KVM: x86: Drop .post_leave_smm(), i.e. the manual post-RSM MMU reset

Drop the .post_leave_smm() emulator callback, which at this point is just
a wrapper to kvm_mmu_reset_context().  The manual context reset is
unnecessary, because unlike enter_smm() which calls vendor MSR/CR helpers
directly, em_rsm() bounces through the KVM helpers, e.g. kvm_set_cr4(),
which are responsible for processing side effects.  em_rsm() is already
subtly relying on this behavior as it doesn't manually do
kvm_update_cpuid_runtime(), e.g. to recognize CR4.OSXSAVE changes.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210609185619.992058-9-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/emulate.c

@@ -2591,8 +2591,14 @@ static int em_rsm(struct x86_emulate_ctxt *ctxt)
 	if (ret != X86EMUL_CONTINUE)
 		goto emulate_shutdown;
 
-	ctxt->ops->post_leave_smm(ctxt);
-
+	/*
+	 * Note, the ctxt->ops callbacks are responsible for handling side
+	 * effects when writing MSRs and CRs, e.g. MMU context resets, CPUID
+	 * runtime updates, etc...  If that changes, e.g. this flow is moved
+	 * out of the emulator to make it look more like enter_smm(), then
+	 * those side effects need to be explicitly handled for both success
+	 * and shutdown.
+	 */
 	return X86EMUL_CONTINUE;
 
 emulate_shutdown:

arch/x86/kvm/kvm_emulate.h

@@ -233,7 +233,6 @@ struct x86_emulate_ops {
 	void (*exiting_smm)(struct x86_emulate_ctxt *ctxt);
 	int (*pre_leave_smm)(struct x86_emulate_ctxt *ctxt,
 			     const char *smstate);
-	void (*post_leave_smm)(struct x86_emulate_ctxt *ctxt);
 	void (*triple_fault)(struct x86_emulate_ctxt *ctxt);
 	int (*set_xcr)(struct x86_emulate_ctxt *ctxt, u32 index, u64 xcr);
 };

arch/x86/kvm/x86.c

@@ -7222,11 +7222,6 @@ static int emulator_pre_leave_smm(struct x86_emulate_ctxt *ctxt,
 	return static_call(kvm_x86_pre_leave_smm)(emul_to_vcpu(ctxt), smstate);
 }
 
-static void emulator_post_leave_smm(struct x86_emulate_ctxt *ctxt)
-{
-	kvm_mmu_reset_context(emul_to_vcpu(ctxt));
-}
-
 static void emulator_triple_fault(struct x86_emulate_ctxt *ctxt)
 {
 	kvm_make_request(KVM_REQ_TRIPLE_FAULT, emul_to_vcpu(ctxt));
@@ -7280,7 +7275,6 @@ static const struct x86_emulate_ops emulate_ops = {
 	.get_hflags          = emulator_get_hflags,
 	.exiting_smm         = emulator_exiting_smm,
 	.pre_leave_smm       = emulator_pre_leave_smm,
-	.post_leave_smm      = emulator_post_leave_smm,
 	.triple_fault        = emulator_triple_fault,
 	.set_xcr             = emulator_set_xcr,
 };