[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 06/12] VMX: add VMFUNC leaf 0 (EPTP switching) to emulator.
>>> On 24.06.15 at 22:29, <edmund.h.white@xxxxxxxxx> wrote: > On 06/24/2015 05:47 AM, Andrew Cooper wrote: >>> + case EXIT_REASON_VMFUNC: >>> + if ( vmx_vmfunc_intercept(regs) == X86EMUL_OKAY ) >> >> This is currently an unconditional failure, and I don't see subsequent >> patches which alter vmx_vmfunc_intercept(). Shouldn't >> vmx_vmfunc_intercept() switch on eax and optionally call >> p2m_switch_vcpu_altp2m_by_id()? > > If the VMFUNC instruction was valid, the hardware would have executed it. > The only time a VMFUNC exit occurs is if the hardware supports VMFUNC > and the hypervisor has enabled it, but the VMFUNC instruction is > invalid in some way and can't be executed (because EAX != 0, for example). > > There are only two choices: crash the domain or inject #UD (which is the > closest analogue to what happens in the absence of a hypervisor and will > probably crash the OS in the domain). I chose the latter in the code I > originally wrote; Ravi chose the former in his patch. I don't have a > strong opinion either way, but I think these are the only two choices. Injecting an exception should always be preferred, as that gives the guest at least a theoretical chance of recovering. The closer to real hardware, the better. I.e. if hardware without a hypervisor gives #UD here, so should the emulation do. (Still I admit that the case is somewhat fuzzy, as the instruction specifically exists to be used under a hypervisor. But #UD being raised for EAX >= 64 makes it a good candidate for smaller but invalid EAX values too imo.) > I hope this answers Jan's question in another email on the same subject. It does, thanks. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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