Re: [RFC PATCH v5 21/52] i386/xen: handle VCPUOP_register_vcpu_info

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* David Woodhouse (dwmw2@infradead.org) wrote:
> From: Joao Martins <joao.m.martins@oracle.com>
> 
> Handle the hypercall to set a per vcpu info, and also wire up the default
> vcpu_info in the shared_info page for the first 32 vCPUs.
> 
> To avoid deadlock within KVM a vCPU thread must set its *own* vcpu_info
> rather than it being set from the context in which the hypercall is
> invoked.
> 
> Add the vcpu_info (and default) GPA to the vmstate_x86_cpu for migration,
> and restore it in kvm_arch_put_registers() appropriately.
> 
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> ---
>  target/i386/cpu.h            |   2 +
>  target/i386/kvm/kvm.c        |  17 ++++
>  target/i386/kvm/trace-events |   1 +
>  target/i386/kvm/xen-emu.c    | 152 ++++++++++++++++++++++++++++++++++-
>  target/i386/kvm/xen-emu.h    |   2 +
>  target/i386/machine.c        |  19 +++++
>  6 files changed, 190 insertions(+), 3 deletions(-)
> 
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index c6c57baed5..109b2e5669 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -1788,6 +1788,8 @@ typedef struct CPUArchState {
>  #endif
>  #if defined(CONFIG_KVM)
>      struct kvm_nested_state *nested_state;
> +    uint64_t xen_vcpu_info_gpa;
> +    uint64_t xen_vcpu_info_default_gpa;
>  #endif
>  #if defined(CONFIG_HVF)
>      HVFX86LazyFlags hvf_lflags;
> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> index f365e56fcc..52d69e87e7 100644
> --- a/target/i386/kvm/kvm.c
> +++ b/target/i386/kvm/kvm.c
> @@ -4734,6 +4734,15 @@ int kvm_arch_put_registers(CPUState *cpu, int level)
>          kvm_arch_set_tsc_khz(cpu);
>      }
>  
> +#ifdef CONFIG_XEN_EMU
> +    if (xen_mode == XEN_EMULATE && level == KVM_PUT_FULL_STATE) {
> +        ret = kvm_put_xen_state(cpu);
> +        if (ret < 0) {
> +            return ret;
> +        }
> +    }
> +#endif
> +
>      ret = kvm_getput_regs(x86_cpu, 1);
>      if (ret < 0) {
>          return ret;
> @@ -4833,6 +4842,14 @@ int kvm_arch_get_registers(CPUState *cs)
>      if (ret < 0) {
>          goto out;
>      }
> +#ifdef CONFIG_XEN_EMU
> +    if (xen_mode == XEN_EMULATE) {
> +        ret = kvm_get_xen_state(cs);
> +        if (ret < 0) {
> +            goto out;
> +        }
> +    }
> +#endif
>      ret = 0;
>   out:
>      cpu_sync_bndcs_hflags(&cpu->env);
> diff --git a/target/i386/kvm/trace-events b/target/i386/kvm/trace-events
> index 0a47c26e80..14e54dfca5 100644
> --- a/target/i386/kvm/trace-events
> +++ b/target/i386/kvm/trace-events
> @@ -9,3 +9,4 @@ kvm_x86_update_msi_routes(int num) "Updated %d MSI routes"
>  # xen-emu.c
>  kvm_xen_hypercall(int cpu, uint8_t cpl, uint64_t input, uint64_t a0, uint64_t a1, uint64_t a2, uint64_t ret) "xen_hypercall: cpu %d cpl %d input %" PRIu64 " a0 0x%" PRIx64 " a1 0x%" PRIx64 " a2 0x%" PRIx64" ret 0x%" PRIx64
>  kvm_xen_set_shared_info(uint64_t gfn) "shared info at gfn 0x%" PRIx64
> +kvm_xen_set_vcpu_attr(int cpu, int type, uint64_t gpa) "vcpu attr cpu %d type %d gpa 0x%" PRIx64
> diff --git a/target/i386/kvm/xen-emu.c b/target/i386/kvm/xen-emu.c
> index 0e9ae481d8..aa06588c07 100644
> --- a/target/i386/kvm/xen-emu.c
> +++ b/target/i386/kvm/xen-emu.c
> @@ -120,6 +120,8 @@ int kvm_xen_init(KVMState *s, uint32_t hypercall_msr)
>  
>  int kvm_xen_init_vcpu(CPUState *cs)
>  {
> +    X86CPU *cpu = X86_CPU(cs);
> +    CPUX86State *env = &cpu->env;
>      int err;
>  
>      /*
> @@ -143,6 +145,9 @@ int kvm_xen_init_vcpu(CPUState *cs)
>          }
>      }
>  
> +    env->xen_vcpu_info_gpa = INVALID_GPA;
> +    env->xen_vcpu_info_default_gpa = INVALID_GPA;
> +
>      return 0;
>  }
>  
> @@ -188,10 +193,58 @@ static bool kvm_xen_hcall_xen_version(struct kvm_xen_exit *exit, X86CPU *cpu,
>      return true;
>  }
>  
