        tristate "Xen hypercall passthrough driver"
        depends on XEN
-       imply XEN_PCIDEV_BACKEND
        default m
        help
          The hypercall passthrough driver allows privileged user programs to
diff --git a/drivers/xen/acpi.c b/drivers/xen/acpi.c
index 9e2096524fbc..d2ee605c5ca1 100644
--- a/drivers/xen/acpi.c
+++ b/drivers/xen/acpi.c
@@ -125,3 +125,27 @@ int xen_acpi_get_gsi_info(struct pci_dev *dev,
        return 0;
 }
 EXPORT_SYMBOL_GPL(xen_acpi_get_gsi_info);
+
+static get_gsi_from_sbdf_t get_gsi_from_sbdf;
+static DEFINE_RWLOCK(get_gsi_from_sbdf_lock);
+
+void xen_acpi_register_get_gsi_func(get_gsi_from_sbdf_t func)
+{
+       write_lock(&get_gsi_from_sbdf_lock);
+       get_gsi_from_sbdf = func;
+       write_unlock(&get_gsi_from_sbdf_lock);
+}
+EXPORT_SYMBOL_GPL(xen_acpi_register_get_gsi_func);
+
+int xen_acpi_get_gsi_from_sbdf(u32 sbdf)
+{
+       int ret = -EOPNOTSUPP;
+
+       read_lock(&get_gsi_from_sbdf_lock);
+       if (get_gsi_from_sbdf)
+               ret = get_gsi_from_sbdf(sbdf);
+       read_unlock(&get_gsi_from_sbdf_lock);
+
+       return ret;
+}
+EXPORT_SYMBOL_GPL(xen_acpi_get_gsi_from_sbdf);
diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index 3273cb8c2a66..4f75bc876454 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -850,15 +850,13 @@ static long privcmd_ioctl_mmap_resource(struct file *file,
 static long privcmd_ioctl_pcidev_get_gsi(struct file *file, void __user *udata)
 {
 #if defined(CONFIG_XEN_ACPI)
-       int rc = -EINVAL;
+       int rc;
        struct privcmd_pcidev_get_gsi kdata;
 
        if (copy_from_user(&kdata, udata, sizeof(kdata)))
                return -EFAULT;
 
-       if (IS_REACHABLE(CONFIG_XEN_PCIDEV_BACKEND))
-               rc = pcistub_get_gsi_from_sbdf(kdata.sbdf);
-
+       rc = xen_acpi_get_gsi_from_sbdf(kdata.sbdf);
        if (rc < 0)
                return rc;
 
diff --git a/drivers/xen/xen-pciback/pci_stub.c 
b/drivers/xen/xen-pciback/pci_stub.c
index 2f3da5ac62cd..b616b7768c3b 100644
--- a/drivers/xen/xen-pciback/pci_stub.c
+++ b/drivers/xen/xen-pciback/pci_stub.c
@@ -227,7 +227,7 @@ static struct pci_dev *pcistub_device_get_pci_dev(struct 
xen_pcibk_device *pdev,
 }
 
 #ifdef CONFIG_XEN_ACPI
-int pcistub_get_gsi_from_sbdf(unsigned int sbdf)
+static int pcistub_get_gsi_from_sbdf(unsigned int sbdf)
 {
        struct pcistub_device *psdev;
        int domain = (sbdf >> 16) & 0xffff;
@@ -242,7 +242,6 @@ int pcistub_get_gsi_from_sbdf(unsigned int sbdf)
 
        return psdev->gsi;
 }
-EXPORT_SYMBOL_GPL(pcistub_get_gsi_from_sbdf);
 #endif
 
 struct pci_dev *pcistub_get_pci_dev_by_slot(struct xen_pcibk_device *pdev,
@@ -1757,11 +1756,19 @@ static int __init xen_pcibk_init(void)
                bus_register_notifier(&pci_bus_type, &pci_stub_nb);
 #endif
 
+#ifdef CONFIG_XEN_ACPI
+       xen_acpi_register_get_gsi_func(pcistub_get_gsi_from_sbdf);
+#endif
+
        return err;
 }
 
 static void __exit xen_pcibk_cleanup(void)
 {
+#ifdef CONFIG_XEN_ACPI
+       xen_acpi_register_get_gsi_func(NULL);
+#endif
+
 #ifdef CONFIG_PCI_IOV
        bus_unregister_notifier(&pci_bus_type, &pci_stub_nb);
 #endif
diff --git a/include/xen/acpi.h b/include/xen/acpi.h
index daa96a22d257..8cb081c633cc 100644
--- a/include/xen/acpi.h
+++ b/include/xen/acpi.h
@@ -91,13 +91,9 @@ static inline int xen_acpi_get_gsi_info(struct pci_dev *dev,
 }
 #endif
 
-#ifdef CONFIG_XEN_PCI_STUB
-int pcistub_get_gsi_from_sbdf(unsigned int sbdf);
-#else
-static inline int pcistub_get_gsi_from_sbdf(unsigned int sbdf)
-{
-       return -1;
-}
-#endif
+typedef int (*get_gsi_from_sbdf_t)(u32 sbdf);
+
+void xen_acpi_register_get_gsi_func(get_gsi_from_sbdf_t func);
+int xen_acpi_get_gsi_from_sbdf(u32 sbdf);
 
 #endif /* _XEN_ACPI_H */
-- 
2.34.1