Re: [PATCH] x86/apic: check FADT settings after enable x2apic

[Yinghai Lu <yinghai@kernel.org>]

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On Tue, Jan 29, 2013 at 12:49 AM, Ingo Molnar <mingo@kernel.org> wrote:
>
> * Wang, Song-Bo (Stoney) <song-bo.wang@hp.com> wrote:
>
>> [...] Due to this mode mismatch, with specific HW
>> configurations, there will be intermittent lost interrupts,
>> which could result in a hang or data loss.
>
> That's the key piece of information that was missing - which
> should be put into the changelog into a very prominent place.
>
>> Logically, there is a mismatch because the kernel missed
>> detection on HW configurations, and we should fix it, right?
>> Do we need more detailed information?
>
> No, the above sentence is more than enough and the fix looks
> nice. Note that this sentence is more useful to users than the
> rest of the changelog combined!

Please check attached.

Thanks

Yinghai

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From:	Stoney Wang <song-bo.wang@hp.com>
Subject: [PATCH] x86, apic: Check fadt x2apic phys in x2apic_phys_probe()

When some HP sytems boot without x2apic_phys, there will be intermittent
lost interrupts and could result in a hang or data loss.

Those systems only work with x2apic phys mode so BIOS set
ACPI_FADT_APIC_PHYSICAL in FADT table.
Also because all apicids are less then 255, BIOS need to pass the control
to the OS with xapic mode, according to x2apic-spec, chapter 2.9.

Current code handle x2apic when BIOS pass with xapic mode:

When user specify x2apic_phys, or FADT indicates PHYSICAL.
During madt oem check, apic driver is set with xapic logical or
xapic phys driver at first.
Later enable_IR_x2apic() will enable x2apic_mode.
After that, x2apic_phys_probe() will install right x2apic phys driver
if user specify x2apic_phys,
but will skip and let x2apic_cluster_probe to take over to install
wrong apic driver (x2apic cluster) when FADT indicates
PHYSICAL, because x2apic_phys_probe does not check FADT PHYSICAL.

Add checking x2apic_fadt_phys in x2apic_phys_probe() to fix the problem.

-v3: update the change according to Ingo.

[ changelog, and simplify code - Yinghai Lu ]
Signed-off-by: Stoney Wang <song-bo.wang@hp.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>

---
 arch/x86/kernel/apic/x2apic_phys.c |   21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

Index: linux-2.6/arch/x86/kernel/apic/x2apic_phys.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/apic/x2apic_phys.c
+++ linux-2.6/arch/x86/kernel/apic/x2apic_phys.c
@@ -20,18 +20,19 @@ static int set_x2apic_phys_mode(char *ar
 }
 early_param("x2apic_phys", set_x2apic_phys_mode);
 
-static int x2apic_acpi_madt_oem_check(char *oem_id, char *oem_table_id)
+static bool x2apic_fadt_phys(void)
 {
-	if (x2apic_phys)
-		return x2apic_enabled();
-	else if ((acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID) &&
-		(acpi_gbl_FADT.flags & ACPI_FADT_APIC_PHYSICAL) &&
-		x2apic_enabled()) {
+	if ((acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID) &&
+		(acpi_gbl_FADT.flags & ACPI_FADT_APIC_PHYSICAL)) {
 		printk(KERN_DEBUG "System requires x2apic physical mode\n");
-		return 1;
+		return true;
 	}
-	else
-		return 0;
+	return false;
+}
+
+static int x2apic_acpi_madt_oem_check(char *oem_id, char *oem_table_id)
+{
+	return x2apic_enabled() && (x2apic_phys || x2apic_fadt_phys());
 }
 
 static void
@@ -82,7 +83,7 @@ static void init_x2apic_ldr(void)
 
 static int x2apic_phys_probe(void)
 {
-	if (x2apic_mode && x2apic_phys)
+	if (x2apic_mode && (x2apic_phys || x2apic_fadt_phys()))
 		return 1;
 
 	return apic == &apic_x2apic_phys;