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, 72 insertions, 0 deletions

diff --git a/arch/powerpc/boot/ps3-head.S b/arch/powerpc/boot/ps3-head.S
new file mode 100644
index 000000000..0a4ebfcc3
--- /dev/null
+++ b/arch/powerpc/boot/ps3-head.S
@@ -0,0 +1,72 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ *  PS3 bootwrapper entry.
+ *
+ *  Copyright (C) 2007 Sony Computer Entertainment Inc.
+ *  Copyright 2007 Sony Corp.
+ */
+
+#include "ppc_asm.h"
+
+	.machine "ppc64"
+
+	.text
+
+/*
+ * __system_reset_overlay - The PS3 first stage entry.
+ *
+ * The bootwraper build script copies the 512 bytes at symbol
+ * __system_reset_overlay to offset 0x100 of the rom image.  This symbol
+ * must occupy 512 or less bytes.
+ *
+ * The PS3 has a single processor with two threads.
+ */
+
+	.globl __system_reset_overlay
+__system_reset_overlay:
+
+	/* Switch to 32-bit mode. */
+
+	mfmsr	r9
+	clrldi	r9,r9,1
+	mtmsrd	r9
+	nop
+
+	/* Get thread number in r3 and branch. */
+
+	mfspr	r3, 0x88
+	cntlzw.	r3, r3
+	beq	1f
+
+	/* Secondary goes to __secondary_hold in kernel. */
+
+	li	r4, 0x60
+	mtctr	r4
+	bctr
+
+1:
+	/* Primary delays then goes to _zimage_start in wrapper. */
+
+	or	31, 31, 31 /* db16cyc */
+	or	31, 31, 31 /* db16cyc */
+
+	lis	r4, _zimage_start@ha
+	addi	r4, r4, _zimage_start@l
+	mtctr	r4
+	bctr
+
+	. = __system_reset_overlay + 512
+
+/*
+ * __system_reset_kernel - Place holder for the kernel reset vector.
+ *
+ * The bootwrapper build script copies 512 bytes from offset 0x100
+ * of the rom image to the symbol __system_reset_kernel.  At runtime
+ * the bootwrapper program copies the 512 bytes at __system_reset_kernel
+ * to ram address 0x100.  This symbol must occupy 512 bytes.
+ */
+
+	.globl __system_reset_kernel
+__system_reset_kernel:
+
+	. = __system_reset_kernel + 512