Re: [RFC PATCH 4/4] KVM: vmx: add support for emulating UMIP

From: Yang Zhang
Date: Wed Jul 13 2016 - 05:54:41 EST

On 2016/7/13 17:35, Paolo Bonzini wrote:

On 13/07/2016 11:21, Yang Zhang wrote:

+ if ((cr4 & X86_CR4_UMIP) && !boot_cpu_has(X86_FEATURE_UMIP)) {
+ hw_cr4 &= ~X86_CR4_UMIP;
+ } else
+ vmcs_clear_bits(SECONDARY_VM_EXEC_CONTROL,

Since the faults based on privilege level have priority over VM exits.
So we don't need to enable/disable SECONDARY_EXEC_DESC dynamically.
Instead, we can set it unconditionally.

I'm setting it dynamically because it slows down LGDT, LLDT, LIDT and LTR.

You are right. And SGDT, SIDT, SLDT, SMSW, STR also will be intercepted even in CPL 0 if we don't disable it.

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