> +static int kvm_xen_set_vcpu_attr(CPUState *cs, uint16_t type, uint64_t gpa)
> +{
> +    struct kvm_xen_vcpu_attr xhsi;
> +
> +    xhsi.type = type;
> +    xhsi.u.gpa = gpa;
> +
> +    trace_kvm_xen_set_vcpu_attr(cs->cpu_index, type, gpa);
> +
> +    return kvm_vcpu_ioctl(cs, KVM_XEN_VCPU_SET_ATTR, &xhsi);
> +}
> +
> +static void do_set_vcpu_info_default_gpa(CPUState *cs, run_on_cpu_data data)
> +{
> +    X86CPU *cpu = X86_CPU(cs);
> +    CPUX86State *env = &cpu->env;
> +
> +    env->xen_vcpu_info_default_gpa = data.host_ulong;
> +
> +    /* Changing the default does nothing if a vcpu_info was explicitly set. */
> +    if (env->xen_vcpu_info_gpa == INVALID_GPA) {
> +        kvm_xen_set_vcpu_attr(cs, KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO,
> +                              env->xen_vcpu_info_default_gpa);
> +    }
> +}
> +
> +static void do_set_vcpu_info_gpa(CPUState *cs, run_on_cpu_data data)
> +{
> +    X86CPU *cpu = X86_CPU(cs);
> +    CPUX86State *env = &cpu->env;
> +
> +    env->xen_vcpu_info_gpa = data.host_ulong;
> +
> +    kvm_xen_set_vcpu_attr(cs, KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO,
> +                          env->xen_vcpu_info_gpa);
> +}
> +
> +static void do_vcpu_soft_reset(CPUState *cs, run_on_cpu_data data)
> +{
> +    X86CPU *cpu = X86_CPU(cs);
> +    CPUX86State *env = &cpu->env;
> +
> +    env->xen_vcpu_info_gpa = INVALID_GPA;
> +    env->xen_vcpu_info_default_gpa = INVALID_GPA;
> +
> +    kvm_xen_set_vcpu_attr(cs, KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO, INVALID_GPA);
> +}
> +
>  static int xen_set_shared_info(uint64_t gfn)
>  {
>      uint64_t gpa = gfn << TARGET_PAGE_BITS;
> -    int err;
> +    int i, err;
>  
>      /*
>       * The xen_overlay device tells KVM about it too, since it had to
> @@ -206,6 +259,15 @@ static int xen_set_shared_info(uint64_t gfn)
>  
>      trace_kvm_xen_set_shared_info(gfn);
>  
> +    for (i = 0; i < XEN_LEGACY_MAX_VCPUS; i++) {
> +        CPUState *cpu = qemu_get_cpu(i);
> +        if (cpu) {
> +            async_run_on_cpu(cpu, do_set_vcpu_info_default_gpa,
> +                             RUN_ON_CPU_HOST_ULONG(gpa));
> +        }
> +        gpa += sizeof(vcpu_info_t);
> +    }
> +
>      return err;
>  }
>  
> @@ -363,15 +425,43 @@ static bool kvm_xen_hcall_hvm_op(struct kvm_xen_exit *exit, X86CPU *cpu,
>      }
>  }
>  
> +static int vcpuop_register_vcpu_info(CPUState *cs, CPUState *target,
> +                                     uint64_t arg)
> +{
> +    struct vcpu_register_vcpu_info rvi;
> +    uint64_t gpa;
> +
> +    /* No need for 32/64 compat handling */
> +    qemu_build_assert(sizeof(rvi) == 16);
> +    qemu_build_assert(sizeof(struct vcpu_info) == 64);
> +
> +    if (!target) {
> +        return -ENOENT;
> +    }
> +
> +    if (kvm_copy_from_gva(cs, arg, &rvi, sizeof(rvi))) {
> +        return -EFAULT;
> +    }
> +
> +    if (rvi.offset > TARGET_PAGE_SIZE - sizeof(struct vcpu_info)) {
> +        return -EINVAL;
> +    }
> +
> +    gpa = ((rvi.mfn << TARGET_PAGE_BITS) + rvi.offset);
> +    async_run_on_cpu(target, do_set_vcpu_info_gpa, RUN_ON_CPU_HOST_ULONG(gpa));
> +    return 0;
> +}
> +
>  static bool kvm_xen_hcall_vcpu_op(struct kvm_xen_exit *exit, X86CPU *cpu,
>                                    int cmd, int vcpu_id, uint64_t arg)
>  {
> +    CPUState *dest = qemu_get_cpu(vcpu_id);
> +    CPUState *cs = CPU(cpu);
>      int err;
>  
>      switch (cmd) {
>      case VCPUOP_register_vcpu_info:
> -        /* no vcpu info placement for now */
> -        err = -ENOSYS;
> +        err = vcpuop_register_vcpu_info(cs, dest, arg);
>          break;
>  
>      default:
> @@ -384,8 +474,13 @@ static bool kvm_xen_hcall_vcpu_op(struct kvm_xen_exit *exit, X86CPU *cpu,
>  
>  static int kvm_xen_soft_reset(void)
>  {
> +    CPUState *cpu;
>      int err;
>  
> +    CPU_FOREACH(cpu) {
> +        async_run_on_cpu(cpu, do_vcpu_soft_reset, RUN_ON_CPU_NULL);
