Re: [Qemu-devel] [PATCH 1/2] kvm/x86: Hyper-V based guest crash data handling

[Paolo Bonzini]

On 11/06/2015 15:18, Denis V. Lunev wrote:
> From: Andrey Smetanin <address@hidden>
> 
> Windows 2012 guests can notify hypervisor about occurred guest crash
> (Windows bugcheck(BSOD)) by writing specific Hyper-V msrs. This patch does
> handling of this MSR's by KVM and sending notification to user space that
> allows to gather Windows guest crash dump by QEMU/LIBVIRT.
> 
> The idea is to provide functionality equal to pvpanic device without
> QEMU guest agent for Windows.
> 
> The idea is borrowed from Linux HyperV bus driver and validated against
> Windows 2k12.
> 
> Signed-off-by: Andrey Smetanin <address@hidden>
> Signed-off-by: Denis V. Lunev <address@hidden>
> CC: Gleb Natapov <address@hidden>
> CC: Paolo Bonzini <address@hidden>
> ---
>  arch/x86/include/uapi/asm/hyperv.h | 10 +++++
>  arch/x86/kvm/Makefile              |  2 +-
>  arch/x86/kvm/mshv.c                | 84 
> ++++++++++++++++++++++++++++++++++++++
>  arch/x86/kvm/mshv.h                | 32 +++++++++++++++

Please use hyperv.[ch] or hyper-v.[ch] and name the functions kvm_hv_*.
 We can later move more functions from x86.c to the new file, so it's
better to keep the names consistent.

