KVM: x86: Add an emulation flag for implicit system access

Upstream commit: 3963c52df42231f72277cd138994ac94f1183d2b
Conflict: none

Add an emulation flag X86EMUL_F_IMPLICIT to identify implicit system access
in instruction emulation.  Don't bother wiring up any usage at this point,
as Linear Address Space Separation (LASS) will be the first "real" consumer
of the flag and LASS support will require dedicated hooks, i.e. there
aren't any existing calls where passing X86EMUL_F_IMPLICIT is meaningful.

Add the IMPLICIT flag even though there's no imminent usage so that
Linear Address Masking (LAM) support can reference the flag to document
that addresses for implicit accesses aren't untagged.

Intel-SIG: commit 3963c52df422 KVM: x86: Add an emulation flag for
implicit system access
Backport KVM Linear Address Masking (LAM) support.

Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
Tested-by: Xuelian Guo <xuelian.guo@intel.com>
Link: https://lore.kernel.org/r/20230913124227.12574-4-binbin.wu@linux.intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
[ Zhiquan Li: amend commit log ]
Signed-off-by: Zhiquan Li <zhiquan1.li@intel.com>

arch/x86/kvm/kvm_emulate.h

@@ -91,6 +91,7 @@ struct x86_instruction_info {
 /* x86-specific emulation flags */
 #define X86EMUL_F_WRITE			BIT(0)
 #define X86EMUL_F_FETCH			BIT(1)
+#define X86EMUL_F_IMPLICIT		BIT(2)
 
 struct x86_emulate_ops {
 	void (*vm_bugged)(struct x86_emulate_ctxt *ctxt);