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, 90 insertions, 0 deletions

diff --git a/drivers/video/fbdev/bt455.h b/drivers/video/fbdev/bt455.h
new file mode 100644
index 000000000..dd1404b40
--- /dev/null
+++ b/drivers/video/fbdev/bt455.h
@@ -0,0 +1,90 @@
+/*
+ *	linux/drivers/video/bt455.h
+ *
+ *	Copyright 2003  Thiemo Seufer <seufer@csv.ica.uni-stuttgart.de>
+ *	Copyright 2016  Maciej W. Rozycki <macro@linux-mips.org>
+ *
+ *	This file is subject to the terms and conditions of the GNU General
+ *	Public License. See the file COPYING in the main directory of this
+ *	archive for more details.
+ */
+#include <linux/types.h>
+
+/*
+ * Bt455 byte-wide registers, 32-bit aligned.
+ */
+struct bt455_regs {
+	volatile u8 addr_cmap;
+	u8 pad0[3];
+	volatile u8 addr_cmap_data;
+	u8 pad1[3];
+	volatile u8 addr_clr;
+	u8 pad2[3];
+	volatile u8 addr_ovly;
+	u8 pad3[3];
+};
+
+static inline void bt455_select_reg(struct bt455_regs *regs, int ir)
+{
+	mb();
+	regs->addr_cmap = ir & 0x0f;
+}
+
+static inline void bt455_reset_reg(struct bt455_regs *regs)
+{
+	mb();
+	regs->addr_clr = 0;
+}
+
+/*
+ * Read/write to a Bt455 color map register.
+ */
+static inline void bt455_read_cmap_next(struct bt455_regs *regs, u8 *grey)
+{
+	mb();
+	regs->addr_cmap_data;
+	rmb();
+	*grey = regs->addr_cmap_data & 0xf;
+	rmb();
+	regs->addr_cmap_data;
+}
+
+static inline void bt455_write_cmap_next(struct bt455_regs *regs, u8 grey)
+{
+	wmb();
+	regs->addr_cmap_data = 0x0;
+	wmb();
+	regs->addr_cmap_data = grey & 0xf;
+	wmb();
+	regs->addr_cmap_data = 0x0;
+}
+
+static inline void bt455_write_ovly_next(struct bt455_regs *regs, u8 grey)
+{
+	wmb();
+	regs->addr_ovly = 0x0;
+	wmb();
+	regs->addr_ovly = grey & 0xf;
+	wmb();
+	regs->addr_ovly = 0x0;
+}
+
+static inline void bt455_read_cmap_entry(struct bt455_regs *regs,
+					 int cr, u8 *grey)
+{
+	bt455_select_reg(regs, cr);
+	bt455_read_cmap_next(regs, grey);
+}
+
+static inline void bt455_write_cmap_entry(struct bt455_regs *regs,
+					  int cr, u8 grey)
+{
+	bt455_select_reg(regs, cr);
+	bt455_write_cmap_next(regs, grey);
+}
+
+static inline void bt455_write_ovly_entry(struct bt455_regs *regs, u8 grey)
+{
+	bt455_reset_reg(regs);
+	bt455_write_ovly_next(regs, grey);
+}