> +    }
> +
>      err = xen_overlay_map_shinfo_page(INVALID_GFN);
>      if (err) {
>          return err;
> @@ -531,3 +626,54 @@ int kvm_xen_handle_exit(X86CPU *cpu, struct kvm_xen_exit *exit)
>                              exit->u.hcall.result);
>      return 0;
>  }
> +
> +int kvm_put_xen_state(CPUState *cs)
> +{
> +    X86CPU *cpu = X86_CPU(cs);
> +    CPUX86State *env = &cpu->env;
> +    uint64_t gpa;
> +    int ret;
> +
> +    gpa = env->xen_vcpu_info_gpa;
> +    if (gpa == INVALID_GPA) {
> +        gpa = env->xen_vcpu_info_default_gpa;
> +    }
> +
> +    if (gpa != INVALID_GPA) {
> +        ret = kvm_xen_set_vcpu_attr(cs, KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO, gpa);
> +        if (ret < 0) {
> +            return ret;
> +        }
> +    }
> +
> +    return 0;
> +}
> +
> +int kvm_get_xen_state(CPUState *cs)
> +{
> +    X86CPU *cpu = X86_CPU(cs);
> +    CPUX86State *env = &cpu->env;
> +    uint64_t gpa;
> +
> +    /*
> +     * The kernel does not mark vcpu_info as dirty when it delivers interrupts
> +     * to it. It's up to userspace to *assume* that any page shared thus is
> +     * always considered dirty. The shared_info page is different since it's
> +     * an overlay and migrated separately anyway.
> +     */
> +    gpa = env->xen_vcpu_info_gpa;
> +    if (gpa == INVALID_GPA) {
> +        gpa = env->xen_vcpu_info_default_gpa;
> +    }
> +    if (gpa != INVALID_GPA) {
> +        MemoryRegionSection mrs = memory_region_find(get_system_memory(),
> +                                                     gpa,
> +                                                     sizeof(struct vcpu_info));
> +        if (mrs.mr && mrs.size >= sizeof(struct vcpu_info)) {
> +            memory_region_set_dirty(mrs.mr, mrs.offset_within_region,
> +                                    sizeof(struct vcpu_info));
> +        }
> +    }
> +
> +    return 0;
> +}
> diff --git a/target/i386/kvm/xen-emu.h b/target/i386/kvm/xen-emu.h
> index 21faf6bf38..452605699a 100644
> --- a/target/i386/kvm/xen-emu.h
> +++ b/target/i386/kvm/xen-emu.h
> @@ -26,5 +26,7 @@
>  int kvm_xen_init(KVMState *s, uint32_t hypercall_msr);
>  int kvm_xen_init_vcpu(CPUState *cs);
>  int kvm_xen_handle_exit(X86CPU *cpu, struct kvm_xen_exit *exit);
> +int kvm_put_xen_state(CPUState *cs);
> +int kvm_get_xen_state(CPUState *cs);
>  
>  #endif /* QEMU_I386_KVM_XEN_EMU_H */
> diff --git a/target/i386/machine.c b/target/i386/machine.c
> index 310b125235..1215e616c8 100644
> --- a/target/i386/machine.c
> +++ b/target/i386/machine.c
> @@ -6,8 +6,10 @@
>  #include "kvm/hyperv.h"
>  #include "hw/i386/x86.h"
>  #include "kvm/kvm_i386.h"
> +#include "hw/xen/xen.h"
>  
>  #include "sysemu/kvm.h"
> +#include "sysemu/kvm_xen.h"
>  #include "sysemu/tcg.h"
>  
>  #include "qemu/error-report.h"
> @@ -1257,6 +1259,22 @@ static const VMStateDescription vmstate_nested_state = {
>      }
>  };
>  
> +static bool xen_vcpu_needed(void *opaque)
> +{
> +    return (xen_mode == XEN_EMULATE);
> +}
> +
> +static const VMStateDescription vmstate_xen_vcpu = {
> +    .name = "cpu/xen_vcpu",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .needed = xen_vcpu_needed,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_UINT64(env.xen_vcpu_info_gpa, X86CPU),
> +        VMSTATE_UINT64(env.xen_vcpu_info_default_gpa, X86CPU),
> +        VMSTATE_END_OF_LIST()
> +    }
> +};
>  #endif
>  
>  static bool mcg_ext_ctl_needed(void *opaque)
> @@ -1716,6 +1734,7 @@ const VMStateDescription vmstate_x86_cpu = {
>  #endif
>  #ifdef CONFIG_KVM
>          &vmstate_nested_state,
> +        &vmstate_xen_vcpu,

Yep, that shoudln't break anything as long as xen_vcpu_needed is false,
so yeh, OK from migration.

Dave

>  #endif
>          &vmstate_msr_tsx_ctrl,
>          &vmstate_msr_intel_sgx,
> -- 
> 2.35.3
> 
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK