x86/sev: Use boot SVSM CA for all startup and init code

To avoid having to reason about whether or not to use the per-CPU SVSM calling
area when running startup and init code on the boot CPU, reuse the boot SVSM
calling area as the per-CPU area for the BSP.

Thus, remove the need to make the per-CPU variables and associated state in
sev_cfg accessible to the startup code once confined.

[ bp: Massage commit message. ]

Signed-off-by: Ard Biesheuvel <[e-mail]>
Signed-off-by: Borislav Petkov (AMD) <[e-mail]>
Link: https://lore.kernel.org/[e-mail]

arch/x86/boot/compressed/sev.c

···
 
 #define __BOOT_COMPRESSED
 
-extern u64 boot_svsm_caa_pa;
-
-struct svsm_ca *svsm_get_caa(void)
-{
-	/* The decompressor is mapped 1:1 so VA == PA */
-	return (struct svsm_ca *)boot_svsm_caa_pa;
-}
-
-u64 svsm_get_caa_pa(void)
-{
-	return boot_svsm_caa_pa;
-}
-
 u8 snp_vmpl;
 
 /* Include code for early handlers */

arch/x86/boot/startup/sev-startup.c

···
 /* For early boot SVSM communication */
 struct svsm_ca boot_svsm_ca_page __aligned(PAGE_SIZE);
 
-DEFINE_PER_CPU(struct svsm_ca *, svsm_caa);
-DEFINE_PER_CPU(u64, svsm_caa_pa);
-
 /*
  * Nothing shall interrupt this code path while holding the per-CPU
  * GHCB. The backup GHCB is only for NMIs interrupting this path.
···
 					 unsigned long npages)
 {
 	struct psc_desc d = {
-		SNP_PAGE_STATE_PRIVATE, svsm_get_caa(), svsm_get_caa_pa()
+		SNP_PAGE_STATE_PRIVATE,
+		rip_rel_ptr(&boot_svsm_ca_page),
+		boot_svsm_caa_pa
 	};
 
 	/*
···
 					unsigned long npages)
 {
 	struct psc_desc d = {
-		SNP_PAGE_STATE_SHARED, svsm_get_caa(), svsm_get_caa_pa()
+		SNP_PAGE_STATE_SHARED,
+		rip_rel_ptr(&boot_svsm_ca_page),
+		boot_svsm_caa_pa
 	};
 
 	/*

arch/x86/coco/sev/core.c

···
 #include <asm/cmdline.h>
 #include <asm/msr.h>
 
+DEFINE_PER_CPU(struct svsm_ca *, svsm_caa);
+DEFINE_PER_CPU(u64, svsm_caa_pa);
+
+static inline struct svsm_ca *svsm_get_caa(void)
+{
+	if (sev_cfg.use_cas)
+		return this_cpu_read(svsm_caa);
+	else
+		return rip_rel_ptr(&boot_svsm_ca_page);
+}
+
+static inline u64 svsm_get_caa_pa(void)
+{
+	if (sev_cfg.use_cas)
+		return this_cpu_read(svsm_caa_pa);
+	else
+		return boot_svsm_caa_pa;
+}
+
 /* AP INIT values as documented in the APM2  section "Processor Initialization State" */
 #define AP_INIT_CS_LIMIT		0xffff
 #define AP_INIT_DS_LIMIT		0xffff
···
 		struct svsm_ca *caa;
 
 		/* Allocate the SVSM CA page if an SVSM is present */
-		caa = memblock_alloc_or_panic(sizeof(*caa), PAGE_SIZE);
+		caa = cpu ? memblock_alloc_or_panic(sizeof(*caa), PAGE_SIZE)
+			  : &boot_svsm_ca_page;
 
 		per_cpu(svsm_caa, cpu) = caa;
 		per_cpu(svsm_caa_pa, cpu) = __pa(caa);
···
 		init_ghcb(cpu);
 	}
 
-	/* If running under an SVSM, switch to the per-cpu CA */
-	if (snp_vmpl) {
-		struct svsm_call call = {};
-		unsigned long flags;
-		int ret;
-
-		local_irq_save(flags);
-
-		/*
-		 * SVSM_CORE_REMAP_CA call:
-		 *   RAX = 0 (Protocol=0, CallID=0)
-		 *   RCX = New CA GPA
-		 */
-		call.caa = svsm_get_caa();
-		call.rax = SVSM_CORE_CALL(SVSM_CORE_REMAP_CA);
-		call.rcx = this_cpu_read(svsm_caa_pa);
-		ret = svsm_perform_call_protocol(&call);
-		if (ret)
-			panic("Can't remap the SVSM CA, ret=%d, rax_out=0x%llx\n",
-			      ret, call.rax_out);
-
+	if (snp_vmpl)
 		sev_cfg.use_cas = true;
-
-		local_irq_restore(flags);
-	}
 
 	sev_es_setup_play_dead();
 

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

···
 
 extern u64 boot_svsm_caa_pa;
 
-static __always_inline struct svsm_ca *svsm_get_caa(void)
-{
-	if (sev_cfg.use_cas)
-		return this_cpu_read(svsm_caa);
-	else
-		return rip_rel_ptr(&boot_svsm_ca_page);
-}
-
-static __always_inline u64 svsm_get_caa_pa(void)
-{
-	if (sev_cfg.use_cas)
-		return this_cpu_read(svsm_caa_pa);
-	else
-		return boot_svsm_caa_pa;
-}
-
 enum es_result verify_exception_info(struct ghcb *ghcb, struct es_em_ctxt *ctxt);
 void vc_forward_exception(struct es_em_ctxt *ctxt);