Re: (xen 4.6 unstable) triple fault when execute fxsave during the procedure of guest iso install

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 24/06/15 10:25, Razvan Cojocaru wrote:
> On 06/24/2015 12:14 PM, Fanhenglong wrote:
>> I want to debug the procedure of windows os install with windbg,
>>
>> windbg executes instruction(fxsave) after the blank vm is started and
>> before guest iso start to install,
>>
>> fxsave trigger the following code path:
>> vmx_vmexit_handler(EXIT_REASON_EPT_VIOLATION)
>> ->ept_handle_violation
>> ->hvm_hap_nested_page_fault
>> ->handle_mmio_with_translation
>> ->handle_mmio
>> ->hvm_emulate_one
>> ->x86_emulate
>>
>> *X86_emulate return X86EMUL_UNHANDLEABLE*
> How are you using Xen in this case? Are you by any chance using the
> vm_event system in a way that sends back an "emulate" vm_event response
> from userspace?
>
> You might want to look at x86_emulate() in
> xen/arch/x86/x86_emulate/x86_emulate.c and see if (and how) fxsave is
> being handled.

The fxsave instruction has no emulation implementation.

"0f ae 07" is "fxsave (%rdi)" which means that either introspection is
active, or %rdi is a pointer into an MMIO region.

~Andrew