Re: [Xen-devel] [PATCH RFC 5/9] xen: Support for VMCALL mem_events

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.07.14 at 17:54, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>>> --- a/xen/arch/x86/hvm/vmx/vmx.c
>>> +++ b/xen/arch/x86/hvm/vmx/vmx.c
>>> @@ -2880,8 +2880,21 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
>>>      case EXIT_REASON_VMCALL:
>>>      {
>>>          int rc;
>>> +        unsigned long eax = regs->eax;
>>> +
>>>          HVMTRACE_1D(VMMCALL, regs->eax);
>>> -        rc = hvm_do_hypercall(regs);
>>> +
>>> +        if ( regs->eax != 0x494e5452 ) /* Introcore magic */
>> 
>> Urgh?!
> 
> The magic constant is INTR, and it's used to differentiate between
> "regular" and induced VMCALLs. Our application sets EAX up like that to
> tell the situations apart.

But that needs (a) a #define and (b) an explanation.

Plus - what keeps code outside of your app to invoke this?

>>> --- a/xen/include/public/hvm/params.h
>>> +++ b/xen/include/public/hvm/params.h
>>> @@ -148,6 +148,8 @@
>>>  #define HVM_PARAM_IOREQ_SERVER_PFN 32
>>>  #define HVM_PARAM_NR_IOREQ_SERVER_PAGES 33
>>>  
>>> -#define HVM_NR_PARAMS          34
>>> +#define HVM_PARAM_MEMORY_EVENT_VMCALL 34
>> 
>> So why does this (used only as an argument to
>> hvm_memory_event_traps()) need to be settable? I guess the patch
>> description is just too brief.
> 
> Settable?

You must have a reason to make this a HVM param. That reason is
what I'm asking for.

Jan


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