[Xen-devel] Re: [PATCH] avoid gp fault vmexits

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 6 May 2006, at 03:01, Kamble, Nitin A wrote:

> Hi Keir, Ian,
>     The current Xen code for VMX is setting the gp fault vmexiting in 
> the EXCEPTION_BITMAP vmcs control. There is no need for that as VMM is 
> just plainly re-injecting back to the guest. The attached is a simple 
> patch to set the vmcs control properly.
>  
This is a nice way round the 'int 0xff' vm86 problem. With this patch 
in place, might we be better to crash the guest if we see a valid 
IDT_VECTORING_INFO_FIELD *and* vector_injected? Unlike #GP I can't 
really see how a valid guest is going to end up triggering a 
guest-visible #PG off of an interrupt/exception delivery (and I expect 
#DB/#BP/#NM are all impossible). Also, the current logic will lose 
ExtIRQs which would be a harder problem to track down than an explicit 
domain_crash().
Perhaps, given that this check would get pushed inside the 'rare path' 
of seeing a valid IDT_VECTORING_INFO_FIELD, we could get rid of the 
vector_injected software flag and simply check VM_ENTRY_INTR_INFO_FIELD 
directly? Something like:
__vmread(IDT_VECTORING_INFO_FIELD, &idtv_info_field);
if (idtv_info_field & INTR_INFO_VALID_MASK) {
    __vmread(VM_ENTRY_INTR_INFO_FIELD, &vmentry_intr_info_field);
    if (vmentry_intr_info_field & INTR_INFO_VALID_MASK)
        domain_crash_synchronous(); /* guest fault occurred during 
event injection */
    ....

 -- Keir


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