Re: [PATCH v2 2/2] vm_event: consolidate hvm_event_fill_regs and p2m_vm_event_fill_regs

[Razvan Cojocaru <rcojocaru@bitdefender.com>]

On 02/12/2016 11:57 AM, Jan Beulich wrote:
>>>> On 12.02.16 at 01:22, <tlengyel@novetta.com> wrote:
>> --- a/xen/arch/x86/vm_event.c
>> +++ b/xen/arch/x86/vm_event.c
>> @@ -122,6 +122,65 @@ void vm_event_set_registers(struct vcpu *v, vm_event_response_t *rsp)
>>      v->arch.user_regs.eip = rsp->data.regs.x86.rip;
>>  }
>>  
>> +void vm_event_fill_regs(vm_event_request_t *req)
>> +{
>> +    const struct cpu_user_regs *regs = guest_cpu_user_regs();
>> +    struct segment_register seg;
>> +    struct hvm_hw_cpu ctxt;
>> +    struct vcpu *curr = current;
>> +
>> +    req->data.regs.x86.rax = regs->eax;
>> +    req->data.regs.x86.rcx = regs->ecx;
>> +    req->data.regs.x86.rdx = regs->edx;
>> +    req->data.regs.x86.rbx = regs->ebx;
>> +    req->data.regs.x86.rsp = regs->esp;
>> +    req->data.regs.x86.rbp = regs->ebp;
>> +    req->data.regs.x86.rsi = regs->esi;
>> +    req->data.regs.x86.rdi = regs->edi;
>> +
>> +    req->data.regs.x86.r8  = regs->r8;
>> +    req->data.regs.x86.r9  = regs->r9;
>> +    req->data.regs.x86.r10 = regs->r10;
>> +    req->data.regs.x86.r11 = regs->r11;
>> +    req->data.regs.x86.r12 = regs->r12;
>> +    req->data.regs.x86.r13 = regs->r13;
>> +    req->data.regs.x86.r14 = regs->r14;
>> +    req->data.regs.x86.r15 = regs->r15;
>> +
>> +    req->data.regs.x86.rflags = regs->eflags;
>> +    req->data.regs.x86.rip    = regs->eip;
>> +
>> +    if ( !is_hvm_domain(curr->domain) )
>> +        return;
> 
> No such check existed in either of the two original functions. Why is
> it needed all of the sudden? And if it is needed, why do the other
> fields not get filled (as far as possible at least) for PV guests?

I can't speak for Tamas, but I suspect the check has been placed there
because calls to hvm_funcs.save_cpu_ctxt(curr, &ctxt) and
hvm_get_segment_register(curr, x86_seg_fs, &seg) follow, and he's put
vm_event_fill_regs() in xen/arch/x86/vm_event.c (a previous function was
called hvm_event_fill_regs(), in arch/x86/hvm/event.c, so no checking
for HVM was needed).

I don't think the check is needed for the current codepaths, but since
the code has been moved to xen/arch/x86/ the question about future PV
events is fair.


Thanks,
Razvan