Re: [Xen-devel] [PATCH v3 1/2] x86/hvm/viridian: keep APIC assist page mapped...

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Paul Durrant [mailto:paul.durrant@xxxxxxxxxx]
> Sent: 16 March 2016 17:44
> To: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Paul Durrant; Keir (Xen.org); Jan Beulich; Andrew Cooper
> Subject: [PATCH v3 1/2] x86/hvm/viridian: keep APIC assist page mapped...
> 
> ... for the lifetime of the domain.
> 
> If Xen is to make use of the APIC assist enlightenment then a persistent
> mapping needs to be kept, rather than the temporary one which is currently
> used only to initialize the page content.
> 
> This patch also adds a comment block at the top of the source with
> information on the latest version of the spec. from Microsoft and the
> current URL where it may be found.
> 
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> Cc: Keir Fraser <keir@xxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> 
> v2:
>  - Re-instated warning if the initialization of an APIC assist page fails.
>  - Added up-to-date information about the viridian specification to the
>    comment block at the top of the source.
> ---
>  xen/arch/x86/hvm/hvm.c             |  2 +
>  xen/arch/x86/hvm/viridian.c        | 76 ++++++++++++++++++++++++++++---
> -------
>  xen/include/asm-x86/hvm/viridian.h |  8 +++-
>  3 files changed, 65 insertions(+), 21 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index 4ea51d7..f446ee4 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -2606,6 +2606,8 @@ int hvm_vcpu_initialise(struct vcpu *v)
> 
>  void hvm_vcpu_destroy(struct vcpu *v)
>  {
> +    viridian_vcpu_deinit(v);
> +
>      hvm_all_ioreq_servers_remove_vcpu(v->domain, v);
> 
>      if ( hvm_altp2m_supported() )
> diff --git a/xen/arch/x86/hvm/viridian.c b/xen/arch/x86/hvm/viridian.c
> index 1ee22aa..e990163 100644
> --- a/xen/arch/x86/hvm/viridian.c
> +++ b/xen/arch/x86/hvm/viridian.c
> @@ -1,7 +1,12 @@
> 
> /**********************************************************
> ********************
>   * viridian.c
>   *
> - * An implementation of the Viridian hypercall interface.
> + * An implementation of some Viridian enlightenments. See Microsoft's
> + * Hypervisor Top Level Functional Specification (v4.0b) at:
> + *
> + * https://msdn.microsoft.com/en-
> us/virtualization/hyperv_on_windows/develop/tlfs
> + *
> + * for more information.
>   */
> 
>  #include <xen/sched.h>
> @@ -163,7 +168,7 @@ static void dump_apic_assist(const struct vcpu *v)
>  {
>      const union viridian_apic_assist *aa;
> 
> -    aa = &v->arch.hvm_vcpu.viridian.apic_assist;
> +    aa = &v->arch.hvm_vcpu.viridian.apic_assist.msr;
> 
>      printk(XENLOG_G_INFO "%pv: VIRIDIAN APIC_ASSIST: enabled: %x pfn:
> %lx\n",
>             v, aa->fields.enabled, (unsigned long)aa->fields.pfn);
> @@ -217,9 +222,9 @@ static void enable_hypercall_page(struct domain *d)
>  static void initialize_apic_assist(struct vcpu *v)
>  {
>      struct domain *d = v->domain;
> -    unsigned long gmfn = v->arch.hvm_vcpu.viridian.apic_assist.fields.pfn;
> +    unsigned long gmfn = v-
> >arch.hvm_vcpu.viridian.apic_assist.msr.fields.pfn;
>      struct page_info *page = get_page_from_gfn(d, gmfn, NULL,
> P2M_ALLOC);
> -    uint8_t *p;
> +    void *va;
> 
>      /*
>       * We don't yet make use of the APIC assist page but by setting
> @@ -227,25 +232,49 @@ static void initialize_apic_assist(struct vcpu *v)
>       * bound to support the MSR. We therefore do just enough to keep
> windows
>       * happy.
>       *
> -     * See http://msdn.microsoft.com/en-
> us/library/ff538657%28VS.85%29.aspx for
> -     * details of how Windows uses the page.
> +     * See section 13.3.4.1 of the specification for details of this
> +     * enlightenment.
>       */
> 
> -    if ( !page || !get_page_type(page, PGT_writable_page) )
> +    if ( !page )
> +        goto fail;
> +
> +    if ( !get_page_type(page, PGT_writable_page) )
>      {
> -        if ( page )
> -            put_page(page);
> -        gdprintk(XENLOG_WARNING, "Bad GMFN %lx (MFN %lx)\n", gmfn,
> -                 page ? page_to_mfn(page) : INVALID_MFN);
> -        return;
> +        put_page(page);
> +        goto fail;
>      }
> 
> -    p = __map_domain_page(page);
> +    va = __map_domain_page_global(page);
> +    if ( !va )
> +    {
> +        put_page_and_type(page);
> +        goto fail;
> +    }
> 
> -    *(u32 *)p = 0;
> +    *(uint32_t *)va = 0;
> 
> -    unmap_domain_page(p);
> +    v->arch.hvm_vcpu.viridian.apic_assist.page = page;
> +    v->arch.hvm_vcpu.viridian.apic_assist.va = va;
> +    return;
> +
> + fail:
> +    gdprintk(XENLOG_WARNING, "Bad GMFN %lx (MFN %lx)\n", gmfn,
> +             page ? page_to_mfn(page) : INVALID_MFN);
> +}
> +
> +static void teardown_apic_assist(struct vcpu *v)
> +{
> +    struct page_info *page = v->arch.hvm_vcpu.viridian.apic_assist.page;
> +    void *va = v->arch.hvm_vcpu.viridian.apic_assist.va;
> 
> +    if ( !va )
> +        return;
> +
> +    v->arch.hvm_vcpu.viridian.apic_assist.va = NULL;
> +    v->arch.hvm_vcpu.viridian.apic_assist.page = NULL;
> +
> +    unmap_domain_page_global(va);
>      put_page_and_type(page);
>  }
> 
> @@ -374,9 +403,9 @@ int wrmsr_viridian_regs(uint32_t idx, uint64_t val)
> 
>      case VIRIDIAN_MSR_APIC_ASSIST:
>          perfc_incr(mshv_wrmsr_apic_msr);
> -        v->arch.hvm_vcpu.viridian.apic_assist.raw = val;
> +        v->arch.hvm_vcpu.viridian.apic_assist.msr.raw = val;
>          dump_apic_assist(v);
> -        if (v->arch.hvm_vcpu.viridian.apic_assist.fields.enabled)
> +        if ( v->arch.hvm_vcpu.viridian.apic_assist.msr.fields.enabled )