>  arch/x86/kvm/x86.c                 | 25 ++++++++++++
>  include/linux/kvm_host.h           | 17 ++++++++
>  include/uapi/linux/kvm.h           | 11 +++++
>  7 files changed, 180 insertions(+), 1 deletion(-)
>  create mode 100644 arch/x86/kvm/mshv.c
>  create mode 100644 arch/x86/kvm/mshv.h
> 
> diff --git a/arch/x86/include/uapi/asm/hyperv.h 
> b/arch/x86/include/uapi/asm/hyperv.h
> index ce6068d..25f3064 100644
> --- a/arch/x86/include/uapi/asm/hyperv.h
> +++ b/arch/x86/include/uapi/asm/hyperv.h
> @@ -199,6 +199,16 @@
>  #define HV_X64_MSR_STIMER3_CONFIG            0x400000B6
>  #define HV_X64_MSR_STIMER3_COUNT             0x400000B7
>  
> +
> +/* Hypev-V guest crash notification MSR's */
> +#define HV_X64_MSR_CRASH_P0                  0x40000100
> +#define HV_X64_MSR_CRASH_P1                  0x40000101
> +#define HV_X64_MSR_CRASH_P2                  0x40000102
> +#define HV_X64_MSR_CRASH_P3                  0x40000103
> +#define HV_X64_MSR_CRASH_P4                  0x40000104
> +#define HV_X64_MSR_CRASH_CTL                 0x40000105
> +#define HV_CRASH_CTL_CRASH_NOTIFY            (1ULL << 63)
> +
>  #define HV_X64_MSR_HYPERCALL_ENABLE          0x00000001
>  #define HV_X64_MSR_HYPERCALL_PAGE_ADDRESS_SHIFT      12
>  #define HV_X64_MSR_HYPERCALL_PAGE_ADDRESS_MASK       \
> diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
> index 16e8f96..b1ec24d 100644
> --- a/arch/x86/kvm/Makefile
> +++ b/arch/x86/kvm/Makefile
> @@ -12,7 +12,7 @@ kvm-y                       += $(KVM)/kvm_main.o 
> $(KVM)/coalesced_mmio.o \
>  kvm-$(CONFIG_KVM_ASYNC_PF)   += $(KVM)/async_pf.o
>  
>  kvm-y                        += x86.o mmu.o emulate.o i8259.o irq.o lapic.o \
> -                        i8254.o ioapic.o irq_comm.o cpuid.o pmu.o
> +                        i8254.o ioapic.o irq_comm.o cpuid.o pmu.o mshv.o
>  kvm-$(CONFIG_KVM_DEVICE_ASSIGNMENT)  += assigned-dev.o iommu.o
>  kvm-intel-y          += vmx.o
>  kvm-amd-y            += svm.o
> diff --git a/arch/x86/kvm/mshv.c b/arch/x86/kvm/mshv.c
> new file mode 100644
> index 0000000..ad367c44
> --- /dev/null
> +++ b/arch/x86/kvm/mshv.c
> @@ -0,0 +1,84 @@
> +/*
> + * KVM Microsoft Hyper-V extended paravirtualization
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2.  See
> + * the COPYING file in the top-level directory.
> + *
> + * Copyright (C) 2015 Andrey Smetanin <address@hidden>
> + *
> + * Authors: Andrey Smetanin address@hidden
> + */
> +
> +#include <linux/kvm_host.h>
> +#include "mshv.h"
> +
> +int kvm_mshv_ctx_create(struct kvm *kvm)
> +{
> +     struct kvm_mshv_ctx *ctx;
> +
> +     ctx = kzalloc(sizeof(struct kvm_mshv_ctx), GFP_KERNEL);
> +     if (!ctx)
> +             return -ENOMEM;
> +
> +     ctx->kvm = kvm;
> +     atomic_set(&ctx->crash_pending, 0);
> +     kvm->mshv_ctx = ctx;
> +     return 0;
> +}
> +
> +void kvm_mshv_ctx_destroy(struct kvm *kvm)
> +{
> +     kfree(kvm->mshv_ctx);
> +}
> +
> +int kvm_mshv_msr_get_crash_ctl(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
> +{
> +     struct kvm_mshv_ctx *ctx = kvm_vcpu_get_mshv_ctx(vcpu);
> +
> +     atomic_set(&ctx->crash_pending, 1);
> +
> +     /* Response that KVM ready to receive crash data */
> +     *pdata = HV_CRASH_CTL_CRASH_NOTIFY;
> +     return 0;
> +}
> +
> +int kvm_mshv_msr_set_crash_ctl(struct kvm_vcpu *vcpu, u32 msr, u64 data)
> +{
> +     struct kvm_mshv_ctx *ctx = kvm_vcpu_get_mshv_ctx(vcpu);
> +
> +     if (atomic_dec_and_test(&ctx->crash_pending)) {
> +             pr_debug("vcpu %p 0x%llx 0x%llx 0x%llx 0x%llx 0x%llx",
> +                      vcpu, ctx->crash_p0, ctx->crash_p1, ctx->crash_p2,
> +                      ctx->crash_p3, ctx->crash_p4);
> +
> +             /* Crash data almost gathered so notify user space */

Why "almost" gathered?

> +             kvm_make_request(KVM_REQ_MSHV_CRASH, vcpu);
> +     }
> +
> +     return 0;
> +}
> +
> +int kvm_mshv_msr_set_crash_data(struct kvm_vcpu *vcpu, u32 msr, u64 data)
> +{
> +     struct kvm_mshv_ctx *ctx = kvm_vcpu_get_mshv_ctx(vcpu);
> +
> +     switch (msr) {
> +     case HV_X64_MSR_CRASH_P0:
> +             ctx->crash_p0 = data;
> +             return 0;
> +     case HV_X64_MSR_CRASH_P1:
> +             ctx->crash_p1 = data;
> +             return 0;
> +     case HV_X64_MSR_CRASH_P2:
> +             ctx->crash_p2 = data;
> +             return 0;
> +     case HV_X64_MSR_CRASH_P3:
> +             ctx->crash_p3 = data;
> +             return 0;
> +     case HV_X64_MSR_CRASH_P4:
> +             ctx->crash_p4 = data;
> +             return 0;

Please use an array (with a WARN_ON_ONCE check that the index is in bounds).

