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, 130 insertions, 0 deletions

diff --git a/drivers/net/phy/ax88796b.c b/drivers/net/phy/ax88796b.c
new file mode 100644
index 000000000..f20ddf649
--- /dev/null
+++ b/drivers/net/phy/ax88796b.c
@@ -0,0 +1,130 @@
+// SPDX-License-Identifier: GPL-2.0+
+/* Driver for Asix PHYs
+ *
+ * Author: Michael Schmitz <schmitzmic@gmail.com>
+ */
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/mii.h>
+#include <linux/phy.h>
+
+#define PHY_ID_ASIX_AX88772A		0x003b1861
+#define PHY_ID_ASIX_AX88772C		0x003b1881
+#define PHY_ID_ASIX_AX88796B		0x003b1841
+
+MODULE_DESCRIPTION("Asix PHY driver");
+MODULE_AUTHOR("Michael Schmitz <schmitzmic@gmail.com>");
+MODULE_LICENSE("GPL");
+
+/**
+ * asix_soft_reset - software reset the PHY via BMCR_RESET bit
+ * @phydev: target phy_device struct
+ *
+ * Description: Perform a software PHY reset using the standard
+ * BMCR_RESET bit and poll for the reset bit to be cleared.
+ * Toggle BMCR_RESET bit off to accommodate broken AX8796B PHY implementation
+ * such as used on the Individual Computers' X-Surf 100 Zorro card.
+ *
+ * Returns: 0 on success, < 0 on failure
+ */
+static int asix_soft_reset(struct phy_device *phydev)
+{
+	int ret;
+
+	/* Asix PHY won't reset unless reset bit toggles */
+	ret = phy_write(phydev, MII_BMCR, 0);
+	if (ret < 0)
+		return ret;
+
+	return genphy_soft_reset(phydev);
+}
+
+/* AX88772A is not working properly with some old switches (NETGEAR EN 108TP):
+ * after autoneg is done and the link status is reported as active, the MII_LPA
+ * register is 0. This issue is not reproducible on AX88772C.
+ */
+static int asix_ax88772a_read_status(struct phy_device *phydev)
+{
+	int ret, val;
+
+	ret = genphy_update_link(phydev);
+	if (ret)
+		return ret;
+
+	if (!phydev->link)
+		return 0;
+
+	/* If MII_LPA is 0, phy_resolve_aneg_linkmode() will fail to resolve
+	 * linkmode so use MII_BMCR as default values.
+	 */
+	val = phy_read(phydev, MII_BMCR);
+	if (val < 0)
+		return val;
+
+	if (val & BMCR_SPEED100)
+		phydev->speed = SPEED_100;
+	else
+		phydev->speed = SPEED_10;
+
+	if (val & BMCR_FULLDPLX)
+		phydev->duplex = DUPLEX_FULL;
+	else
+		phydev->duplex = DUPLEX_HALF;
+
+	ret = genphy_read_lpa(phydev);
+	if (ret < 0)
+		return ret;
+
+	if (phydev->autoneg == AUTONEG_ENABLE && phydev->autoneg_complete)
+		phy_resolve_aneg_linkmode(phydev);
+
+	return 0;
+}
+
+static void asix_ax88772a_link_change_notify(struct phy_device *phydev)
+{
+	/* Reset PHY, otherwise MII_LPA will provide outdated information.
+	 * This issue is reproducible only with some link partner PHYs
+	 */
+	if (phydev->state == PHY_NOLINK) {
+		phy_init_hw(phydev);
+		_phy_start_aneg(phydev);
+	}
+}
+
+static struct phy_driver asix_driver[] = {
+{
+	PHY_ID_MATCH_EXACT(PHY_ID_ASIX_AX88772A),
+	.name		= "Asix Electronics AX88772A",
+	.flags		= PHY_IS_INTERNAL,
+	.read_status	= asix_ax88772a_read_status,
+	.suspend	= genphy_suspend,
+	.resume		= genphy_resume,
+	.soft_reset	= asix_soft_reset,
+	.link_change_notify	= asix_ax88772a_link_change_notify,
+}, {
+	PHY_ID_MATCH_EXACT(PHY_ID_ASIX_AX88772C),
+	.name		= "Asix Electronics AX88772C",
+	.flags		= PHY_IS_INTERNAL,
+	.suspend	= genphy_suspend,
+	.resume		= genphy_resume,
+	.soft_reset	= asix_soft_reset,
+}, {
+	PHY_ID_MATCH_MODEL(PHY_ID_ASIX_AX88796B),
+	.name		= "Asix Electronics AX88796B",
+	/* PHY_BASIC_FEATURES */
+	.soft_reset	= asix_soft_reset,
+} };
+
+module_phy_driver(asix_driver);
+
+static const struct mdio_device_id __maybe_unused asix_tbl[] = {
+	{ PHY_ID_MATCH_EXACT(PHY_ID_ASIX_AX88772A) },
+	{ PHY_ID_MATCH_EXACT(PHY_ID_ASIX_AX88772C) },
+	{ PHY_ID_MATCH_MODEL(PHY_ID_ASIX_AX88796B) },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(mdio, asix_tbl);