Actually there's an omission here. If the MSR had previously been set then we 
potentially leak a mapping so there needs to be a teardown before the 
(re-)initialize.

  Paul

>              initialize_apic_assist(v);
>          break;
> 
> @@ -485,7 +514,7 @@ int rdmsr_viridian_regs(uint32_t idx, uint64_t *val)
> 
>      case VIRIDIAN_MSR_APIC_ASSIST:
>          perfc_incr(mshv_rdmsr_apic_msr);
> -        *val = v->arch.hvm_vcpu.viridian.apic_assist.raw;
> +        *val = v->arch.hvm_vcpu.viridian.apic_assist.msr.raw;
>          break;
> 
>      case VIRIDIAN_MSR_REFERENCE_TSC:
> @@ -521,6 +550,11 @@ int rdmsr_viridian_regs(uint32_t idx, uint64_t *val)
>      return 1;
>  }
> 
> +void viridian_vcpu_deinit(struct vcpu *v)
> +{
> +    teardown_apic_assist(v);
> +}
> +
>  static DEFINE_PER_CPU(cpumask_t, ipi_cpumask);
> 
>  int viridian_hypercall(struct cpu_user_regs *regs)
> @@ -721,7 +755,7 @@ static int viridian_save_vcpu_ctxt(struct domain *d,
> hvm_domain_context_t *h)
>      for_each_vcpu( d, v ) {
>          struct hvm_viridian_vcpu_context ctxt;
> 
> -        ctxt.apic_assist = v->arch.hvm_vcpu.viridian.apic_assist.raw;
> +        ctxt.apic_assist = v->arch.hvm_vcpu.viridian.apic_assist.msr.raw;
> 
>          if ( hvm_save_entry(VIRIDIAN_VCPU, v->vcpu_id, h, &ctxt) != 0 )
>              return 1;
> @@ -747,7 +781,9 @@ static int viridian_load_vcpu_ctxt(struct domain *d,
> hvm_domain_context_t *h)
>      if ( hvm_load_entry(VIRIDIAN_VCPU, h, &ctxt) != 0 )
>          return -EINVAL;
> 
> -    v->arch.hvm_vcpu.viridian.apic_assist.raw = ctxt.apic_assist;
> +    v->arch.hvm_vcpu.viridian.apic_assist.msr.raw = ctxt.apic_assist;
> +    if ( v->arch.hvm_vcpu.viridian.apic_assist.msr.fields.enabled )
> +        initialize_apic_assist(v);
> 
>      return 0;
>  }
> diff --git a/xen/include/asm-x86/hvm/viridian.h b/xen/include/asm-
> x86/hvm/viridian.h
> index c4319d7..ee3a120 100644
> --- a/xen/include/asm-x86/hvm/viridian.h
> +++ b/xen/include/asm-x86/hvm/viridian.h
> @@ -21,7 +21,11 @@ union viridian_apic_assist
> 
>  struct viridian_vcpu
>  {
> -    union viridian_apic_assist apic_assist;
> +    struct {
> +        union viridian_apic_assist msr;
> +        struct page_info *page;
> +        void *va;
> +    } apic_assist;
>  };
> 
>  union viridian_guest_os_id
> @@ -117,6 +121,8 @@ viridian_hypercall(struct cpu_user_regs *regs);
>  void viridian_time_ref_count_freeze(struct domain *d);
>  void viridian_time_ref_count_thaw(struct domain *d);
> 
> +void viridian_vcpu_deinit(struct vcpu *v);
> +
>  #endif /* __ASM_X86_HVM_VIRIDIAN_H__ */
> 
>  /*
> --
> 2.1.4


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