> +     default:
> +             return -EINVAL;
> +     }
> +}
> diff --git a/arch/x86/kvm/mshv.h b/arch/x86/kvm/mshv.h
> new file mode 100644
> index 0000000..ce8e7fa
> --- /dev/null
> +++ b/arch/x86/kvm/mshv.h
> @@ -0,0 +1,32 @@
> +/*
> + * KVM Microsoft Hyper-V extended paravirtualization
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2.  See
> + * the COPYING file in the top-level directory.
> + *
> + * Copyright (C) 2015 Andrey Smetanin <address@hidden>
> + *
> + * Authors: Andrey Smetanin address@hidden
> + */
> +
> +#ifndef __ARCH_X86_KVM_MSHV_H__
> +#define __ARCH_X86_KVM_MSHV_H__
> +
> +static inline struct kvm_mshv_ctx *kvm_get_mshv_ctx(struct kvm *vm)
> +{
> +     return vm->mshv_ctx;
> +}
> +
> +static inline struct kvm_mshv_ctx *kvm_vcpu_get_mshv_ctx(struct kvm_vcpu 
> *vcpu)
> +{
> +     return vcpu->kvm->mshv_ctx;
> +}
> +
> +int kvm_mshv_msr_get_crash_ctl(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata);
> +int kvm_mshv_msr_set_crash_ctl(struct kvm_vcpu *vcpu, u32 msr, u64 data);
> +int kvm_mshv_msr_set_crash_data(struct kvm_vcpu *vcpu, u32 msr, u64 data);
> +
> +int kvm_mshv_ctx_create(struct kvm *kvm);
> +void kvm_mshv_ctx_destroy(struct kvm *kvm);
> +
> +#endif
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index ea306ad..388b58f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -28,6 +28,7 @@
>  #include "x86.h"
>  #include "cpuid.h"
>  #include "assigned-dev.h"
> +#include "mshv.h"
>  
>  #include <linux/clocksource.h>
>  #include <linux/interrupt.h>
> @@ -2338,6 +2339,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct 
> msr_data *msr_info)
>               } else
>                       return set_msr_hyperv(vcpu, msr, data);
>               break;
> +     case HV_X64_MSR_CRASH_CTL:
> +             return kvm_mshv_msr_set_crash_ctl(vcpu, msr, data);
> +     case HV_X64_MSR_CRASH_P0 ... HV_X64_MSR_CRASH_P4:
> +             return kvm_mshv_msr_set_crash_data(vcpu, msr, data);
>       case MSR_IA32_BBL_CR_CTL3:
>               /* Drop writes to this legacy MSR -- see rdmsr
>                * counterpart for further detail.
> @@ -2650,6 +2655,8 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, 
> u64 *pdata)
>               } else
>                       return get_msr_hyperv(vcpu, msr, pdata);
>               break;
> +     case HV_X64_MSR_CRASH_CTL:
> +             return kvm_mshv_msr_get_crash_ctl(vcpu, msr, pdata);

Please implement get_crash_data as well.  Userspace may want to retrieve
this value and stash it somewhere for post-mortem analysis, and
KVM_GET_MSR is very handy for this purpose.

Do not return an error, just return the last written datum.

