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KVM: x86/mmu: Micro-optimize nEPT's bad memptype/XWR checks
Rework the handling of nEPT's bad memtype/XWR checks to micro-optimize the checks as much as possible. Move the check to a separate helper, __is_bad_mt_xwr(), which allows the guest_rsvd_check usage in paging_tmpl.h to omit the check entirely for paging32/64 (bad_mt_xwr is always zero for non-nEPT) while retaining the bitwise-OR of the current code for the shadow_zero_check in walk_shadow_page_get_mmio_spte(). Add a comment for the bitwise-OR usage in the mmio spte walk to avoid future attempts to "fix" the code, which is what prompted this optimization in the first place[*]. Opportunistically remove the superfluous '!= 0' and parantheses, and use BIT_ULL() instead of open coding its equivalent. The net effect is that code generation is largely unchanged for walk_shadow_page_get_mmio_spte(), marginally better for ept_prefetch_invalid_gpte(), and significantly improved for paging32/64_prefetch_invalid_gpte(). Note, walk_shadow_page_get_mmio_spte() can't use a templated version of the memtype/XRW as it works on the host's shadow PTEs, e.g. checks that KVM hasn't borked its EPT tables. Even if it could be templated, the benefits of having a single implementation far outweight the few uops that would be saved for NPT or non-TDP paging, e.g. most compilers inline it all the way to up kvm_mmu_page_fault(). [*] https://lkml.kernel.org/r/20200108001859.25254-1-sean.j.christopherson@intel.com Cc: Jim Mattson <jmattson@google.com> Cc: David Laight <David.Laight@ACULAB.COM> Cc: Arvind Sankar <nivedita@alum.mit.edu> Signed-off-by:Sean Christopherson <sean.j.christopherson@intel.com> Reviewed-by: