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authorAvi Kivity <avi@redhat.com>2012-09-12 14:52:00 +0300
committerAvi Kivity <avi@redhat.com>2012-09-20 13:00:08 +0300
commit97d64b788114be1c4dc4bfe7a8ba2bf9643fe6af (patch)
tree50dfed391cb52aba63cc41d0cdbdf07ee2d792e4 /arch/x86/pci/Makefile
parent8cbc70696f149e44753b0fe60162b4ff96c2dd2b (diff)
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KVM: MMU: Optimize pte permission checks
walk_addr_generic() permission checks are a maze of branchy code, which is performed four times per lookup. It depends on the type of access, efer.nxe, cr0.wp, cr4.smep, and in the near future, cr4.smap. Optimize this away by precalculating all variants and storing them in a bitmap. The bitmap is recalculated when rarely-changing variables change (cr0, cr4) and is indexed by the often-changing variables (page fault error code, pte access permissions). The permission check is moved to the end of the loop, otherwise an SMEP fault could be reported as a false positive, when PDE.U=1 but PTE.U=0. Noted by Xiao Guangrong. The result is short, branch-free code. Reviewed-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> Signed-off-by: Avi Kivity <avi@redhat.com>
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