[PATCH v7 09/22] x86/sev: Use boot SVSM CA for all startup and init code

Ard Biesheuvel
2025-08-28T10:22:46Z

From: Ard Biesheuvel <ardb@kernel.org>

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 CPU #0.

This removes the need to make the per-CPU variables and associated state
in sev_cfg accessible to the startup code once confined.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/boot/compressed/sev.c | 13 ------
arch/x86/boot/startup/sev-startup.c | 11 ++---
arch/x86/coco/sev/core.c | 47 +++++++++-----------
arch/x86/include/asm/sev-internal.h | 16 -------
4 files changed, 28 insertions(+), 59 deletions(-)

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index dffe607e6d8b..de73da526577 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -37,19 +37,6 @@ struct ghcb *boot_ghcb;

#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 */
diff --git a/arch/x86/boot/startup/sev-startup.c b/arch/x86/boot/startup/sev-startup.c
index 8009a37d53c1..b0fc63f8dee1 100644
--- a/arch/x86/boot/startup/sev-startup.c
+++ b/arch/x86/boot/startup/sev-startup.c
@@ -50,9 +50,6 @@ u64 sev_secrets_pa __ro_after_init;
/* 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.
@@ -153,7 +150,9 @@ void __head early_snp_set_memory_private(unsigned long vaddr, unsigned long padd
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
};

/*
@@ -176,7 +175,9 @@ void __head early_snp_set_memory_shared(unsigned long vaddr, unsigned long paddr
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
};

/*
diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index a833b2b31d3d..9782ebe30675 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -46,6 +46,25 @@
#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
@@ -1312,7 +1331,8 @@ static void __init alloc_runtime_data(int cpu)
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);
@@ -1366,32 +1386,9 @@ void __init sev_es_init_vc_handling(void)
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();

/* Secondary CPUs use the runtime #VC handler */
diff --git a/arch/x86/include/asm/sev-internal.h b/arch/x86/include/asm/sev-internal.h
index 9ff824540b48..f98f080410ad 100644
--- a/arch/x86/include/asm/sev-internal.h
+++ b/arch/x86/include/asm/sev-internal.h
@@ -62,22 +62,6 @@ DECLARE_PER_CPU(u64, svsm_caa_pa);

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);

--
2.51.0.268.g9569e192d0-goog