KVM: SEV: Do cache maintenance on the source VM during intra-host migrationgrafted

Manually perform cache maintenance on the source VM during intra-host
migration to ensure no stale data is left in CPU caches after the VM is
destroyed.  Because the source VM is "converted" to a non-SEV VM, KVM's
memory reclaim flows won't trigger cache maintenance, e.g. when all guest
memory is reclaimed in response to detaching from the mmu_notifier.

Note, relying on the destination VM to do cache maintenance isn't an option
as KVM doesn't require identical guest memory configurations, i.e. the
source VM may have access to memory that the destination VM does not.
Enforcing equivalent memory configurations is infeasible, as it would
require a *deep* comparison of memslots, e.g. to verify that not only are
the memslot identical, but what the memslots point at is also identical.

Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration")
Cc: stable@vger.kernel.org
Reported-by: Stefan Teodorescu <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260923163721.1584779-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 131 insertions, 0 deletions

diff --git a/lib/dump_stack.c b/lib/dump_stack.c
new file mode 100644
index 000000000..f0c78b5b5
--- /dev/null
+++ b/lib/dump_stack.c
@@ -0,0 +1,131 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Provide a default dump_stack() function for architectures
+ * which don't implement their own.
+ */
+
+#include <linux/kernel.h>
+#include <linux/buildid.h>
+#include <linux/export.h>
+#include <linux/sched.h>
+#include <linux/sched/debug.h>
+#include <linux/smp.h>
+#include <linux/atomic.h>
+#include <linux/kexec.h>
+#include <linux/utsname.h>
+#include <linux/stop_machine.h>
+
+static char dump_stack_arch_desc_str[128];
+
+/**
+ * dump_stack_set_arch_desc - set arch-specific str to show with task dumps
+ * @fmt: printf-style format string
+ * @...: arguments for the format string
+ *
+ * The configured string will be printed right after utsname during task
+ * dumps.  Usually used to add arch-specific system identifiers.  If an
+ * arch wants to make use of such an ID string, it should initialize this
+ * as soon as possible during boot.
+ */
+void __init dump_stack_set_arch_desc(const char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	vsnprintf(dump_stack_arch_desc_str, sizeof(dump_stack_arch_desc_str),
+		  fmt, args);
+	va_end(args);
+}
+
+#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
+#define BUILD_ID_FMT " %20phN"
+#define BUILD_ID_VAL vmlinux_build_id
+#else
+#define BUILD_ID_FMT "%s"
+#define BUILD_ID_VAL ""
+#endif
+
+/**
+ * dump_stack_print_info - print generic debug info for dump_stack()
+ * @log_lvl: log level
+ *
+ * Arch-specific dump_stack() implementations can use this function to
+ * print out the same debug information as the generic dump_stack().
+ */
+void dump_stack_print_info(const char *log_lvl)
+{
+	printk("%sCPU: %d UID: %u PID: %d Comm: %.20s %s%s %s %.*s %s " BUILD_ID_FMT "\n",
+	       log_lvl, raw_smp_processor_id(),
+	       __kuid_val(current_real_cred()->euid),
+	       current->pid, current->comm,
+	       kexec_crash_loaded() ? "Kdump: loaded " : "",
+	       print_tainted(),
+	       init_utsname()->release,
+	       (int)strcspn(init_utsname()->version, " "),
+	       init_utsname()->version, preempt_model_str(), BUILD_ID_VAL);
+
+	if (get_taint())
+		printk("%s%s\n", log_lvl, print_tainted_verbose());
+
+	if (dump_stack_arch_desc_str[0] != '\0')
+		printk("%sHardware name: %s\n",
+		       log_lvl, dump_stack_arch_desc_str);
+
+	print_worker_info(log_lvl, current);
+	print_stop_info(log_lvl, current);
+	print_scx_info(log_lvl, current);
+}
+
+/**
+ * show_regs_print_info - print generic debug info for show_regs()
+ * @log_lvl: log level
+ *
+ * show_regs() implementations can use this function to print out generic
+ * debug information.
+ */
+void show_regs_print_info(const char *log_lvl)
+{
+	dump_stack_print_info(log_lvl);
+}
+
+static void __dump_stack(const char *log_lvl)
+{
+	dump_stack_print_info(log_lvl);
+	show_stack(NULL, NULL, log_lvl);
+}
+
+/**
+ * dump_stack_lvl - dump the current task information and its stack trace
+ * @log_lvl: log level
+ *
+ * Architectures can override this implementation by implementing its own.
+ */
+asmlinkage __visible void dump_stack_lvl(const char *log_lvl)
+{
+	bool in_panic = panic_on_this_cpu();
+	unsigned long flags;
+
+	/*
+	 * Permit this cpu to perform nested stack dumps while serialising
+	 * against other CPUs, unless this CPU is in panic.
+	 *
+	 * When in panic, non-panic CPUs are not permitted to store new
+	 * printk messages so there is no need to synchronize the output.
+	 * This avoids potential deadlock in panic() if another CPU is
+	 * holding and unable to release the printk_cpu_sync.
+	 */
+	if (!in_panic)
+		printk_cpu_sync_get_irqsave(flags);
+
+	__dump_stack(log_lvl);
+
+	if (!in_panic)
+		printk_cpu_sync_put_irqrestore(flags);
+}
+EXPORT_SYMBOL(dump_stack_lvl);
+
+asmlinkage __visible void dump_stack(void)
+{
+	dump_stack_lvl(KERN_DEFAULT);
+}
+EXPORT_SYMBOL(dump_stack);