KVM: VMX: Use flag to indicate "active" uret MSRs instead of sorting list

Explicitly flag a uret MSR as needing to be loaded into hardware instead of
resorting the list of "active" MSRs and tracking how many MSRs in total
need to be loaded.  The only benefit to sorting the list is that the loop
to load MSRs during vmx_prepare_switch_to_guest() doesn't need to iterate
over all supported uret MRS, only those that are active.  But that is a
pointless optimization, as the most common case, running a 64-bit guest,
will load the vast majority of MSRs.  Not to mention that a single WRMSR is
far more expensive than iterating over the list.

Providing a stable list order obviates the need to track a given MSR's
"slot" in the per-CPU list of user return MSRs; all lists simply use the
same ordering.  Future patches will take advantage of the stable order to
further simplify the related code.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210504171734.1434054-10-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index d71ed8b425c5..16e4e457ba23 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -36,7 +36,7 @@ struct vmx_msrs {
 };
 
 struct vmx_uret_msr {
-	unsigned int slot; /* The MSR's slot in kvm_user_return_msrs. */
+	bool load_into_hardware;
 	u64 data;
 	u64 mask;
 };