Re: [Xen-devel] [PATCH v2 05/12] VMX/altp2m: add code to support EPTP switching and #VE.

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 22/06/15 19:56, Ed White wrote:
> Implement and hook up the code to enable VMX support of VMFUNC and #VE.
>
> VMFUNC leaf 0 (EPTP switching) emulation is added in a later patch.
>
> Signed-off-by: Ed White <edmund.h.white@xxxxxxxxx>
> ---
>  xen/arch/x86/hvm/vmx/vmx.c | 132 
> +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 132 insertions(+)
>
> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> index 2d3ad63..e8d9c82 100644
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -56,6 +56,7 @@
>  #include <asm/debugger.h>
>  #include <asm/apic.h>
>  #include <asm/hvm/nestedhvm.h>
> +#include <asm/hvm/altp2mhvm.h>
>  #include <asm/event.h>
>  #include <asm/monitor.h>
>  #include <public/arch-x86/cpuid.h>
> @@ -1763,6 +1764,100 @@ static void vmx_enable_msr_exit_interception(struct 
> domain *d)
>                                           MSR_TYPE_W);
>  }
>  
> +static void vmx_vcpu_update_eptp(struct vcpu *v)
> +{
> +    struct domain *d = v->domain;
> +    struct p2m_domain *p2m = NULL;
> +    struct ept_data *ept;
> +
> +    if ( altp2mhvm_active(d) )
> +        p2m = p2m_get_altp2m(v);
> +    if ( !p2m )
> +        p2m = p2m_get_hostp2m(d);
> +
> +    ept = &p2m->ept;
> +    ept->asr = pagetable_get_pfn(p2m_get_pagetable(p2m));
> +
> +    vmx_vmcs_enter(v);
> +
> +    __vmwrite(EPT_POINTER, ept_get_eptp(ept));
> +
> +    if ( v->arch.hvm_vmx.secondary_exec_control &
> +        SECONDARY_EXEC_ENABLE_VIRT_EXCEPTIONS )
> +        __vmwrite(EPTP_INDEX, vcpu_altp2mhvm(v).p2midx);
> +
> +    vmx_vmcs_exit(v);
> +}
> +
> +static void vmx_vcpu_update_vmfunc_ve(struct vcpu *v)
> +{
> +    struct domain *d = v->domain;
> +    u32 mask = SECONDARY_EXEC_ENABLE_VM_FUNCTIONS;
> +
> +    if ( !cpu_has_vmx_vmfunc )
> +        return;
> +
> +    if ( cpu_has_vmx_virt_exceptions )
> +        mask |= SECONDARY_EXEC_ENABLE_VIRT_EXCEPTIONS;
> +
> +    vmx_vmcs_enter(v);
> +
> +    if ( !d->is_dying && altp2mhvm_active(d) )
> +    {
> +        v->arch.hvm_vmx.secondary_exec_control |= mask;
> +        __vmwrite(VM_FUNCTION_CONTROL, VMX_VMFUNC_EPTP_SWITCHING);
> +        __vmwrite(EPTP_LIST_ADDR, virt_to_maddr(d->arch.altp2m_eptp));
> +
> +        if ( cpu_has_vmx_virt_exceptions )
> +        {
> +            p2m_type_t t;
> +            mfn_t mfn;
> +
> +            mfn = get_gfn_query_unlocked(d, vcpu_altp2mhvm(v).veinfo_gfn, 
> &t);

get_gfn_query_unlocked() returns _mfn(INVALID_MFN) in the failure case,
which you must not blindly write back.

> +            __vmwrite(VIRT_EXCEPTION_INFO, mfn_x(mfn) << PAGE_SHIFT);

pfn_to_paddr() please, rather than opencoding it.  (This is a helper
which needs cleaning up, name-wise).

> +        }
> +    }
> +    else
> +        v->arch.hvm_vmx.secondary_exec_control &= ~mask;
> +
> +    __vmwrite(SECONDARY_VM_EXEC_CONTROL,
> +        v->arch.hvm_vmx.secondary_exec_control);
> +
> +    vmx_vmcs_exit(v);
> +}
> +
> +static bool_t vmx_vcpu_emulate_ve(struct vcpu *v)
> +{
> +    bool_t rc = 0;
> +    ve_info_t *veinfo = vcpu_altp2mhvm(v).veinfo_gfn ?
> +        hvm_map_guest_frame_rw(vcpu_altp2mhvm(v).veinfo_gfn, 0) : NULL;

gfn 0 is a valid (albeit unlikely) location to request the veinfo page. 
Use GFN_INVALID as the sentinel.

