Question When VM-Exited

[mutiancheng]

When VM-Exit occured and it hasn't vmresumed, if Thread Dispatching is activiated what should happen?

1. Can threads on none-root CPU be dispatched to the VM-Exited CPU?
   2.On VM-Exited CPU, shouldn't the current thread be dispatched to other non-root CPUs?

[tandasat]

While VM-exit is being processed, any interruptions should not be allowed, as the processor is on the more privileged code and we do not want it to run arbitrary kernel code. So 2 is correct (actually, should not be dispatched to anyone else)

[mutiancheng]

When VM-exit occurs, if IF=1 and IRQL<DISPATCH_LEVEL, how can you ensure that the current CPU will not to be dispatched to run another thread?

[tandasat]

A host's (VMM's) flag register is loaded from VMCS and not affected by guest's status.Also, the IF flag is always cleared for the host if I recall correctly (I was not able to find the statement in the SDM, so could be wrong). If interrupts are disabled, a thread is not dispatched as timer interrupt does not occur. Best, Satoshi

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On Fri, Mar 3, 2017 at 5:49 PM, mutiancheng ***@***.***> wrote: When VM-exit occurs, if IF=1 and IRQL<DISPATCH_LEVEL, how can you ensure that the current CPU will not to be dispatched to run another thread? — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#11 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABi7u8TrEgI0UZJdvR9baKVtSKfauj0sks5riAU4gaJpZM4MRxE9> .

[tandasat]

Sorry, I gave you an wrong answer. As "Loading Host RIP, RSP, and RFLAGS"
states, RFLAGS is cleared, except bit 1, which is always set. So the TF flag is always zero, unless you manually enable it.

[mutiancheng]

Yes, I observed it with WinDbg. Thank you for your patience and attentiveness. Is the statement in the SDM? I will read it.

[tandasat]

No problem :) and yes, that is in the SDM.