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, 213 insertions, 0 deletions

diff --git a/arch/powerpc/kvm/timing.c b/arch/powerpc/kvm/timing.c
new file mode 100644
index 000000000..25071331f
--- /dev/null
+++ b/arch/powerpc/kvm/timing.c
@@ -0,0 +1,213 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *
+ * Copyright IBM Corp. 2008
+ *
+ * Authors: Hollis Blanchard <hollisb@us.ibm.com>
+ *          Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
+ */
+
+#include <linux/kvm_host.h>
+#include <linux/fs.h>
+#include <linux/seq_file.h>
+#include <linux/debugfs.h>
+#include <linux/uaccess.h>
+#include <linux/module.h>
+
+#include <asm/time.h>
+#include <asm-generic/div64.h>
+
+#include "timing.h"
+
+void kvmppc_init_timing_stats(struct kvm_vcpu *vcpu)
+{
+	int i;
+
+	/* Take a lock to avoid concurrent updates */
+	mutex_lock(&vcpu->arch.exit_timing_lock);
+
+	vcpu->arch.last_exit_type = 0xDEAD;
+	for (i = 0; i < __NUMBER_OF_KVM_EXIT_TYPES; i++) {
+		vcpu->arch.timing_count_type[i] = 0;
+		vcpu->arch.timing_max_duration[i] = 0;
+		vcpu->arch.timing_min_duration[i] = 0xFFFFFFFF;
+		vcpu->arch.timing_sum_duration[i] = 0;
+		vcpu->arch.timing_sum_quad_duration[i] = 0;
+	}
+	vcpu->arch.timing_last_exit = 0;
+	vcpu->arch.timing_exit.tv64 = 0;
+	vcpu->arch.timing_last_enter.tv64 = 0;
+
+	mutex_unlock(&vcpu->arch.exit_timing_lock);
+}
+
+static void add_exit_timing(struct kvm_vcpu *vcpu, u64 duration, int type)
+{
+	u64 old;
+
+	mutex_lock(&vcpu->arch.exit_timing_lock);
+
+	vcpu->arch.timing_count_type[type]++;
+
+	/* sum */
+	old = vcpu->arch.timing_sum_duration[type];
+	vcpu->arch.timing_sum_duration[type] += duration;
+	if (unlikely(old > vcpu->arch.timing_sum_duration[type])) {
+		printk(KERN_ERR"%s - wrap adding sum of durations"
+			" old %lld new %lld type %d exit # of type %d\n",
+			__func__, old, vcpu->arch.timing_sum_duration[type],
+			type, vcpu->arch.timing_count_type[type]);
+	}
+
+	/* square sum */
+	old = vcpu->arch.timing_sum_quad_duration[type];
+	vcpu->arch.timing_sum_quad_duration[type] += (duration*duration);
+	if (unlikely(old > vcpu->arch.timing_sum_quad_duration[type])) {
+		printk(KERN_ERR"%s - wrap adding sum of squared durations"
+			" old %lld new %lld type %d exit # of type %d\n",
+			__func__, old,
+			vcpu->arch.timing_sum_quad_duration[type],
+			type, vcpu->arch.timing_count_type[type]);
+	}
+
+	/* set min/max */
+	if (unlikely(duration < vcpu->arch.timing_min_duration[type]))
+		vcpu->arch.timing_min_duration[type] = duration;
+	if (unlikely(duration > vcpu->arch.timing_max_duration[type]))
+		vcpu->arch.timing_max_duration[type] = duration;
+
+	mutex_unlock(&vcpu->arch.exit_timing_lock);
+}
+
+void kvmppc_update_timing_stats(struct kvm_vcpu *vcpu)
+{
+	u64 exit = vcpu->arch.timing_last_exit;
+	u64 enter = vcpu->arch.timing_last_enter.tv64;
+
+	/* save exit time, used next exit when the reenter time is known */
+	vcpu->arch.timing_last_exit = vcpu->arch.timing_exit.tv64;
+
+	if (unlikely(vcpu->arch.last_exit_type == 0xDEAD || exit == 0))
+		return; /* skip incomplete cycle (e.g. after reset) */
+
+	/* update statistics for average and standard deviation */
+	add_exit_timing(vcpu, (enter - exit), vcpu->arch.last_exit_type);
+	/* enter -> timing_last_exit is time spent in guest - log this too */
+	add_exit_timing(vcpu, (vcpu->arch.timing_last_exit - enter),
