b5c3c1b3c6
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: Vitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.