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, 164 insertions, 0 deletions

diff --git a/drivers/net/pse-pd/realtek-pse-mcu-uart.c b/drivers/net/pse-pd/realtek-pse-mcu-uart.c
new file mode 100644
index 000000000..9baa17d8d
--- /dev/null
+++ b/drivers/net/pse-pd/realtek-pse-mcu-uart.c
@@ -0,0 +1,164 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/cleanup.h>
+#include <linux/completion.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/pse-pd/pse.h>
+#include <linux/serdev.h>
+#include <linux/spinlock.h>
+#include <linux/string.h>
+
+#include "realtek-pse-mcu.h"
+
+#define RTPSE_MCU_UART_BAUD_DEFAULT	19200
+#define RTPSE_MCU_UART_TX_TIMEOUT	msecs_to_jiffies(100)
+#define RTPSE_MCU_UART_RX_TIMEOUT	msecs_to_jiffies(RTPSE_MCU_RESPONSE_MAX_MS)
+
+struct rtpse_mcu_uart {
+	struct rtpse_mcu_ctrl pse;
+	struct serdev_device *serdev;
+	struct completion rx_done;
+	spinlock_t rx_lock;		/* protects rx_buf and rx_len */
+	size_t rx_len;
+	u8 rx_buf[RTPSE_MCU_MSG_SIZE];
+};
+
+#define to_rtpse_mcu_uart(p)  container_of(p, struct rtpse_mcu_uart, pse)
+
+/*
+ * No framing is done here: a glitched frame costs one transaction, then
+ * the next _send re-frames from rx_len 0. Resync works by returning count
+ * (not take), dropping any overflow so serdev keeps no leftover to bleed
+ * into the next frame.
+ */
+static size_t rtpse_mcu_uart_receive(struct serdev_device *serdev,
+				     const u8 *buf, size_t count)
+{
+	struct rtpse_mcu_uart *ctx = serdev_device_get_drvdata(serdev);
+	size_t take;
+
+	scoped_guard(spinlock_irqsave, &ctx->rx_lock) {
+		take = min(count, sizeof(ctx->rx_buf) - ctx->rx_len);
+		if (take) {
+			memcpy(ctx->rx_buf + ctx->rx_len, buf, take);
+			ctx->rx_len += take;
+			if (ctx->rx_len == sizeof(ctx->rx_buf))
+				complete(&ctx->rx_done);
+		}
+	}
+
+	/* consume all to avoid desync/misalignment */
+	return count;
+}
+
+static const struct serdev_device_ops rtpse_mcu_uart_serdev_ops = {
+	.receive_buf = rtpse_mcu_uart_receive,
+	.write_wakeup = serdev_device_write_wakeup,
+};
+
+static int rtpse_mcu_uart_send(struct rtpse_mcu_ctrl *pse, const struct rtpse_mcu_msg *req)
+{
+	struct rtpse_mcu_uart *ctx = to_rtpse_mcu_uart(pse);
+	int written;
+
+	/* clear any leftover rx state before transmitting */
+	scoped_guard(spinlock_irqsave, &ctx->rx_lock) {
+		reinit_completion(&ctx->rx_done);
+		ctx->rx_len = 0;
+	}
+
+	written = serdev_device_write(ctx->serdev, (const u8 *)req, sizeof(*req),
+				      RTPSE_MCU_UART_TX_TIMEOUT);
+	if (written < 0)
+		return written;
+	if (written != sizeof(*req))
+		return -EIO;
+
+	return 0;
+}
+
+static int rtpse_mcu_uart_recv(struct rtpse_mcu_ctrl *pse,
+			       const struct rtpse_mcu_msg *req,
+			       struct rtpse_mcu_msg *resp)
+{
+	struct rtpse_mcu_uart *ctx = to_rtpse_mcu_uart(pse);
+
+	if (!wait_for_completion_timeout(&ctx->rx_done, RTPSE_MCU_UART_RX_TIMEOUT))
+		return -ETIMEDOUT;
+
+	scoped_guard(spinlock_irqsave, &ctx->rx_lock) {
+		if (ctx->rx_len != sizeof(*resp))
+			return -EIO;
+
+		memcpy(resp, ctx->rx_buf, sizeof(*resp));
+	}
+	return 0;
+}
+
+static const struct rtpse_mcu_transport_ops rtpse_mcu_uart_transport_ops = {
+	.send = rtpse_mcu_uart_send,
+	.recv = rtpse_mcu_uart_recv,
+};
+
+static int rtpse_mcu_uart_probe(struct serdev_device *serdev)
+{
+	u32 speed = RTPSE_MCU_UART_BAUD_DEFAULT;
+	struct device *dev = &serdev->dev;
+	struct rtpse_mcu_uart *ctx;
+	unsigned int baud;
+	int ret;
+
+	ctx = devm_kzalloc(dev, sizeof(*ctx), GFP_KERNEL);
+	if (!ctx)
+		return -ENOMEM;
+
+	ctx->serdev = serdev;
+	ctx->pse.dev = dev;
+	ctx->pse.pcdev.owner = THIS_MODULE;
+	ctx->pse.transport = &rtpse_mcu_uart_transport_ops;
+	init_completion(&ctx->rx_done);
+	spin_lock_init(&ctx->rx_lock);
+
+	serdev_device_set_drvdata(serdev, ctx);
+	serdev_device_set_client_ops(serdev, &rtpse_mcu_uart_serdev_ops);
+
+	ret = devm_serdev_device_open(dev, serdev);
+	if (ret)
+		return dev_err_probe(dev, ret, "failed to open serdev\n");
+
+	fwnode_property_read_u32(dev_fwnode(dev), "current-speed", &speed);
+
+	baud = serdev_device_set_baudrate(serdev, speed);
+	if (baud != speed)
+		dev_warn(dev, "could not set baudrate %u, controller uses %u\n",
+			 speed, baud);
+
+	serdev_device_set_flow_control(serdev, false);
+
+	ret = serdev_device_set_parity(serdev, SERDEV_PARITY_NONE);
+	if (ret)
+		dev_warn(dev, "could not set parity to none: %d\n", ret);
+
+	return rtpse_mcu_register(&ctx->pse);
+}
+
+static const struct of_device_id rtpse_mcu_uart_of_match[] = {
+	{ .compatible = "realtek,pse-mcu-gen1", .data = &rtpse_mcu_gen1_data },
+	{ .compatible = "realtek,pse-mcu-gen2", .data = &rtpse_mcu_gen2_data },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, rtpse_mcu_uart_of_match);
+
+static struct serdev_device_driver rtpse_mcu_uart_driver = {
+	.driver = {
+		.name = "realtek-pse-mcu-uart",
+		.of_match_table = rtpse_mcu_uart_of_match,
+	},
+	.probe  = rtpse_mcu_uart_probe,
+};
+module_serdev_device_driver(rtpse_mcu_uart_driver);
+
+MODULE_AUTHOR("Jonas Jelonek <jelonek.jonas@gmail.com>");
+MODULE_DESCRIPTION("Realtek PSE MCU driver (UART transport)");
+MODULE_LICENSE("GPL");