> +
> +    if ( !veinfo )
> +        return 0;
> +
> +    if ( veinfo->semaphore != 0 )
> +        goto out;

The semantics of this semaphore are not clearly spelled out in the
manual.  The only information I can locate concerning this field is in
note in 25.5.6.1 which says:

"Delivery of virtualization exceptions writes the value FFFFFFFFH to
offset 4 in the virtualization-exception informa-
tion area (see Section 25.5.6.2). Thus, once a virtualization exception
occurs, another can occur only if software
clears this field."

I presume this should be taken to mean "software writes 0 to this
field", but some clarification would be nice.

> +
> +    rc = 1;
> +
> +    veinfo->exit_reason = EXIT_REASON_EPT_VIOLATION;
> +    veinfo->semaphore = ~0l;

semaphore is declared as an unsigned field, so should use ~0u.

> +    veinfo->eptp_index = vcpu_altp2mhvm(v).p2midx;
> +
> +    vmx_vmcs_enter(v);
> +    __vmread(EXIT_QUALIFICATION, &veinfo->exit_qualification);
> +    __vmread(GUEST_LINEAR_ADDRESS, &veinfo->gla);
> +    __vmread(GUEST_PHYSICAL_ADDRESS, &veinfo->gpa);
> +    vmx_vmcs_exit(v);
> +
> +    hvm_inject_hw_exception(TRAP_virtualisation,
> +                            HVM_DELIVER_NO_ERROR_CODE);
> +
> +out:
> +    hvm_unmap_guest_frame(veinfo, 0);
> +    return rc;
> +}
> +
>  static struct hvm_function_table __initdata vmx_function_table = {
>      .name                 = "VMX",
>      .cpu_up_prepare       = vmx_cpu_up_prepare,
> @@ -1822,6 +1917,9 @@ static struct hvm_function_table __initdata 
> vmx_function_table = {
>      .nhvm_hap_walk_L1_p2m = nvmx_hap_walk_L1_p2m,
>      .hypervisor_cpuid_leaf = vmx_hypervisor_cpuid_leaf,
>      .enable_msr_exit_interception = vmx_enable_msr_exit_interception,
> +    .ahvm_vcpu_update_eptp = vmx_vcpu_update_eptp,
> +    .ahvm_vcpu_update_vmfunc_ve = vmx_vcpu_update_vmfunc_ve,
> +    .ahvm_vcpu_emulate_ve = vmx_vcpu_emulate_ve,
>  };
>  
>  const struct hvm_function_table * __init start_vmx(void)
> @@ -2754,6 +2852,40 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
>  
>      /* Now enable interrupts so it's safe to take locks. */
>      local_irq_enable();
> + 
> +    /*
> +     * If the guest has the ability to switch EPTP without an exit,
> +     * figure out whether it has done so and update the altp2m data.
> +     */
> +    if ( altp2mhvm_active(v->domain) &&
> +        (v->arch.hvm_vmx.secondary_exec_control &
> +        SECONDARY_EXEC_ENABLE_VM_FUNCTIONS) )
> +    {
> +        unsigned long idx;
> +
> +        if ( v->arch.hvm_vmx.secondary_exec_control &
> +            SECONDARY_EXEC_ENABLE_VIRT_EXCEPTIONS )
> +            __vmread(EPTP_INDEX, &idx);
> +        else
> +        {
> +            unsigned long eptp;
> +
> +            __vmread(EPT_POINTER, &eptp);
> +
> +            if ( !p2m_find_altp2m_by_eptp(v->domain, eptp, &idx) )
> +            {
> +                gdprintk(XENLOG_ERR, "EPTP not found in alternate p2m 
> list\n");
> +                domain_crash(v->domain);
> +            }
> +        }
> +

Is it worth checking that idx is plausible at this point, before blindly
writing it back into the vcpu structure?

~Andrew

> +        if ( (uint16_t)idx != vcpu_altp2mhvm(v).p2midx )
> +        {
> +            atomic_dec(&p2m_get_altp2m(v)->active_vcpus);
> +            vcpu_altp2mhvm(v).p2midx = (uint16_t)idx;
> +            atomic_inc(&p2m_get_altp2m(v)->active_vcpus);
> +        }
> +    }
>  
>      /* XXX: This looks ugly, but we need a mechanism to ensure
>       * any pending vmresume has really happened


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