[PATCH v2 09/12] x86/sev: Use AP Jump Table blob to stop CPU

Joerg Roedel
2021-09-13T15:56:29Z

From: Joerg Roedel <jroedel@suse.de>

To support kexec under SEV-ES the APs can't be parked with HLT. Upon
wakeup the AP needs to find its way to execute at the reset vector set
by the new kernel and in real-mode.

This is what the AP Jump Table blob provides, so stop the APs the
SEV-ES way by calling the AP-reset-hold VMGEXIT from the AP Jump
Table.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
arch/x86/include/asm/sev.h | 7 +++++++
arch/x86/kernel/process.c | 8 ++++++++
arch/x86/kernel/sev.c | 11 ++++++++++-
3 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 134a7c9d91b6..cd14b6e10f12 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -81,12 +81,19 @@ static __always_inline void sev_es_nmi_complete(void)
__sev_es_nmi_complete();
}
extern int __init sev_es_efi_map_ghcbs(pgd_t *pgd);
+void __sev_es_stop_this_cpu(void);
+static __always_inline void sev_es_stop_this_cpu(void)
+{
+ if (static_branch_unlikely(&sev_es_enable_key))
+ __sev_es_stop_this_cpu();
+}
#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 void sev_es_stop_this_cpu(void) { }
#endif

#endif
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 1d9463e3096b..8d9b03923baa 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -43,6 +43,7 @@
#include <asm/io_bitmap.h>
#include <asm/proto.h>
#include <asm/frame.h>
+#include <asm/sev.h>

#include "process.h"

@@ -752,6 +753,13 @@ void stop_this_cpu(void *dummy)
if (boot_cpu_has(X86_FEATURE_SME))
native_wbinvd();
for (;;) {
+ /*
+ * SEV-ES guests need a special stop routine to support
+ * kexec. Try this first, if it fails the function will
+ * return and native_halt() is used.
+ */
+ sev_es_stop_this_cpu();
+
/*
* Use native_halt() so that memory contents don't change
* (stack usage and variables) after possibly issuing the
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 20b439986d86..bac9bb4fa54e 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -695,7 +695,6 @@ static bool __init sev_es_setup_ghcb(void)
return true;
}

-#ifdef CONFIG_HOTPLUG_CPU
void __noreturn sev_jumptable_ap_park(void)
{
local_irq_disable();
@@ -725,6 +724,16 @@ void __noreturn sev_jumptable_ap_park(void)
}
STACK_FRAME_NON_STANDARD(sev_jumptable_ap_park);

+void __sev_es_stop_this_cpu(void)
+{
+ /* Only park in the AP Jump Table when the code has been installed */
+ if (!sev_ap_jumptable_blob_installed)
+ return;
+
+ sev_jumptable_ap_park();
+}
+
+#ifdef CONFIG_HOTPLUG_CPU
static void sev_es_ap_hlt_loop(void)
{
struct ghcb_state state;
--
2.33.0