[PATCH AUTOSEL 5.4 15/26] x86/xen: Add xen_no_vector_callback option to test PCI INTX delivery

[Sasha Levin <sashal@xxxxxxxxxx>]

From: David Woodhouse <dwmw@xxxxxxxxxxxx>

[ Upstream commit b36b0fe96af13460278bf9b173beced1bd15f85d ]

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>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20210106153958.584169-4-dwmw2@xxxxxxxxxxxxx
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 74ba077e99e56..a19ae163c0589 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5452,6 +5452,10 @@
                        This option is obsoleted by the "nopv" option, which
                        has equivalent effect for XEN platform.
 
+       xen_no_vector_callback
+                       [KNL,X86,XEN] Disable the vector callback for Xen
+                       event channel interrupts.
+
        xen_scrub_pages=        [XEN]
                        Boolean option to control scrubbing pages before giving 
them back
                        to Xen, for use by other domains. Can be also changed 
at runtime
diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
index e138f7de52d20..6024fafed1642 100644
--- a/arch/x86/xen/enlighten_hvm.c
+++ b/arch/x86/xen/enlighten_hvm.c
@@ -175,6 +175,8 @@ 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())
@@ -194,7 +196,7 @@ 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();
@@ -220,6 +222,13 @@ 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("xen_no_vector_callback", xen_parse_no_vector_callback);
+
 bool __init xen_hvm_need_lapic(void)
 {
        if (xen_pv_domain())
-- 
2.27.0