From: Dexuan Cui <decui@microsoft.com> mainline inclusion from mainline-v5.11-rc1 commit d981059e13ffa9ed03a73472e932d070323bd057 category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/IC9GHN Reference: https://github.com/torvalds/linux/commit/d981059e13ffa9ed03a73472e932d070323... -------------------------------- When a Linux VM runs on Hyper-V, if the VM has CPUs with >255 APIC IDs, the CPUs can't be the destination of IOAPIC interrupts, because the IOAPIC RTE's Dest Field has only 8 bits. Currently the hackery driver drivers/iommu/hyperv-iommu.c is used to ensure IOAPIC interrupts are only routed to CPUs that don't have >255 APIC IDs. However, there is an issue with kdump, because the kdump kernel can run on any CPU, and hence IOAPIC interrupts can't work if the kdump kernel run on a CPU with a >255 APIC ID. The kdump issue can be fixed by the Extended Dest ID, which is introduced recently by David Woodhouse (for IOAPIC, see the field virt_destid_8_14 in struct IO_APIC_route_entry). Of course, the Extended Dest ID needs the support of the underlying hypervisor. The latest Hyper-V has added the support recently: with this commit, on such a Hyper-V host, Linux VM does not use hyperv-iommu.c because hyperv_prepare_irq_remapping() returns -ENODEV; instead, Linux kernel's generic support of Extended Dest ID from David is used, meaning that Linux VM is able to support up to 32K CPUs, and IOAPIC interrupts can be routed to all the CPUs. On an old Hyper-V host that doesn't support the Extended Dest ID, nothing changes with this commit: Linux VM is still able to bring up the CPUs with
255 APIC IDs with the help of hyperv-iommu.c, but IOAPIC interrupts still can not go to such CPUs, and the kdump kernel still can not work properly on such CPUs.
[ tglx: Updated comment as suggested by David ] Signed-off-by: Dexuan Cui <decui@microsoft.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: David Woodhouse <dwmw@amazon.co.uk> Link: https://lore.kernel.org/r/20201103011136.59108-1-decui@microsoft.com Signed-off-by: Liu Chao <liuchao173@huawei.com> --- arch/x86/include/asm/hyperv-tlfs.h | 7 +++++++ arch/x86/kernel/cpu/mshyperv.c | 29 +++++++++++++++++++++++++++++ 2 files changed, 36 insertions(+) diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h index 0ed20e8bba9e..6bf42aed387e 100644 --- a/arch/x86/include/asm/hyperv-tlfs.h +++ b/arch/x86/include/asm/hyperv-tlfs.h @@ -23,6 +23,13 @@ #define HYPERV_CPUID_IMPLEMENT_LIMITS 0x40000005 #define HYPERV_CPUID_NESTED_FEATURES 0x4000000A +#define HYPERV_CPUID_VIRT_STACK_INTERFACE 0x40000081 +#define HYPERV_VS_INTERFACE_EAX_SIGNATURE 0x31235356 /* "VS#1" */ + +#define HYPERV_CPUID_VIRT_STACK_PROPERTIES 0x40000082 +/* Support for the extended IOAPIC RTE format */ +#define HYPERV_VS_PROPERTIES_EAX_EXTENDED_IOAPIC_RTE BIT(2) + #define HYPERV_HYPERVISOR_PRESENT_BIT 0x80000000 #define HYPERV_CPUID_MIN 0x40000005 #define HYPERV_CPUID_MAX 0x4000ffff diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c index 05ef1f4550cb..f628e3dc150f 100644 --- a/arch/x86/kernel/cpu/mshyperv.c +++ b/arch/x86/kernel/cpu/mshyperv.c @@ -366,9 +366,38 @@ static void __init ms_hyperv_init_platform(void) mark_tsc_unstable("running on Hyper-V"); } +static bool __init ms_hyperv_x2apic_available(void) +{ + return x2apic_supported(); +} + +/* + * If ms_hyperv_msi_ext_dest_id() returns true, hyperv_prepare_irq_remapping() + * returns -ENODEV and the Hyper-V IOMMU driver is not used; instead, the + * generic support of the 15-bit APIC ID is used: see __irq_msi_compose_msg(). + * + * Note: for a VM on Hyper-V, the I/O-APIC is the only device which + * (logically) generates MSIs directly to the system APIC irq domain. + * There is no HPET, and PCI MSI/MSI-X interrupts are remapped by the + * pci-hyperv host bridge. + */ +static bool __init ms_hyperv_msi_ext_dest_id(void) +{ + u32 eax; + + eax = cpuid_eax(HYPERV_CPUID_VIRT_STACK_INTERFACE); + if (eax != HYPERV_VS_INTERFACE_EAX_SIGNATURE) + return false; + + eax = cpuid_eax(HYPERV_CPUID_VIRT_STACK_PROPERTIES); + return eax & HYPERV_VS_PROPERTIES_EAX_EXTENDED_IOAPIC_RTE; +} + const __initconst struct hypervisor_x86 x86_hyper_ms_hyperv = { .name = "Microsoft Hyper-V", .detect = ms_hyperv_platform, .type = X86_HYPER_MS_HYPERV, + .init.x2apic_available = ms_hyperv_x2apic_available, + .init.msi_ext_dest_id = ms_hyperv_msi_ext_dest_id, .init.init_platform = ms_hyperv_init_platform, }; -- 2.33.0