[Xen-devel] [RFC PATCH] xen, apic: Setup our own APIC criver and validator for APIC IDs.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

Via CPUID masking and the different apic-> overrides we
effectively make PV guests only but with the default APIC
driver. That is OK as an PV guest should never access any
APIC registers. However, the APIC is also used to limit the
amount of CPUs if the APIC IDs are incorrect - and since we
mask the x2APIC from the CPUID - any APIC IDs above 0xFF
are deemed incorrect by the default APIC routines.

As such add a new routine to check for APIC ID which will
be only used if the CPUID (native one) tells us the system
is using x2APIC.

This allows us to boot with more than 255 CPUs if running
as initial domain.

Reported-by: Cathy Avery <cathy.avery@xxxxxxxxxx>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 arch/x86/xen/enlighten.c | 79 +++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 64 insertions(+), 15 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 6bf3a13..84d979e 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -989,27 +989,76 @@ static u32 xen_safe_apic_wait_icr_idle(void)
         return 0;
 }
 
-static void set_xen_basic_apic_ops(void)
+
+static int probe_xen(void)
 {
-       apic->read = xen_apic_read;
-       apic->write = xen_apic_write;
-       apic->icr_read = xen_apic_icr_read;
-       apic->icr_write = xen_apic_icr_write;
-       apic->wait_icr_idle = xen_apic_wait_icr_idle;
-       apic->safe_wait_icr_idle = xen_safe_apic_wait_icr_idle;
-       apic->set_apic_id = xen_set_apic_id;
-       apic->get_apic_id = xen_get_apic_id;
+       if (!xen_initial_domain())
+               return 0;
 
-#ifdef CONFIG_SMP
-       apic->send_IPI_allbutself = xen_send_IPI_allbutself;
-       apic->send_IPI_mask_allbutself = xen_send_IPI_mask_allbutself;
-       apic->send_IPI_mask = xen_send_IPI_mask;
-       apic->send_IPI_all = xen_send_IPI_all;
-       apic->send_IPI_self = xen_send_IPI_self;
+       return 1;
+}
+
+static int id_valid_xen(int apicid)
+{
+       return 1;
+}
+
+static struct apic xen_null_apic = {
+       .name = "Xen",
+       .probe = probe_xen,
+       /* The rest is copied from the default. */
+};
+
+/*
+ * This is needed as in enlighten.c we mask the x2APIC bit because we
+ * do not want PV guests to use anything but the default apic routines
+ * (which have an abstraction layer that we use).
+ *
+ * However the default ->apic_id_valid enforces that the APIC ID MUST
+ * be below 0xFF which is not the case for x2APIC - so we need a way
+ * to allow that to function.
+ */
+static bool __init xen_check_x2apic(void)
+{
+#ifdef CONFIG_X2APIC
+       unsigned int ax, bx, cx, dx;
+
+       ax = 1;
+       cx = 0; /* Don't care about dx, and bx */
+       native_cpuid(&ax, &bx, &cx, &dx);
+       if (cx & (1 << (X86_FEATURE_X2APIC % 32)))
+               return true;
 #endif
+       return false;
 }
 
+void __init set_xen_basic_apic_ops(void)
+{
+       memcpy(&xen_null_apic, apic, sizeof(struct apic));
+       xen_null_apic.probe = probe_xen;
+       xen_null_apic.name = "Xen";
+
+       xen_null_apic.read = xen_apic_read;
+       xen_null_apic.write = xen_apic_write;
+       xen_null_apic.icr_read = xen_apic_icr_read;
+       xen_null_apic.icr_write = xen_apic_icr_write;
+       xen_null_apic.wait_icr_idle = xen_apic_wait_icr_idle;
+       xen_null_apic.safe_wait_icr_idle = xen_safe_apic_wait_icr_idle;
+       xen_null_apic.set_apic_id = xen_set_apic_id;
+       xen_null_apic.get_apic_id = xen_get_apic_id;
+
+       xen_null_apic.send_IPI_allbutself = xen_send_IPI_allbutself;
+       xen_null_apic.send_IPI_mask_allbutself = xen_send_IPI_mask_allbutself;
+       xen_null_apic.send_IPI_mask = xen_send_IPI_mask;
+       xen_null_apic.send_IPI_all = xen_send_IPI_all;
+       xen_null_apic.send_IPI_self = xen_send_IPI_self;
 #endif
+       if (xen_check_x2apic()) {
+               printk(KERN_INFO "Xen: Using x2APIC!\n");
+               xen_null_apic.apic_id_valid = id_valid_xen;
+       }
+}
+apic_driver(xen_null_apic);
 
 static void xen_clts(void)
 {
-- 
2.1.0


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