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, 162 insertions, 0 deletions

diff --git a/drivers/acpi/acpi_lpit.c b/drivers/acpi/acpi_lpit.c
new file mode 100644
index 000000000..b8d98b1b4
--- /dev/null
+++ b/drivers/acpi/acpi_lpit.c
@@ -0,0 +1,162 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ * acpi_lpit.c - LPIT table processing functions
+ *
+ * Copyright (C) 2017 Intel Corporation. All rights reserved.
+ */
+
+#include <linux/cpu.h>
+#include <linux/acpi.h>
+#include <asm/msr.h>
+#include <asm/tsc.h>
+#include "internal.h"
+
+struct lpit_residency_info {
+	struct acpi_generic_address gaddr;
+	u64 frequency;
+	void __iomem *iomem_addr;
+};
+
+/* Storage for an memory mapped and FFH based entries */
+static struct lpit_residency_info residency_info_mem;
+static struct lpit_residency_info residency_info_ffh;
+
+static int lpit_read_residency_counter_us(u64 *counter, bool io_mem)
+{
+	int err;
+
+	if (io_mem) {
+		u64 count = 0;
+		int error;
+
+		error = acpi_os_read_iomem(residency_info_mem.iomem_addr, &count,
+					   residency_info_mem.gaddr.bit_width);
+		if (error)
+			return error;
+
+		*counter = div64_u64(count * 1000000ULL, residency_info_mem.frequency);
+		return 0;
+	}
+
+	err = rdmsrq_safe(residency_info_ffh.gaddr.address, counter);
+	if (!err) {
+		u64 mask = GENMASK_ULL(residency_info_ffh.gaddr.bit_offset +
+				       residency_info_ffh.gaddr. bit_width - 1,
+				       residency_info_ffh.gaddr.bit_offset);
+
+		*counter &= mask;
+		*counter >>= residency_info_ffh.gaddr.bit_offset;
+		*counter = div64_u64(*counter * 1000000ULL, residency_info_ffh.frequency);
+		return 0;
+	}
+
+	return -ENODATA;
+}
+
+static ssize_t low_power_idle_system_residency_us_show(struct device *dev,
+						       struct device_attribute *attr,
+						       char *buf)
+{
+	u64 counter;
+	int ret;
+
+	ret = lpit_read_residency_counter_us(&counter, true);
+	if (ret)
+		return ret;
+
+	return sprintf(buf, "%llu\n", counter);
+}
+static DEVICE_ATTR_RO(low_power_idle_system_residency_us);
+
+static ssize_t low_power_idle_cpu_residency_us_show(struct device *dev,
+						    struct device_attribute *attr,
+						    char *buf)
+{
+	u64 counter;
+	int ret;
+
+	ret = lpit_read_residency_counter_us(&counter, false);
+	if (ret)
+		return ret;
+
+	return sprintf(buf, "%llu\n", counter);
+}
+static DEVICE_ATTR_RO(low_power_idle_cpu_residency_us);
+
+int lpit_read_residency_count_address(u64 *address)
+{
+	if (!residency_info_mem.gaddr.address)
+		return -EINVAL;
+
+	*address = residency_info_mem.gaddr.address;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(lpit_read_residency_count_address);
+
+static void lpit_update_residency(struct lpit_residency_info *info,
+				 struct acpi_lpit_native *lpit_native)
+{
+	struct device *dev_root = bus_get_dev_root(&cpu_subsys);
+
+	/* Silently fail, if cpuidle attribute group is not present */
+	if (!dev_root)
+		return;
+
+	info->frequency = lpit_native->counter_frequency ?
+				lpit_native->counter_frequency : mul_u32_u32(tsc_khz, 1000U);
+	if (!info->frequency)
+		info->frequency = 1;
+
+	info->gaddr = lpit_native->residency_counter;
+	if (info->gaddr.space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) {
+		info->iomem_addr = ioremap(info->gaddr.address,
+						   info->gaddr.bit_width / 8);
+		if (!info->iomem_addr)
+			goto exit;
+
+		sysfs_add_file_to_group(&dev_root->kobj,
+					&dev_attr_low_power_idle_system_residency_us.attr,
+					"cpuidle");
+	} else if (info->gaddr.space_id == ACPI_ADR_SPACE_FIXED_HARDWARE) {
+		sysfs_add_file_to_group(&dev_root->kobj,
+					&dev_attr_low_power_idle_cpu_residency_us.attr,
+					"cpuidle");
+	}
+exit:
+	put_device(dev_root);
+}
+
+static void lpit_process(u64 begin, u64 end)
+{
+	while (begin + sizeof(struct acpi_lpit_native) <= end) {
+		struct acpi_lpit_native *lpit_native = (struct acpi_lpit_native *)begin;
+
+		if (!lpit_native->header.type && !lpit_native->header.flags) {
+			if (lpit_native->residency_counter.space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY &&
+			    !residency_info_mem.gaddr.address) {
+				lpit_update_residency(&residency_info_mem, lpit_native);
+			} else if (lpit_native->residency_counter.space_id == ACPI_ADR_SPACE_FIXED_HARDWARE &&
+				   !residency_info_ffh.gaddr.address) {
+				lpit_update_residency(&residency_info_ffh, lpit_native);
+			}
+		}
+		begin += lpit_native->header.length;
+	}
+}
+
+void acpi_init_lpit(void)
+{
+	acpi_status status;
+	struct acpi_table_lpit *lpit;
+
+	status = acpi_get_table(ACPI_SIG_LPIT, 0, (struct acpi_table_header **)&lpit);
+	if (ACPI_FAILURE(status))
+		return;
+
+	lpit_process((u64)lpit + sizeof(*lpit),
+		     (u64)lpit + lpit->header.length);
+
+	acpi_put_table((struct acpi_table_header *)lpit);
+}