Re: [PATCH v1 21/26] crypto: ccp: Add panic notifier for SEV/SNP firmware shutdown on kdump

[Borislav Petkov]

On Sat, Dec 30, 2023 at 10:19:49AM -0600, Michael Roth wrote:
> From: Ashish Kalra <ashish.kalra@xxxxxxx>
> 
> Add a kdump safe version of sev_firmware_shutdown() registered as a
> crash_kexec_post_notifier, which is invoked during panic/crash to do
> SEV/SNP shutdown. This is required for transitioning all IOMMU pages
> to reclaim/hypervisor state, otherwise re-init of IOMMU pages during
> crashdump kernel boot fails and panics the crashdump kernel. This
> panic notifier runs in atomic context, hence it ensures not to
> acquire any locks/mutexes and polls for PSP command completion
> instead of depending on PSP command completion interrupt.
> 
> Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> [mdr: remove use of "we" in comments]
> Signed-off-by: Michael Roth <michael.roth@xxxxxxx>

Cleanups ontop, see if the below works too. Especially:

* I've zapped the WBINVD before the TMR pages are freed because
__sev_snp_shutdown_locked() will WBINVD anyway.

* The mutex_is_locked() check in snp_shutdown_on_panic() is silly
because the panic notifier runs on one CPU anyway.

Thx.

---

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 435ba9bc4510..27323203e593 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -227,6 +227,7 @@ 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 kdump_sev_callback(void);
 #else
 static inline void sev_es_ist_enter(struct pt_regs *regs) { }
 static inline void sev_es_ist_exit(void) { }
@@ -255,6 +256,7 @@ 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 kdump_sev_callback(void) {  }
 #endif
 
 #ifdef CONFIG_KVM_AMD_SEV
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 23ede774d31b..64ae3a1e5c30 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -40,6 +40,7 @@
 #include <asm/intel_pt.h>
 #include <asm/crash.h>
 #include <asm/cmdline.h>
+#include <asm/sev.h>
 
 /* Used while preparing memory map entries for second kernel */
 struct crash_memmap_data {
@@ -59,12 +60,7 @@ static void kdump_nmi_callback(int cpu, struct pt_regs *regs)
 	 */
 	cpu_emergency_stop_pt();
 
-	/*
-	 * for SNP do wbinvd() on remote CPUs to
-	 * safely do SNP_SHUTDOWN on the local CPU.
-	 */
-	if (cpu_feature_enabled(X86_FEATURE_SEV_SNP))
-		wbinvd();
+	kdump_sev_callback();
 
 	disable_local_APIC();
 }
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index c67285824e82..dbb2cc6b5666 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -2262,3 +2262,13 @@ static int __init snp_init_platform_device(void)
 	return 0;
 }
 device_initcall(snp_init_platform_device);
+
+void kdump_sev_callback(void)
+{
+	/*
+	 * Do wbinvd() on remote CPUs when SNP is enabled in order to
+	 * safely do SNP_SHUTDOWN on the the local CPU.
+	 */
+	if (cpu_feature_enabled(X86_FEATURE_SEV_SNP))
+		wbinvd();
+}
diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 598878e760bc..c342e5e54e45 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -161,7 +161,6 @@ static int sev_wait_cmd_ioc(struct sev_device *sev,
 
 			udelay(10);
 		}
-
 		return -ETIMEDOUT;
 	}
 
@@ -1654,7 +1653,7 @@ static int sev_update_firmware(struct device *dev)
 	return ret;
 }
 
-static int __sev_snp_shutdown_locked(int *error, bool in_panic)
+static int __sev_snp_shutdown_locked(int *error, bool panic)
 {
 	struct sev_device *sev = psp_master->sev_data;
 	struct sev_data_snp_shutdown_ex data;
@@ -1673,7 +1672,7 @@ static int __sev_snp_shutdown_locked(int *error, bool in_panic)
 	 * In that case, a wbinvd() is done on remote CPUs via the NMI
 	 * callback, so only a local wbinvd() is needed here.
 	 */
-	if (!in_panic)
+	if (!panic)
 		wbinvd_on_all_cpus();
 	else
 		wbinvd();
@@ -2199,26 +2198,13 @@ int sev_dev_init(struct psp_device *psp)
 	return ret;
 }
 
-static void __sev_firmware_shutdown(struct sev_device *sev, bool in_panic)
+static void __sev_firmware_shutdown(struct sev_device *sev, bool panic)
 {
 	int error;
 
 	__sev_platform_shutdown_locked(NULL);
 
 	if (sev_es_tmr) {
-		/*
-		 * The TMR area was encrypted, flush it from the cache
-		 *
-		 * If invoked during panic handling, local interrupts are
-		 * disabled and all CPUs are stopped, so wbinvd_on_all_cpus()
-		 * can't be used. In that case, wbinvd() is done on remote CPUs
-		 * via the NMI callback, so a local wbinvd() is sufficient here.
-		 */
-		if (!in_panic)
-			wbinvd_on_all_cpus();
-		else
-			wbinvd();
-
 		__snp_free_firmware_pages(virt_to_page(sev_es_tmr),
 					  get_order(sev_es_tmr_size),
 					  true);
@@ -2237,7 +2223,7 @@ static void __sev_firmware_shutdown(struct sev_device *sev, bool in_panic)
 		snp_range_list = NULL;
 	}
 
-	__sev_snp_shutdown_locked(&error, in_panic);
+	__sev_snp_shutdown_locked(&error, panic);
 }
 
 static void sev_firmware_shutdown(struct sev_device *sev)
@@ -2262,26 +2248,18 @@ void sev_dev_destroy(struct psp_device *psp)
 	psp_clear_sev_irq_handler(psp);
 }
 
-static int sev_snp_shutdown_on_panic(struct notifier_block *nb,
-				     unsigned long reason, void *arg)
+static int snp_shutdown_on_panic(struct notifier_block *nb,
+				 unsigned long reason, void *arg)
 {
 	struct sev_device *sev = psp_master->sev_data;
 
-	/*
-	 * Panic callbacks are executed with all other CPUs stopped,
-	 * so don't wait for sev_cmd_mutex to be released since it
-	 * would block here forever.
-	 */
-	if (mutex_is_locked(&sev_cmd_mutex))
-		return NOTIFY_DONE;
-
 	__sev_firmware_shutdown(sev, true);
 
 	return NOTIFY_DONE;
 }
 
-static struct notifier_block sev_snp_panic_notifier = {
-	.notifier_call = sev_snp_shutdown_on_panic,
+static struct notifier_block snp_panic_notifier = {
+	.notifier_call = snp_shutdown_on_panic,
 };
 
 int sev_issue_cmd_external_user(struct file *filep, unsigned int cmd,
@@ -2322,7 +2300,7 @@ void sev_pci_init(void)
 		"-SNP" : "", sev->api_major, sev->api_minor, sev->build);
 
 	atomic_notifier_chain_register(&panic_notifier_list,
-				       &sev_snp_panic_notifier);
+				       &snp_panic_notifier);
 	return;
 
 err:
@@ -2339,5 +2317,5 @@ void sev_pci_exit(void)
 	sev_firmware_shutdown(sev);
 
 	atomic_notifier_chain_unregister(&panic_notifier_list,
-					 &sev_snp_panic_notifier);
+					 &snp_panic_notifier);
 }

-- 
Regards/Gruss,
    Boris.

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