x86: centralize setting SWIOTLB_FORCE when guest memory encryption is enabled

Move enabling SWIOTLB_FORCE for guest memory encryption into common code.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Tested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

arch/x86/kernel/cpu/mshyperv.c

@@ -337,14 +337,6 @@ static void __init ms_hyperv_init_platform(void)
 			swiotlb_unencrypted_base = ms_hyperv.shared_gpa_boundary;
 #endif
 		}
-
-#ifdef CONFIG_SWIOTLB
-		/*
-		 * Enable swiotlb force mode in Isolation VM to
-		 * use swiotlb bounce buffer for dma transaction.
-		 */
-		swiotlb_force = SWIOTLB_FORCE;
-#endif
 		/* Isolation VMs are unenlightened SEV-based VMs, thus this check: */
 		if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT)) {
 			if (hv_get_isolation_type() != HV_ISOLATION_TYPE_NONE)

arch/x86/kernel/pci-dma.c

@@ -53,6 +53,14 @@ static void __init pci_swiotlb_detect(void)
 	if (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT))
 		x86_swiotlb_enable = true;
 
+	/*
+	 * Guest with guest memory encryption currently perform all DMA through
+	 * bounce buffers as the hypervisor can't access arbitrary VM memory
+	 * that is not explicitly shared with it.
+	 */
+	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
+		swiotlb_force = SWIOTLB_FORCE;
+
 	if (swiotlb_force == SWIOTLB_FORCE)
 		x86_swiotlb_enable = true;
 }

arch/x86/mm/mem_encrypt_amd.c

@@ -432,9 +432,6 @@ void __init sme_early_init(void)
 	for (i = 0; i < ARRAY_SIZE(protection_map); i++)
 		protection_map[i] = pgprot_encrypted(protection_map[i]);
 
-	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
-		swiotlb_force = SWIOTLB_FORCE;
-
 	x86_platform.guest.enc_status_change_prepare = amd_enc_status_change_prepare;
 	x86_platform.guest.enc_status_change_finish  = amd_enc_status_change_finish;
 	x86_platform.guest.enc_tlb_flush_required    = amd_enc_tlb_flush_required;