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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:29217a4746
("iommu/hyper-v: Add Hyper-V stub IOMMU driver") Fixes:6b48cb5f83
("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
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1 changed files with 15 additions and 5 deletions
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@ -260,11 +260,21 @@ void __init hv_apic_init(void)
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}
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if (ms_hyperv.hints & HV_X64_APIC_ACCESS_RECOMMENDED) {
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pr_info("Hyper-V: Using MSR based APIC access\n");
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pr_info("Hyper-V: Using enlightened APIC (%s mode)",
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x2apic_enabled() ? "x2apic" : "xapic");
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/*
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* With x2apic, architectural x2apic MSRs are equivalent to the
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* respective synthetic MSRs, so there's no need to override
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* the apic accessors. The only exception is
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* hv_apic_eoi_write, because it benefits from lazy EOI when
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* available, but it works for both xapic and x2apic modes.
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*/
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apic_set_eoi_write(hv_apic_eoi_write);
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apic->read = hv_apic_read;
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apic->write = hv_apic_write;
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apic->icr_write = hv_apic_icr_write;
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apic->icr_read = hv_apic_icr_read;
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if (!x2apic_enabled()) {
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apic->read = hv_apic_read;
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apic->write = hv_apic_write;
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apic->icr_write = hv_apic_icr_write;
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apic->icr_read = hv_apic_icr_read;
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}
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}
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}
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