KVM: x86/mmu: Optimize MMU page cache lookup for all direct SPs

Commit fb58a9c3 ("KVM: x86/mmu: Optimize MMU page cache lookup for
fully direct MMUs") skipped the unsync checks and write flood clearing
for full direct MMUs. We can extend this further to skip the checks for
all direct shadow pages. Direct shadow pages in indirect MMUs (i.e.
shadow paging) are used when shadowing a guest huge page with smaller
pages. Such direct shadow pages, like their counterparts in fully direct
MMUs, are never marked unsynced or have a non-zero write-flooding count.

Checking sp->role.direct also generates better code than checking
direct_map because, due to register pressure, direct_map has to get
shoved onto the stack and then pulled back off.

No functional change intended.

Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20220516232138.1783324-2-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>