drivers: hv: Mark percpu hvcall input arg page unencrypted in SEV-SNP enlightened guest

Hypervisor needs to access input arg, VMBus synic event and
message pages. Mark these pages unencrypted in the SEV-SNP
guest and free them only if they have been marked encrypted
successfully.
Reviewed-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Tianyu Lan <tiala@microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Link: https://lore.kernel.org/r/20230818102919.1318039-5-ltykernel@gmail.com

drivers/hv/hv.c

@@ -20,6 +20,7 @@
 #include <linux/interrupt.h>
 #include <clocksource/hyperv_timer.h>
 #include <asm/mshyperv.h>
+#include <linux/set_memory.h>
 #include "hyperv_vmbus.h"
 
 /* The one and only */
@@ -78,7 +79,7 @@ int hv_post_message(union hv_connection_id connection_id,
 
 int hv_synic_alloc(void)
 {
-	int cpu;
+	int cpu, ret = -ENOMEM;
 	struct hv_per_cpu_context *hv_cpu;
 
 	/*
@@ -123,26 +124,76 @@ int hv_synic_alloc(void)
 				goto err;
 			}
 		}
+
+		if (hv_isolation_type_en_snp()) {
+			ret = set_memory_decrypted((unsigned long)
+				hv_cpu->synic_message_page, 1);
+			if (ret) {
+				pr_err("Failed to decrypt SYNIC msg page: %d\n", ret);
+				hv_cpu->synic_message_page = NULL;
+
+				/*
+				 * Free the event page here so that hv_synic_free()
+				 * won't later try to re-encrypt it.
+				 */
+				free_page((unsigned long)hv_cpu->synic_event_page);
+				hv_cpu->synic_event_page = NULL;
+				goto err;
+			}
+
+			ret = set_memory_decrypted((unsigned long)
+				hv_cpu->synic_event_page, 1);
+			if (ret) {
+				pr_err("Failed to decrypt SYNIC event page: %d\n", ret);
+				hv_cpu->synic_event_page = NULL;
+				goto err;
+			}
+
+			memset(hv_cpu->synic_message_page, 0, PAGE_SIZE);
+			memset(hv_cpu->synic_event_page, 0, PAGE_SIZE);
+		}
 	}
 
 	return 0;
+
 err:
 	/*
 	 * Any memory allocations that succeeded will be freed when
 	 * the caller cleans up by calling hv_synic_free()
 	 */
-	return -ENOMEM;
+	return ret;
 }
 
 
 void hv_synic_free(void)
 {
-	int cpu;
+	int cpu, ret;
 
 	for_each_present_cpu(cpu) {
 		struct hv_per_cpu_context *hv_cpu
 			= per_cpu_ptr(hv_context.cpu_context, cpu);
 
+		/* It's better to leak the page if the encryption fails. */
+		if (hv_isolation_type_en_snp()) {
+			if (hv_cpu->synic_message_page) {
+				ret = set_memory_encrypted((unsigned long)
+					hv_cpu->synic_message_page, 1);
+				if (ret) {
+					pr_err("Failed to encrypt SYNIC msg page: %d\n", ret);
+					hv_cpu->synic_message_page = NULL;
+				}
+			}
+
+			if (hv_cpu->synic_event_page) {
+				ret = set_memory_encrypted((unsigned long)
+					hv_cpu->synic_event_page, 1);
+				if (ret) {
+					pr_err("Failed to encrypt SYNIC event page: %d\n", ret);
+					hv_cpu->synic_event_page = NULL;
+				}
+			}
+		}
+
 		free_page((unsigned long)hv_cpu->synic_event_page);
 		free_page((unsigned long)hv_cpu->synic_message_page);
 	}

drivers/hv/hv_common.c

@@ -24,6 +24,7 @@
 #include <linux/kmsg_dump.h>
 #include <linux/slab.h>
 #include <linux/dma-map-ops.h>
+#include <linux/set_memory.h>
 #include <asm/hyperv-tlfs.h>
 #include <asm/mshyperv.h>
 
@@ -359,6 +360,7 @@ int hv_common_cpu_init(unsigned int cpu)
 	u64 msr_vp_index;
 	gfp_t flags;
 	int pgcount = hv_root_partition ? 2 : 1;
+	int ret;
 
 	/* hv_cpu_init() can be called with IRQs disabled from hv_resume() */
 	flags = irqs_disabled() ? GFP_ATOMIC : GFP_KERNEL;
@@ -378,6 +380,17 @@ int hv_common_cpu_init(unsigned int cpu)
 			outputarg = (void **)this_cpu_ptr(hyperv_pcpu_output_arg);
 			*outputarg = (char *)(*inputarg) + HV_HYP_PAGE_SIZE;
 		}
+
+		if (hv_isolation_type_en_snp()) {
+			ret = set_memory_decrypted((unsigned long)*inputarg, pgcount);
+			if (ret) {
+				kfree(*inputarg);
+				*inputarg = NULL;
+				return ret;
+			}
+
+			memset(*inputarg, 0x00, pgcount * PAGE_SIZE);
+		}
 	}
 
 	msr_vp_index = hv_get_register(HV_REGISTER_VP_INDEX);