diff options
| author | David Woodhouse <dwmw@amazon.co.uk> | 2020-10-24 22:35:01 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-12-30 11:25:50 +0100 |
| commit | a3ad889a4557159123aceaf74465b890d34b1109 (patch) | |
| tree | e7bd51f6ddb8ae981e92b6551022e35275b24fcc /arch/x86/kernel/apic/apic.c | |
| parent | ecc3960efd13003636238fe877f272f7cadd1707 (diff) | |
| download | linux-stable-a3ad889a4557159123aceaf74465b890d34b1109.tar.gz | |
x86/apic: Fix x2apic enablement without interrupt remapping
[ Upstream commit 26573a97746c7a99f394f9d398ce91a8853b3b89 ]
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: ce69a784504 ("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
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'arch/x86/kernel/apic/apic.c')
| -rw-r--r-- | arch/x86/kernel/apic/apic.c | 14 |
1 files changed, 8 insertions, 6 deletions
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c index e9456a2eef58..ab8187271d47 100644 --- a/arch/x86/kernel/apic/apic.c +++ b/arch/x86/kernel/apic/apic.c @@ -1813,20 +1813,22 @@ 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(); |