[RFT PATCH v2 17/23] x86/sev: Move __sev_[get|put]_ghcb() into separate noinstr object

Ard Biesheuvel
2025-05-04T09:53:41Z

From: Ard Biesheuvel <ardb@kernel.org>

Rename sev-nmi.c to sev-noinstr.c, and move the get/put GHCB routines
into it too.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/boot/startup/sev-startup.c | 75 --------------------
arch/x86/coco/sev/Makefile | 6 +-
arch/x86/coco/sev/{sev-nmi.c => sev-noinstr.c} | 74 +++++++++++++++++++
3 files changed, 77 insertions(+), 78 deletions(-)

diff --git a/arch/x86/boot/startup/sev-startup.c b/arch/x86/boot/startup/sev-startup.c
index 2c2a5a043f18..6ba50723d546 100644
--- a/arch/x86/boot/startup/sev-startup.c
+++ b/arch/x86/boot/startup/sev-startup.c
@@ -41,84 +41,9 @@
#include <asm/cpuid.h>
#include <asm/cmdline.h>

-
-/*
- * Nothing shall interrupt this code path while holding the per-CPU
- * GHCB. The backup GHCB is only for NMIs interrupting this path.
- *
- * Callers must disable local interrupts around it.
- */
-noinstr struct ghcb *__sev_get_ghcb(struct ghcb_state *state)
-{
- struct sev_es_runtime_data *data;
- struct ghcb *ghcb;
-
- WARN_ON(!irqs_disabled());
-
- data = this_cpu_read(runtime_data);
- ghcb = &data->ghcb_page;
-
- if (unlikely(data->ghcb_active)) {
- /* GHCB is already in use - save its contents */
-
- if (unlikely(data->backup_ghcb_active)) {
- /*
- * Backup-GHCB is also already in use. There is no way
- * to continue here so just kill the machine. To make
- * panic() work, mark GHCBs inactive so that messages
- * can be printed out.
- */
- data->ghcb_active = false;
- data->backup_ghcb_active = false;
-
- instrumentation_begin();
- panic("Unable to handle #VC exception! GHCB and Backup GHCB are already in use");
- instrumentation_end();
- }
-
- /* Mark backup_ghcb active before writing to it */
- data->backup_ghcb_active = true;
-
- state->ghcb = &data->backup_ghcb;
-
- /* Backup GHCB content */
- *state->ghcb = *ghcb;
- } else {
- state->ghcb = NULL;
- data->ghcb_active = true;
- }
-
- return ghcb;
-}
-
/* Include code shared with pre-decompression boot stage */
#include "sev-shared.c"

-noinstr void __sev_put_ghcb(struct ghcb_state *state)
-{
- struct sev_es_runtime_data *data;
- struct ghcb *ghcb;
-
- WARN_ON(!irqs_disabled());
-
- data = this_cpu_read(runtime_data);
- ghcb = &data->ghcb_page;
-
- if (state->ghcb) {
- /* Restore GHCB from Backup */
- *ghcb = *state->ghcb;
- data->backup_ghcb_active = false;
- state->ghcb = NULL;
- } else {
- /*
- * Invalidate the GHCB so a VMGEXIT instruction issued
- * from userspace won't appear to be valid.
- */
- vc_ghcb_invalidate(ghcb);
- data->ghcb_active = false;
- }
-}
-
void __head
early_set_pages_state(unsigned long vaddr, unsigned long paddr,
unsigned long npages, enum psc_op op)
diff --git a/arch/x86/coco/sev/Makefile b/arch/x86/coco/sev/Makefile
index db3255b979bd..b348c9486315 100644
--- a/arch/x86/coco/sev/Makefile
+++ b/arch/x86/coco/sev/Makefile
@@ -1,9 +1,9 @@
# SPDX-License-Identifier: GPL-2.0

-obj-y += core.o sev-nmi.o vc-handle.o
+obj-y += core.o sev-noinstr.o vc-handle.o

# Clang 14 and older may fail to respect __no_sanitize_undefined when inlining
-UBSAN_SANITIZE_sev-nmi.o := n
+UBSAN_SANITIZE_sev-noinstr.o := n

# GCC may fail to respect __no_sanitize_address when inlining
-KASAN_SANITIZE_sev-nmi.o := n
+KASAN_SANITIZE_sev-noinstr.o := n
diff --git a/arch/x86/coco/sev/sev-nmi.c b/arch/x86/coco/sev/sev-noinstr.c
similarity index 61%
rename from arch/x86/coco/sev/sev-nmi.c
rename to arch/x86/coco/sev/sev-noinstr.c
index d8dfaddfb367..b527eafb6312 100644
--- a/arch/x86/coco/sev/sev-nmi.c
+++ b/arch/x86/coco/sev/sev-noinstr.c
@@ -106,3 +106,77 @@ void noinstr __sev_es_nmi_complete(void)

__sev_put_ghcb(&state);
}
+
+/*
+ * Nothing shall interrupt this code path while holding the per-CPU
+ * GHCB. The backup GHCB is only for NMIs interrupting this path.
+ *
+ * Callers must disable local interrupts around it.
+ */
+noinstr struct ghcb *__sev_get_ghcb(struct ghcb_state *state)
+{
+ struct sev_es_runtime_data *data;
+ struct ghcb *ghcb;
+
+ WARN_ON(!irqs_disabled());
+
+ data = this_cpu_read(runtime_data);
+ ghcb = &data->ghcb_page;
+
+ if (unlikely(data->ghcb_active)) {
+ /* GHCB is already in use - save its contents */
+
+ if (unlikely(data->backup_ghcb_active)) {
+ /*
+ * Backup-GHCB is also already in use. There is no way
+ * to continue here so just kill the machine. To make
+ * panic() work, mark GHCBs inactive so that messages
+ * can be printed out.
+ */
+ data->ghcb_active = false;
+ data->backup_ghcb_active = false;
+
+ instrumentation_begin();
+ panic("Unable to handle #VC exception! GHCB and Backup GHCB are already in use");
+ instrumentation_end();
+ }
+
+ /* Mark backup_ghcb active before writing to it */
+ data->backup_ghcb_active = true;
+
+ state->ghcb = &data->backup_ghcb;
+
+ /* Backup GHCB content */
+ *state->ghcb = *ghcb;
+ } else {
+ state->ghcb = NULL;
+ data->ghcb_active = true;
+ }
+
+ return ghcb;
+}
+
+noinstr void __sev_put_ghcb(struct ghcb_state *state)
+{
+ struct sev_es_runtime_data *data;
+ struct ghcb *ghcb;
+
+ WARN_ON(!irqs_disabled());
+
+ data = this_cpu_read(runtime_data);
+ ghcb = &data->ghcb_page;
+
+ if (state->ghcb) {
+ /* Restore GHCB from Backup */
+ *ghcb = *state->ghcb;
+ data->backup_ghcb_active = false;
+ state->ghcb = NULL;
+ } else {
+ /*
+ * Invalidate the GHCB so a VMGEXIT instruction issued
+ * from userspace won't appear to be valid.
+ */
+ vc_ghcb_invalidate(ghcb);
+ data->ghcb_active = false;
+ }
+}
--
2.49.0.906.g1f30a19c02-goog