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Re: [Xen-devel] [PATCH 2/2] x86/svm: Add checks for nested HW features

On 21/12/17 15:26, Brian Woods wrote:
> Add a nestedhvm_enable() check to the existing checks for setting the
> virtual GIF and virtual VMLOAD/VMSAVE features.  If it isn't a nestedhvm
> guest, do not enable the features in the VMCB.
> Signed-off-by: Brian Woods <brian.woods@xxxxxxx>

Unfortunately, nestedhvm_enabled() is guaranteed to be false at the
point that construct_vmcb() is called (due the order in which
information appears while constructing the VM), which means we will
never enable these optimisations.

Combined with the observation of EFER in the pipeline, the logic to
enable/disable these optimisations needs to be in
svm_update_guest_efer(), and need to trigger when EFER.SVME changes.


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