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x86/apic: Fix x2apic enablement without interrupt remapping

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Currently, Linux as a hypervisor guest will enable x2apic only if there are
no CPUs present at boot time with an APIC ID above 255.

Hotplugging a CPU later with a higher APIC ID would result in a CPU which
cannot be targeted by external interrupts.

Add a filter in x2apic_apic_id_valid() which can be used to prevent such
CPUs from coming online, and allow x2apic to be enabled even if they are
present at boot time.

Fixes: ce69a78450 ("x86/apic: Enable x2APIC without interrupt remapping under KVM")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20201024213535.443185-2-dwmw2@infradead.org
This commit is contained in:
David Woodhouse 2020-10-24 22:35:01 +01:00 committed by Thomas Gleixner
parent 5a169bf04c
commit 26573a9774
3 changed files with 18 additions and 6 deletions
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1
arch/x86/include/asm/apic.h
View File

@ -259,6 +259,7 @@ static inline u64 native_x2apic_icr_read(void)
extern int x2apic_mode;
extern int x2apic_phys;
extern void __init x2apic_set_max_apicid(u32 apicid);
extern void __init check_x2apic(void);
extern void x2apic_setup(void);
static inline int x2apic_enabled(void)

14
arch/x86/kernel/apic/apic.c
View File

@ -1841,20 +1841,22 @@ static __init void try_to_enable_x2apic(int remap_mode)
return;
if (remap_mode != IRQ_REMAP_X2APIC_MODE) {
/* IR is required if there is APIC ID > 255 even when running
* under KVM
/*
* Using X2APIC without IR is not architecturally supported
* on bare metal but may be supported in guests.
*/
if (max_physical_apicid > 255 ||
!x86_init.hyper.x2apic_available()) {
if (!x86_init.hyper.x2apic_available()) {
pr_info("x2apic: IRQ remapping doesn't support X2APIC mode\n");
x2apic_disable();
return;
}
/*
* without IR all CPUs can be addressed by IOAPIC/MSI
* only in physical mode
* Without IR, all CPUs can be addressed by IOAPIC/MSI only
* in physical mode, and CPUs with an APIC ID that cannnot
* be addressed must not be brought online.
*/
x2apic_set_max_apicid(255);
x2apic_phys = 1;
}
x2apic_enable();

9
arch/x86/kernel/apic/x2apic_phys.c
View File

@ -8,6 +8,12 @@
int x2apic_phys;
static struct apic apic_x2apic_phys;
static u32 x2apic_max_apicid __ro_after_init;
void __init x2apic_set_max_apicid(u32 apicid)
{
x2apic_max_apicid = apicid;
}
static int __init set_x2apic_phys_mode(char *arg)
{
@ -98,6 +104,9 @@ static int x2apic_phys_probe(void)
/* Common x2apic functions, also used by x2apic_cluster */
int x2apic_apic_id_valid(u32 apicid)
{
if (x2apic_max_apicid && apicid > x2apic_max_apicid)
return 0;
return 1;
}