+			TIMEINGUEST);
+}
+
+static const char *kvm_exit_names[__NUMBER_OF_KVM_EXIT_TYPES] = {
+	[MMIO_EXITS] =              "MMIO",
+	[SIGNAL_EXITS] =            "SIGNAL",
+	[ITLB_REAL_MISS_EXITS] =    "ITLBREAL",
+	[ITLB_VIRT_MISS_EXITS] =    "ITLBVIRT",
+	[DTLB_REAL_MISS_EXITS] =    "DTLBREAL",
+	[DTLB_VIRT_MISS_EXITS] =    "DTLBVIRT",
+	[SYSCALL_EXITS] =           "SYSCALL",
+	[ISI_EXITS] =               "ISI",
+	[DSI_EXITS] =               "DSI",
+	[EMULATED_INST_EXITS] =     "EMULINST",
+	[EMULATED_MTMSRWE_EXITS] =  "EMUL_WAIT",
+	[EMULATED_WRTEE_EXITS] =    "EMUL_WRTEE",
+	[EMULATED_MTSPR_EXITS] =    "EMUL_MTSPR",
+	[EMULATED_MFSPR_EXITS] =    "EMUL_MFSPR",
+	[EMULATED_MTMSR_EXITS] =    "EMUL_MTMSR",
+	[EMULATED_MFMSR_EXITS] =    "EMUL_MFMSR",
+	[EMULATED_TLBSX_EXITS] =    "EMUL_TLBSX",
+	[EMULATED_TLBWE_EXITS] =    "EMUL_TLBWE",
+	[EMULATED_RFI_EXITS] =      "EMUL_RFI",
+	[DEC_EXITS] =               "DEC",
+	[EXT_INTR_EXITS] =          "EXTINT",
+	[HALT_WAKEUP] =             "HALT",
+	[USR_PR_INST] =             "USR_PR_INST",
+	[FP_UNAVAIL] =              "FP_UNAVAIL",
+	[DEBUG_EXITS] =             "DEBUG",
+	[TIMEINGUEST] =             "TIMEINGUEST"
+};
+
+static int kvmppc_exit_timing_show(struct seq_file *m, void *private)
+{
+	struct kvm_vcpu *vcpu = m->private;
+	int i;
+	u64 min, max, sum, sum_quad;
+
+	seq_puts(m, "type	count	min	max	sum	sum_squared\n");
+
+	for (i = 0; i < __NUMBER_OF_KVM_EXIT_TYPES; i++) {
+
+		min = vcpu->arch.timing_min_duration[i];
+		do_div(min, tb_ticks_per_usec);
+		max = vcpu->arch.timing_max_duration[i];
+		do_div(max, tb_ticks_per_usec);
+		sum = vcpu->arch.timing_sum_duration[i];
+		do_div(sum, tb_ticks_per_usec);
+		sum_quad = vcpu->arch.timing_sum_quad_duration[i];
+		do_div(sum_quad, tb_ticks_per_usec);
+
+		seq_printf(m, "%12s	%10d	%10lld	%10lld	%20lld	%20lld\n",
+			kvm_exit_names[i],
+			vcpu->arch.timing_count_type[i],
+			min,
+			max,
+			sum,
+			sum_quad);
+
+	}
+	return 0;
+}
+
+/* Write 'c' to clear the timing statistics. */
+static ssize_t kvmppc_exit_timing_write(struct file *file,
+				       const char __user *user_buf,
+				       size_t count, loff_t *ppos)
+{
+	int err = -EINVAL;
+	char c;
+
+	if (count > 1) {
+		goto done;
+	}
+
+	if (get_user(c, user_buf)) {
+		err = -EFAULT;
+		goto done;
+	}
+
+	if (c == 'c') {
+		struct seq_file *seqf = file->private_data;
+		struct kvm_vcpu *vcpu = seqf->private;
+		/* Write does not affect our buffers previously generated with
+		 * show. seq_file is locked here to prevent races of init with
+		 * a show call */
+		mutex_lock(&seqf->lock);
+		kvmppc_init_timing_stats(vcpu);
+		mutex_unlock(&seqf->lock);
+		err = count;
+	}
+
+done:
+	return err;
+}
+
+static int kvmppc_exit_timing_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, kvmppc_exit_timing_show, inode->i_private);
+}
+
+static const struct file_operations kvmppc_exit_timing_fops = {
+	.owner   = THIS_MODULE,
+	.open    = kvmppc_exit_timing_open,
+	.read    = seq_read,
+	.write   = kvmppc_exit_timing_write,
+	.llseek  = seq_lseek,
+	.release = single_release,
+};
+
+int kvmppc_create_vcpu_debugfs_e500(struct kvm_vcpu *vcpu,
+				    struct dentry *debugfs_dentry)
+{
+	debugfs_create_file("timing", 0666, debugfs_dentry,
+			    vcpu, &kvmppc_exit_timing_fops);
+	return 0;
+}