[PATCH v2 3/5] x86/xen: Add a no_vector_callback option to test PCI INTX delivery

[David Woodhouse <dwmw2@xxxxxxxxxxxxx>]

From: David Woodhouse <dwmw@xxxxxxxxxxxx>

It's useful to be able to test non-vector event channel delivery, to make
sure Linux will work properly on older Xen which doesn't have it.

It's also useful for those working on Xen and Xen-compatible hypervisors,
because there are guest kernels still in active use which use PCI INTX
even when vector delivery is available.

Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
---
 Documentation/admin-guide/kernel-parameters.txt |  4 ++++
 arch/x86/xen/enlighten_hvm.c                    | 11 ++++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt 
b/Documentation/admin-guide/kernel-parameters.txt
index c722ec19cd00..35b10982d363 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3389,6 +3389,10 @@
 
        nosync          [HW,M68K] Disables sync negotiation for all devices.
 
+       no_vector_callback
+                       [KNL,X86,XEN] Disable the vector callback for Xen
+                       event channel interrupts.
+
        nowatchdog      [KNL] Disable both lockup detectors, i.e.
                        soft-lockup and NMI watchdog (hard-lockup).
 
diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
index 9e87ab010c82..a1c07e0c888e 100644
--- a/arch/x86/xen/enlighten_hvm.c
+++ b/arch/x86/xen/enlighten_hvm.c
@@ -188,6 +188,8 @@ static int xen_cpu_dead_hvm(unsigned int cpu)
        return 0;
 }
 
+static bool no_vector_callback __initdata;
+
 static void __init xen_hvm_guest_init(void)
 {
        if (xen_pv_domain())
@@ -207,7 +209,7 @@ static void __init xen_hvm_guest_init(void)
 
        xen_panic_handler_init();
 
-       if (xen_feature(XENFEAT_hvm_callback_vector))
+       if (!no_vector_callback && xen_feature(XENFEAT_hvm_callback_vector))
                xen_have_vector_callback = 1;
 
        xen_hvm_smp_init();
@@ -233,6 +235,13 @@ static __init int xen_parse_nopv(char *arg)
 }
 early_param("xen_nopv", xen_parse_nopv);
 
+static __init int xen_parse_no_vector_callback(char *arg)
+{
+       no_vector_callback = true;
+       return 0;
+}
+early_param("no_vector_callback", xen_parse_no_vector_callback);
+
 bool __init xen_hvm_need_lapic(void)
 {
        if (xen_pv_domain())
-- 
2.29.2