>       case MSR_IA32_BBL_CR_CTL3:
>               /* This legacy MSR exists but isn't fully documented in current
>                * silicon.  It is however accessed by winxp in very narrow
> @@ -6280,6 +6287,20 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>                       vcpu_scan_ioapic(vcpu);
>               if (kvm_check_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu))
>                       kvm_vcpu_reload_apic_access_page(vcpu);
> +             if (kvm_check_request(KVM_REQ_MSHV_CRASH, vcpu)) {
> +                     struct kvm_mshv_ctx *ctx = kvm_vcpu_get_mshv_ctx(vcpu);
> +
> +                     vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT;
> +                     vcpu->run->system_event.type = KVM_SYSTEM_EVENT_CRASH;
> +                     vcpu->run->system_event.flags = 0;
> +                     vcpu->run->system_event.crash.p0 = ctx->crash_p0;
> +                     vcpu->run->system_event.crash.p1 = ctx->crash_p1;
> +                     vcpu->run->system_event.crash.p2 = ctx->crash_p2;
> +                     vcpu->run->system_event.crash.p3 = ctx->crash_p3;
> +                     vcpu->run->system_event.crash.p4 = ctx->crash_p4;
> +                     r = 0;
> +                     goto out;
> +             }
>       }
>  
>       if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {
> @@ -7418,6 +7439,9 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long 
> type)
>       if (type)
>               return -EINVAL;
>  
> +     if (kvm_mshv_ctx_create(kvm))
> +             return -ENOMEM;
> +
>       INIT_HLIST_HEAD(&kvm->arch.mask_notifier_list);
>       INIT_LIST_HEAD(&kvm->arch.active_mmu_pages);
>       INIT_LIST_HEAD(&kvm->arch.zapped_obsolete_pages);
> @@ -7484,6 +7508,7 @@ void kvm_arch_sync_events(struct kvm *kvm)
>  
>  void kvm_arch_destroy_vm(struct kvm *kvm)
>  {
> +     kvm_mshv_ctx_destroy(kvm);
>       if (current->mm == kvm->mm) {
>               /*
>                * Free memory regions allocated on behalf of userspace,
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index ad45054..83bd7bf 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -134,6 +134,7 @@ static inline bool is_error_page(struct page *page)
>  #define KVM_REQ_ENABLE_IBS        23
>  #define KVM_REQ_DISABLE_IBS       24
>  #define KVM_REQ_APIC_PAGE_RELOAD  25
> +#define KVM_REQ_MSHV_CRASH        26
>  
>  #define KVM_USERSPACE_IRQ_SOURCE_ID          0
>  #define KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID     1
> @@ -343,6 +344,21 @@ struct kvm_memslots {
>       int used_slots;
>  };
>  
> +/*
> + * Ms hyperv paravirt context
> + */
> +struct kvm_mshv_ctx {

This should be in an x86-specific file.  Please name it "struct
kvm_arch_hyperv hv" and stick it inside struct kvm_arch (so it's
accessed as kvm->arch.hv).  We can also move other fields, e.g.
kvm->arch.hv_hypercall inside this new struct.

> +     struct kvm      *kvm;

Not needed if you avoid the pointer: then you can just use container_of.

> +     atomic_t        crash_pending;
> +
> +     /* Guest crash related parameters */
> +     u64             crash_p0;
> +     u64             crash_p1;
> +     u64             crash_p2;
> +     u64             crash_p3;
> +     u64             crash_p4;
> +};
> +
>  struct kvm {
>       spinlock_t mmu_lock;
>       struct mutex slots_lock;
> @@ -395,6 +411,7 @@ struct kvm {
>  #endif
>       long tlbs_dirty;
>       struct list_head devices;
> +     struct kvm_mshv_ctx *mshv_ctx;
>  };
>  
>  #define kvm_err(fmt, ...) \
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 4b60056..12f481b 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -317,8 +317,19 @@ struct kvm_run {
>               struct {
>  #define KVM_SYSTEM_EVENT_SHUTDOWN       1
>  #define KVM_SYSTEM_EVENT_RESET          2
> +#define KVM_SYSTEM_EVENT_CRASH          3
>                       __u32 type;
>                       __u64 flags;
> +                     union {
> +                             struct {
> +                                     /* Guest crash related parameters */
> +                                     __u64 p0;
> +                                     __u64 p1;
> +                                     __u64 p2;
> +                                     __u64 p3;
> +                                     __u64 p4;
> +                             } crash;

No need to return the parameters here.  Userspace can use KVM_GET_MSR to
read them.

Paolo

> +                     };
>               } system_event;
>               /* KVM_EXIT_S390_STSI */
>               struct {
>