Re: [Xen-devel] [PATCH v3 1/3] Nested VMX: Check VMX capability before read VMX related MSRs.

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

Andrew Cooper wrote on 2013-09-11:
> On 11/09/13 03:52, Yang Zhang wrote:
>> From: Yang Zhang <yang.z.zhang@xxxxxxxxx>
>> 
>> VMX MSRs only available when the CPU support the VMX feature. In addition,
>> VMX_TRUE* MSRs only available when bit 55 of VMX_BASIC MSR is set.
>> 
>> Signed-off-by: Yang Zhang <yang.z.zhang@xxxxxxxxx>
>> ---
>>  xen/arch/x86/hvm/vmx/vmcs.c |    3 ++-
>>  xen/arch/x86/hvm/vmx/vvmx.c |   22 ++++++++++++++++++++++
>>  2 files changed, 24 insertions(+), 1 deletions(-)
>> diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
>> index 31347bb..f8d2a9d 100644
>> --- a/xen/arch/x86/hvm/vmx/vmcs.c
>> +++ b/xen/arch/x86/hvm/vmx/vmcs.c
>> @@ -78,6 +78,7 @@ static DEFINE_PER_CPU(struct list_head,
> active_vmcs_list);
>>  static DEFINE_PER_CPU(bool_t, vmxon);
>>  
>>  static u32 vmcs_revision_id __read_mostly;
>> +u32 vmx_basic_msr_low, vmx_basic_msr_high;
>> 
>>  static void __init vmx_display_features(void)
>>  {
>> @@ -133,7 +134,7 @@ static bool_t cap_check(const char *name, u32
>> expected, u32 saw)
>> 
>>  static int vmx_init_vmcs_config(void)
>>  {
>> -    u32 vmx_basic_msr_low, vmx_basic_msr_high, min, opt;
>> +    u32 min, opt;
>>      u32 _vmx_pin_based_exec_control;
>>      u32 _vmx_cpu_based_exec_control;
>>      u32 _vmx_secondary_exec_control = 0;
>> diff --git a/xen/arch/x86/hvm/vmx/vvmx.c b/xen/arch/x86/hvm/vmx/vvmx.c
>> index cecc72f..554d5c0 100644
>> --- a/xen/arch/x86/hvm/vmx/vvmx.c
>> +++ b/xen/arch/x86/hvm/vmx/vvmx.c
>> @@ -31,6 +31,7 @@
>>  static DEFINE_PER_CPU(u64 *, vvmcs_buf);
>>  
>>  static void nvmx_purge_vvmcs(struct vcpu *v);
>> +extern u32 vmx_basic_msr_high;
>> 
>>  #define VMCS_BUF_SIZE 100
>> @@ -1814,12 +1815,33 @@ int nvmx_handle_invvpid(struct cpu_user_regs
> *regs)
>>  int nvmx_msr_read_intercept(unsigned int msr, u64 *msr_content)
>>  {
>>      struct vcpu *v = current; +    unsigned int eax, ebx, ecx, edx;
>>      u64 data = 0, host_data = 0; int r = 1;
>>      
>>      if ( !nestedhvm_enabled(v->domain) )
>>          return 0;
>> +    /* VMX capablity MSRs are available only when guest supports VMX. */
>> +    hvm_cpuid(0x1, &eax, &ebx, &ecx, &edx);
>> +    if ( !(ecx & cpufeat_mask(X86_FEATURE_VMXE)) )
>> +        return 0;
>> +
>> +    /*
>> +     * Those MSRs are available only when bit 55 of
>> +     * MSR_IA32_VMX_BASIC is set.
>> +     */
>> +    switch (msr) {
>> +    case MSR_IA32_VMX_TRUE_PINBASED_CTLS:
>> +    case MSR_IA32_VMX_TRUE_PROCBASED_CTLS:
>> +    case MSR_IA32_VMX_TRUE_EXIT_CTLS:
>> +    case MSR_IA32_VMX_TRUE_ENTRY_CTLS:
>> +        if ( !(vmx_basic_msr_high & VMX_BASIC_DEFAULT1_ZERO >> 32) )
>> +            return 0;
>> +    default:
>> +        break;
> 
> default:
>     break;
> Is completely useless here.

Yes. I added them here to let the code look like much neatly. Compiler will 
ignore them.


Best regards,
Yang



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