[Xen-devel] [Patch] Add VMX memory-mapped Local APIC access optimization

["Cui, Dexuan" <dexuan.cui@xxxxxxxxx>]

Some operating systems access the local APIC TPR very frequently, and we
handle that using software-based local APIC virtualization in Xen today.
Such virtualization incurs a number of VM exits from the memory-access
instructions against the APIC page in the guest. 

The attached patch enables the TPR shadow feature that provides APIC TPR
virtualization in hardware. Our tests indicate it can significantly
boost the performance of such guests including 32-bit Windows XP/2003. 

Moreover, with the patch, local APIC accesses other than TPR in guests
are intercepted directly as APIC_ACCESS VM exits rather than PAGE_FAULT
VM exits; this can lower the emulation cost of such accesses.

Signed-off-by: Dexuan Cui <dexuan.cui@xxxxxxxxx>

PS, the related document is available in the latest Intel SDM 3B:
http://www.intel.com/products/processor/manuals/index.htm

Attachment: vTPR-J3.patch
Description: vTPR-J3.patch

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