x86/sev: Add a helper for the PVALIDATE instruction

An SNP-active guest uses the PVALIDATE instruction to validate or
rescind the validation of a guest page’s RMP entry. Upon completion,
a return code is stored in EAX and rFLAGS bits are set based on the
return code. If the instruction completed successfully, the CF
indicates if the content of the RMP were changed or not.

See AMD APM Volume 3 for additional details.

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>

arch/x86/include/asm/sev.h

@@ -59,6 +59,16 @@ extern void vc_no_ghcb(void);
 extern void vc_boot_ghcb(void);
 extern bool handle_vc_boot_ghcb(struct pt_regs *regs);
 
+/* Return code of pvalidate */
+#define PVALIDATE_SUCCESS		0
+#define PVALIDATE_FAIL_INPUT		1
+#define PVALIDATE_FAIL_SIZEMISMATCH	6
+#define PVALIDATE_FAIL_NOUPDATE		255 /* Software defined (when rFlags.CF = 1) */
+
+/* RMP page size */
+#define RMP_PG_SIZE_2M			1
+#define RMP_PG_SIZE_4K			0
+
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 extern struct static_key_false sev_es_enable_key;
 extern void __sev_es_ist_enter(struct pt_regs *regs);
@@ -81,12 +91,29 @@ static __always_inline void sev_es_nmi_complete(void)
 		__sev_es_nmi_complete();
 }
 extern int __init sev_es_efi_map_ghcbs(pgd_t *pgd);
+static inline int pvalidate(unsigned long vaddr, bool rmp_psize, bool validate)
+{
+	bool no_rmpupdate;
+	int rc;
+
+	asm volatile(".byte 0xF2, 0x0F, 0x01, 0xFF\n\t"
+		     CC_SET(c)
+		     : CC_OUT(c) (no_rmpupdate), "=a"(rc)
+		     : "a"(vaddr), "c"(rmp_psize), "d"(validate)
+		     : "memory", "cc");
+
+	if (no_rmpupdate)
+		return PVALIDATE_FAIL_NOUPDATE;
+
+	return rc;
+}
 #else
 static inline void sev_es_ist_enter(struct pt_regs *regs) { }
 static inline void sev_es_ist_exit(void) { }
 static inline int sev_es_setup_ap_jump_table(struct real_mode_header *rmh) { return 0; }
 static inline void sev_es_nmi_complete(void) { }
 static inline int sev_es_efi_map_ghcbs(pgd_t *pgd) { return 0; }
+static inline int pvalidate(unsigned long vaddr, bool rmp_psize, bool validate) { return 0; }
 #endif
 
 #endif