x86/sev: Provide support for SNP guest request NAEs

Version 2 of GHCB specification provides SNP_GUEST_REQUEST and
SNP_EXT_GUEST_REQUEST NAE that can be used by the SNP guest to
communicate with the PSP.

While at it, add a snp_issue_guest_request() helper that will be used by
driver or other subsystem to issue the request to PSP.

See SEV-SNP firmware and GHCB spec for more details.
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220307213356.2797205-42-brijesh.singh@amd.com

arch/x86/include/asm/sev-common.h

@@ -128,6 +128,9 @@ struct snp_psc_desc {
 	struct psc_entry entries[VMGEXIT_PSC_MAX_ENTRY];
 } __packed;
 
+/* Guest message request error code */
+#define SNP_GUEST_REQ_INVALID_LEN	BIT_ULL(32)
+
 #define GHCB_MSR_TERM_REQ		0x100
 #define GHCB_MSR_TERM_REASON_SET_POS	12
 #define GHCB_MSR_TERM_REASON_SET_MASK	0xf

arch/x86/include/asm/sev.h

@@ -87,6 +87,14 @@ extern bool handle_vc_boot_ghcb(struct pt_regs *regs);
 
 #define RMPADJUST_VMSA_PAGE_BIT		BIT(16)
 
+/* SNP Guest message request */
+struct snp_req_data {
+	unsigned long req_gpa;
+	unsigned long resp_gpa;
+	unsigned long data_gpa;
+	unsigned int data_npages;
+};
+
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 extern struct static_key_false sev_es_enable_key;
 extern void __sev_es_ist_enter(struct pt_regs *regs);
@@ -154,6 +162,7 @@ void snp_set_memory_private(unsigned long vaddr, unsigned int npages);
 void snp_set_wakeup_secondary_cpu(void);
 bool snp_init(struct boot_params *bp);
 void snp_abort(void);
+int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned long *fw_err);
 #else
 static inline void sev_es_ist_enter(struct pt_regs *regs) { }
 static inline void sev_es_ist_exit(void) { }
@@ -173,6 +182,11 @@ static inline void snp_set_memory_private(unsigned long vaddr, unsigned int npag
 static inline void snp_set_wakeup_secondary_cpu(void) { }
 static inline bool snp_init(struct boot_params *bp) { return false; }
 static inline void snp_abort(void) { }
+static inline int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input,
+					  unsigned long *fw_err)
+{
+	return -ENOTTY;
+}
 #endif
 
 #endif

arch/x86/include/uapi/asm/svm.h

@@ -109,6 +109,8 @@
 #define SVM_VMGEXIT_SET_AP_JUMP_TABLE		0
 #define SVM_VMGEXIT_GET_AP_JUMP_TABLE		1
 #define SVM_VMGEXIT_PSC				0x80000010
+#define SVM_VMGEXIT_GUEST_REQUEST		0x80000011
+#define SVM_VMGEXIT_EXT_GUEST_REQUEST		0x80000012
 #define SVM_VMGEXIT_AP_CREATION			0x80000013
 #define SVM_VMGEXIT_AP_CREATE_ON_INIT		0
 #define SVM_VMGEXIT_AP_CREATE			1
@@ -225,6 +227,8 @@
 	{ SVM_VMGEXIT_AP_HLT_LOOP,	"vmgexit_ap_hlt_loop" }, \
 	{ SVM_VMGEXIT_AP_JUMP_TABLE,	"vmgexit_ap_jump_table" }, \
 	{ SVM_VMGEXIT_PSC,		"vmgexit_page_state_change" }, \
+	{ SVM_VMGEXIT_GUEST_REQUEST,	"vmgexit_guest_request" }, \
+	{ SVM_VMGEXIT_EXT_GUEST_REQUEST, "vmgexit_ext_guest_request" }, \
 	{ SVM_VMGEXIT_AP_CREATION,	"vmgexit_ap_creation" }, \
 	{ SVM_VMGEXIT_HV_FEATURES,	"vmgexit_hypervisor_feature" }, \
 	{ SVM_EXIT_ERR,         "invalid_guest_state" }

arch/x86/kernel/sev.c

@@ -2106,3 +2106,60 @@ static int __init init_sev_config(char *str)
 	return 1;
 }
 __setup("sev=", init_sev_config);
+
+int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned long *fw_err)
+{
+	struct ghcb_state state;
+	struct es_em_ctxt ctxt;
+	unsigned long flags;
+	struct ghcb *ghcb;
+	int ret;
+
+	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
+		return -ENODEV;
+
+	if (!fw_err)
+		return -EINVAL;
+
+	/*
+	 * __sev_get_ghcb() needs to run with IRQs disabled because it is using
+	 * a per-CPU GHCB.
+	 */
+	local_irq_save(flags);
+
+	ghcb = __sev_get_ghcb(&state);
+	if (!ghcb) {
+		ret = -EIO;
+		goto e_restore_irq;
+	}
+
+	vc_ghcb_invalidate(ghcb);
+
+	if (exit_code == SVM_VMGEXIT_EXT_GUEST_REQUEST) {
+		ghcb_set_rax(ghcb, input->data_gpa);
+		ghcb_set_rbx(ghcb, input->data_npages);
+	}
+
+	ret = sev_es_ghcb_hv_call(ghcb, true, &ctxt, exit_code, input->req_gpa, input->resp_gpa);
+	if (ret)
+		goto e_put;
+
+	if (ghcb->save.sw_exit_info_2) {
+		/* Number of expected pages are returned in RBX */
+		if (exit_code == SVM_VMGEXIT_EXT_GUEST_REQUEST &&
+		    ghcb->save.sw_exit_info_2 == SNP_GUEST_REQ_INVALID_LEN)
+			input->data_npages = ghcb_get_rbx(ghcb);
+
+		*fw_err = ghcb->save.sw_exit_info_2;
+
+		ret = -EIO;
+	}
+
+e_put:
+	__sev_put_ghcb(&state);
+e_restore_irq:
+	local_irq_restore(flags);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(snp_issue_guest_request);