[PATCH 1/2] x86/xen/apic: Work with UP, non-SMP 32-bit kernels.

[Konrad Rzeszutek Wilk]

Most of the APIC code that use APIC_LDR is not used on
64-bit. On 32-bit it is bit of an hack - and the mechanism
it is uses is to "setup" the APIC_LDR via apci->init_apic_ldr
(which we set to NULL) and then use apic->x86_32_early_logical_apicid
to get an CPU to APIC ID mapping and also apic->read to match
the APIC_LDR.

The 'x86_32_early_logical_apicid' is called from 'setup_local_APIC'
which is called from the following functions:
 - start_secondary ->smp_callin -> apic_ap_setup [not called on PV]
 - native_smp_prepare_cpus -> apci_bsp_setup [not called on PV]
 - up_late_init -> APIC_init_uniprocessor -> apic_bsp_setup ->setup_local_APIC
   [called on PV with CONFIG_SMP not defined, CONFIG_X86_32 and UP kernel]

This patch fixes the build issue and also allows the bootup
to continue without warnings.

Reported-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 arch/x86/xen/apic.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/x86/xen/apic.c b/arch/x86/xen/apic.c
index 86bea3e..de1c74d 100644
--- a/arch/x86/xen/apic.c
+++ b/arch/x86/xen/apic.c
@@ -56,7 +56,10 @@ static u32 xen_apic_read(u32 reg)
 
 	if (reg == APIC_LVR)
 		return 0x10;
-
+#ifdef CONFIG_X86_32
+	if (reg == APIC_LDR)
+		return SET_APIC_LOGICAL_ID(1UL << smp_processor_id());
+#endif
 	if (reg != APIC_ID)
 		return 0;
 
@@ -117,6 +120,12 @@ static int xen_phys_pkg_id(int initial_apic_id, int index_msb)
 	return initial_apic_id >> index_msb;
 }
 
+static int xen_x86_32_early_logical_apicid(int cpu)
+{
+	/* Match with APIC_LDR read. Otherwise setup_local_APIC complains. */
+	return 1 << cpu;
+}
+
 static void xen_noop(void)
 {
 }
@@ -176,8 +185,8 @@ static struct apic xen_pv_apic = {
 	.safe_wait_icr_idle 		= xen_safe_apic_wait_icr_idle,
 
 #ifdef CONFIG_X86_32
-	/* generic_processor_info */
-	.x86_32_early_logical_apicid	= default_x86_32_early_logical_apicid,
+	/* generic_processor_info and setup_local_APIC. */
+	.x86_32_early_logical_apicid	= xen_x86_32_early_logical_apicid,
 #endif
 };
 
-- 
1.8.4.2

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