linux-kernel - [PATCH v6 06/10] x86/sev: Use AP Jump Table blob to stop CPU

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Message-Id: <20240610102113.20969-7-vsntk18@gmail.com>
Date: Mon, 10 Jun 2024 12:21:09 +0200
From: vsntk18@...il.com
To: vsntk18@...il.com
Cc: x86@...nel.org,
	Borislav.Petkov@....com,
	Dhaval.Giani@....com,
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Subject: [PATCH v6 06/10] x86/sev: Use AP Jump Table blob to stop CPU

From: Joerg Roedel <jroedel@...e.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@...e.de>
Signed-off-by: Vasant Karasulli <vkarasulli@...e.de>
---
 arch/x86/include/asm/sev.h |  2 ++
 arch/x86/kernel/process.c  |  8 ++++++++
 arch/x86/kernel/sev.c      | 15 ++++++++++++++-
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 963d51dcf0e6..6f681ced6594 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -232,6 +232,7 @@ void snp_accept_memory(phys_addr_t start, phys_addr_t end);
 u64 snp_get_unsupported_features(u64 status);
 u64 sev_get_status(void);
 void sev_show_status(void);
+void sev_es_stop_this_cpu(void);
 #else
 static inline void sev_es_ist_enter(struct pt_regs *regs) { }
 static inline void sev_es_ist_exit(void) { }
@@ -261,6 +262,7 @@ static inline void snp_accept_memory(phys_addr_t start, phys_addr_t end) { }
 static inline u64 snp_get_unsupported_features(u64 status) { return 0; }
 static inline u64 sev_get_status(void) { return 0; }
 static inline void sev_show_status(void) { }
+static inline void sev_es_stop_this_cpu(void) { }
 #endif
 
 #ifdef CONFIG_KVM_AMD_SEV
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index b8441147eb5e..0bc615d69c0e 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -52,6 +52,7 @@
 #include <asm/tdx.h>
 #include <asm/mmu_context.h>
 #include <asm/shstk.h>
+#include <asm/sev.h>
 
 #include "process.h"
 
@@ -836,6 +837,13 @@ void __noreturn stop_this_cpu(void *dummy)
 	cpumask_clear_cpu(cpu, &cpus_stop_mask);
 
 	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 84b79630f065..8d3cc5cd7e11 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -1357,7 +1357,6 @@ void setup_ghcb(void)
 		snp_register_ghcb_early(__pa(&boot_ghcb_page));
 }
 
-#ifdef CONFIG_HOTPLUG_CPU
 void __noreturn sev_jumptable_ap_park(void)
 {
 	local_irq_disable();
@@ -1390,6 +1389,20 @@ void __noreturn sev_jumptable_ap_park(void)
 }
 STACK_FRAME_NON_STANDARD(sev_jumptable_ap_park);
 
+void sev_es_stop_this_cpu(void)
+{
+	if (!(cc_vendor == CC_VENDOR_AMD) ||
+	    !cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT))
+		return;
+
+	/* 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;
-- 
2.34.1