x86/sev-es: Do not unroll string I/O for SEV-ES guests

Under the GHCB specification, SEV-ES guests can support string I/O.
The current #VC handler contains this support, so remove the need to
unroll kernel string I/O operations. This will reduce the number of #VC
exceptions generated as well as the number VM exits for the guest.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/3de04b5b638546ac75d42ba52307fe1a922173d3.1612203987.git.thomas.lendacky@amd.com

arch/x86/mm/mem_encrypt.c

@@ -474,9 +474,10 @@ void __init mem_encrypt_init(void)
 	swiotlb_update_mem_attributes();
 
 	/*
-	 * With SEV, we need to unroll the rep string I/O instructions.
+	 * With SEV, we need to unroll the rep string I/O instructions,
+	 * but SEV-ES supports them through the #VC handler.
 	 */
-	if (sev_active())
+	if (sev_active() && !sev_es_active())
 		static_branch_enable(&sev_enable_key);
 
 	print_mem_encrypt_feature_info();