x86/hyper-v: Add hyperv Isolation VM check in the cc_platform_has()

Hyper-V provides Isolation VM for confidential computing support and
guest memory is encrypted in it. Places checking cc_platform_has()
with GUEST_MEM_ENCRYPT attr should return "True" in Isolation VM.

Hyper-V Isolation VMs need to adjust the SWIOTLB size just like SEV
guests. Add a hyperv_cc_platform_has() variant which enables that.
Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
Acked-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20211213071407.314309-3-ltykernel@gmail.comSigned-off-by: Wei Liu <wei.liu@kernel.org>

arch/x86/kernel/cc_platform.c

@@ -11,6 +11,7 @@
 #include <linux/cc_platform.h>
 #include <linux/mem_encrypt.h>
 
+#include <asm/mshyperv.h>
 #include <asm/processor.h>
 
 static bool __maybe_unused intel_cc_platform_has(enum cc_attr attr)
@@ -58,12 +59,19 @@ static bool amd_cc_platform_has(enum cc_attr attr)
 #endif
 }
 
+static bool hyperv_cc_platform_has(enum cc_attr attr)
+{
+	return attr == CC_ATTR_GUEST_MEM_ENCRYPT;
+}
 
 bool cc_platform_has(enum cc_attr attr)
 {
 	if (sme_me_mask)
 		return amd_cc_platform_has(attr);
 
+	if (hv_is_isolation_supported())
+		return hyperv_cc_platform_has(attr);
+
 	return false;
 }
 EXPORT_SYMBOL_GPL(cc_platform_has);