Commit e211288b authored Oct 10, 2019 by Roman Kagan Committed by Thomas Gleixner Oct 15, 2019

x86/hyperv: Make vapic support x2apic mode



Now that there's Hyper-V IOMMU driver, Linux can switch to x2apic mode
when supported by the vcpus.

However, the apic access functions for Hyper-V enlightened apic assume
xapic mode only.

As a result, Linux fails to bring up secondary cpus when run as a guest
in QEMU/KVM with both hv_apic and x2apic enabled.

According to Michael Kelley, when in x2apic mode, the Hyper-V synthetic
apic MSRs behave exactly the same as the corresponding architectural
x2apic MSRs, so there's no need to override the apic accessors.  The
only exception is hv_apic_eoi_write, which benefits from lazy EOI when
available; however, its implementation works for both xapic and x2apic
modes.

Fixes: 29217a47 ("iommu/hyper-v: Add Hyper-V stub IOMMU driver")
Fixes: 6b48cb5f ("X86/Hyper-V: Enlighten APIC access")
Suggested-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Roman Kagan <rkagan@virtuozzo.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20191010123258.16919-1-rkagan@virtuozzo.com

parent 1869dbe8

arch/x86/hyperv/hv_apic.c

+15 −5

Original line number	Diff line number	Diff line
		@@ -260,11 +260,21 @@ void __init hv_apic_init(void)
		}

		if (ms_hyperv.hints & HV_X64_APIC_ACCESS_RECOMMENDED) {
		pr_info("Hyper-V: Using MSR based APIC access\n");
		pr_info("Hyper-V: Using enlightened APIC (%s mode)",
		x2apic_enabled() ? "x2apic" : "xapic");
		/*
		* With x2apic, architectural x2apic MSRs are equivalent to the
		* respective synthetic MSRs, so there's no need to override
		* the apic accessors. The only exception is
		* hv_apic_eoi_write, because it benefits from lazy EOI when
		* available, but it works for both xapic and x2apic modes.
		*/
		apic_set_eoi_write(hv_apic_eoi_write);
		if (!x2apic_enabled()) {
		apic->read = hv_apic_read;
		apic->write = hv_apic_write;
		apic->icr_write = hv_apic_icr_write;
		apic->icr_read = hv_apic_icr_read;
		}
		}
		}

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