KVM: x86/mmu: Optimize and clean up so called "last nonleaf level" logic

Drop the pre-computed last_nonleaf_level, which is arguably wrong and at
best confusing.  Per the comment:

  Can have large pages at levels 2..last_nonleaf_level-1.

the intent of the variable would appear to be to track what levels can
_legally_ have large pages, but that intent doesn't align with reality.
The computed value will be wrong for 5-level paging, or if 1gb pages are
not supported.

The flawed code is not a problem in practice, because except for 32-bit
PSE paging, bit 7 is reserved if large pages aren't supported at the
level.  Take advantage of this invariant and simply omit the level magic
math for 64-bit page tables (including PAE).

For 32-bit paging (non-PAE), the adjustments are needed purely because
bit 7 is ignored if PSE=0.  Retain that logic as is, but make
is_last_gpte() unique per PTTYPE so that the PSE check is avoided for
PAE and EPT paging.  In the spirit of avoiding branches, bump the "last
nonleaf level" for 32-bit PSE paging by adding the PSE bit itself.

Note, bit 7 is ignored or has other meaning in CR3/EPTP, but despite
FNAME(walk_addr_generic) briefly grabbing CR3/EPTP in "pte", they are
not PTEs and will blow up all the other gpte helpers.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210622175739.3610207-51-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 0 insertions, 3 deletions

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index f033ecf43d4c..3cd496c8acb8 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -457,9 +457,6 @@ struct kvm_mmu {
 
 	struct rsvd_bits_validate guest_rsvd_check;
 
-	/* Can have large pages at levels 2..last_nonleaf_level-1. */
-	u8 last_nonleaf_level;
-
 	u64 pdptrs[4]; /* pae */
 };