linux-kernel - [PATCH v4 6/9] x86/sev: Use AP Jump Table blob to stop CPU

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Date: Mon, 11 Mar 2024 17:17:24 +0100
From: Vasant Karasulli <vsntk18@...il.com>
To: x86@...nel.org
Cc: joro@...tes.org,
	cfir@...gle.com,
	dan.j.williams@...el.com,
	dave.hansen@...ux.intel.com,
	ebiederm@...ssion.com,
	erdemaktas@...gle.com,
	hpa@...or.com,
	jgross@...e.com,
	jslaby@...e.cz,
	keescook@...omium.org,
	kexec@...ts.infradead.org,
	kvm@...r.kernel.org,
	linux-coco@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	luto@...nel.org,
	martin.b.radev@...il.com,
	mhiramat@...nel.org,
	mstunes@...are.com,
	nivedita@...m.mit.edu,
	peterz@...radead.org,
	rientjes@...gle.com,
	seanjc@...gle.com,
	stable@...r.kernel.org,
	thomas.lendacky@....com,
	virtualization@...ts.linux-foundation.org,
	Joerg Roedel <jroedel@...e.de>,
	Vasant Karasulli <vkarasulli@...e.de>
Subject: [PATCH v4 6/9] 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 c48db0bfb707..2dbd2238325a 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -216,6 +216,7 @@ int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, struct sn
 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_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) { }
@@ -244,6 +245,7 @@ static inline int snp_issue_guest_request(u64 exit_code, struct snp_req_data *in
 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_es_stop_this_cpu(void) { }
 #endif

 #endif
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index ab49ade31b0d..ddc3fa076f4d 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 08bf897361b9..10f4294904b4 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -1350,7 +1350,6 @@ 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();
@@ -1383,6 +1382,20 @@ 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