crypto: ccp: Add panic notifier for SEV/SNP firmware shutdown on kdump

Add a kdump safe version of sev_firmware_shutdown() and register it as a
crash_kexec_post_notifier so it will be 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.

  [ mdr: Remove use of "we" in comments. ]

Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240126041126.1927228-21-michael.roth@amd.com

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 {
@@ -59,6 +60,8 @@ static void kdump_nmi_callback(int cpu, struct pt_regs *regs)
 	 */
 	cpu_emergency_stop_pt();
 
+	kdump_sev_callback();
+
 	disable_local_APIC();
 }