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

[Joerg Roedel]

From: Joerg Roedel <jroe...@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 <jroe...@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 5e1f38179f49..c5da02f9100f 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"
 
@@ -736,6 +737,13 @@ 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 2147ebd0e919..5fdfa94c823c 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
 static void __noreturn sev_jumptable_ap_park(void)
 {
        local_irq_disable();
@@ -725,6 +724,16 @@ static 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;
-- 
2.31.1

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