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, 133 insertions, 0 deletions

diff --git a/lib/math/int_log.c b/lib/math/int_log.c
new file mode 100644
index 000000000..8f9da3a2a
--- /dev/null
+++ b/lib/math/int_log.c
@@ -0,0 +1,133 @@
+// SPDX-License-Identifier: LGPL-2.1-or-later
+/*
+ * Provides fixed-point logarithm operations.
+ *
+ * Copyright (C) 2006 Christoph Pfister (christophpfister@gmail.com)
+ */
+
+#include <linux/bitops.h>
+#include <linux/export.h>
+#include <linux/int_log.h>
+#include <linux/kernel.h>
+#include <linux/types.h>
+
+#include <asm/bug.h>
+
+static const unsigned short logtable[256] = {
+	0x0000, 0x0171, 0x02e0, 0x044e, 0x05ba, 0x0725, 0x088e, 0x09f7,
+	0x0b5d, 0x0cc3, 0x0e27, 0x0f8a, 0x10eb, 0x124b, 0x13aa, 0x1508,
+	0x1664, 0x17bf, 0x1919, 0x1a71, 0x1bc8, 0x1d1e, 0x1e73, 0x1fc6,
+	0x2119, 0x226a, 0x23ba, 0x2508, 0x2656, 0x27a2, 0x28ed, 0x2a37,
+	0x2b80, 0x2cc8, 0x2e0f, 0x2f54, 0x3098, 0x31dc, 0x331e, 0x345f,
+	0x359f, 0x36de, 0x381b, 0x3958, 0x3a94, 0x3bce, 0x3d08, 0x3e41,
+	0x3f78, 0x40af, 0x41e4, 0x4319, 0x444c, 0x457f, 0x46b0, 0x47e1,
+	0x4910, 0x4a3f, 0x4b6c, 0x4c99, 0x4dc5, 0x4eef, 0x5019, 0x5142,
+	0x526a, 0x5391, 0x54b7, 0x55dc, 0x5700, 0x5824, 0x5946, 0x5a68,
+	0x5b89, 0x5ca8, 0x5dc7, 0x5ee5, 0x6003, 0x611f, 0x623a, 0x6355,
+	0x646f, 0x6588, 0x66a0, 0x67b7, 0x68ce, 0x69e4, 0x6af8, 0x6c0c,
+	0x6d20, 0x6e32, 0x6f44, 0x7055, 0x7165, 0x7274, 0x7383, 0x7490,
+	0x759d, 0x76aa, 0x77b5, 0x78c0, 0x79ca, 0x7ad3, 0x7bdb, 0x7ce3,
+	0x7dea, 0x7ef0, 0x7ff6, 0x80fb, 0x81ff, 0x8302, 0x8405, 0x8507,
+	0x8608, 0x8709, 0x8809, 0x8908, 0x8a06, 0x8b04, 0x8c01, 0x8cfe,
+	0x8dfa, 0x8ef5, 0x8fef, 0x90e9, 0x91e2, 0x92db, 0x93d2, 0x94ca,
+	0x95c0, 0x96b6, 0x97ab, 0x98a0, 0x9994, 0x9a87, 0x9b7a, 0x9c6c,
+	0x9d5e, 0x9e4f, 0x9f3f, 0xa02e, 0xa11e, 0xa20c, 0xa2fa, 0xa3e7,
+	0xa4d4, 0xa5c0, 0xa6ab, 0xa796, 0xa881, 0xa96a, 0xaa53, 0xab3c,
+	0xac24, 0xad0c, 0xadf2, 0xaed9, 0xafbe, 0xb0a4, 0xb188, 0xb26c,
+	0xb350, 0xb433, 0xb515, 0xb5f7, 0xb6d9, 0xb7ba, 0xb89a, 0xb97a,
+	0xba59, 0xbb38, 0xbc16, 0xbcf4, 0xbdd1, 0xbead, 0xbf8a, 0xc065,
+	0xc140, 0xc21b, 0xc2f5, 0xc3cf, 0xc4a8, 0xc580, 0xc658, 0xc730,
+	0xc807, 0xc8de, 0xc9b4, 0xca8a, 0xcb5f, 0xcc34, 0xcd08, 0xcddc,
+	0xceaf, 0xcf82, 0xd054, 0xd126, 0xd1f7, 0xd2c8, 0xd399, 0xd469,
+	0xd538, 0xd607, 0xd6d6, 0xd7a4, 0xd872, 0xd93f, 0xda0c, 0xdad9,
+	0xdba5, 0xdc70, 0xdd3b, 0xde06, 0xded0, 0xdf9a, 0xe063, 0xe12c,
+	0xe1f5, 0xe2bd, 0xe385, 0xe44c, 0xe513, 0xe5d9, 0xe69f, 0xe765,
+	0xe82a, 0xe8ef, 0xe9b3, 0xea77, 0xeb3b, 0xebfe, 0xecc1, 0xed83,
+	0xee45, 0xef06, 0xefc8, 0xf088, 0xf149, 0xf209, 0xf2c8, 0xf387,
+	0xf446, 0xf505, 0xf5c3, 0xf680, 0xf73e, 0xf7fb, 0xf8b7, 0xf973,
+	0xfa2f, 0xfaea, 0xfba5, 0xfc60, 0xfd1a, 0xfdd4, 0xfe8e, 0xff47,
+};
+
+unsigned int intlog2(u32 value)
+{
+	/**
+	 *	returns: log2(value) * 2^24
+	 *	wrong result if value = 0 (log2(0) is undefined)
+	 */
+	unsigned int msb;
+	unsigned int logentry;
+	unsigned int significand;
+	unsigned int interpolation;
+
+	if (unlikely(value == 0)) {
+		WARN_ON(1);
+		return 0;
+	}
+
+	/* first detect the msb (count begins at 0) */
+	msb = fls(value) - 1;
+
+	/**
+	 *	now we use a logtable after the following method:
+	 *
+	 *	log2(2^x * y) * 2^24 = x * 2^24 + log2(y) * 2^24
+	 *	where x = msb and therefore 1 <= y < 2
+	 *	first y is determined by shifting the value left
+	 *	so that msb is bit 31
+	 *		0x00231f56 -> 0x8C7D5800
+	 *	the result is y * 2^31 -> "significand"
+	 *	then the highest 9 bits are used for a table lookup
+	 *	the highest bit is discarded because it's always set
+	 *	the highest nine bits in our example are 100011000
+	 *	so we would use the entry 0x18
+	 */
+	significand = value << (31 - msb);
+	logentry = (significand >> 23) % ARRAY_SIZE(logtable);
+
+	/**
+	 *	last step we do is interpolation because of the
+	 *	limitations of the log table the error is that part of
+	 *	the significand which isn't used for lookup then we
+	 *	compute the ratio between the error and the next table entry
+	 *	and interpolate it between the log table entry used and the
+	 *	next one the biggest error possible is 0x7fffff
+	 *	(in our example it's 0x7D5800)
+	 *	needed value for next table entry is 0x800000
+	 *	so the interpolation is
+	 *	(error / 0x800000) * (logtable_next - logtable_current)
+	 *	in the implementation the division is moved to the end for
+	 *	better accuracy there is also an overflow correction if
+	 *	logtable_next is 256
+	 */
+	interpolation = ((significand & 0x7fffff) *
+			((logtable[(logentry + 1) % ARRAY_SIZE(logtable)] -
+			  logtable[logentry]) & 0xffff)) >> 15;
+
+	/* now we return the result */
+	return ((msb << 24) + (logtable[logentry] << 8) + interpolation);
+}
+EXPORT_SYMBOL(intlog2);
+
+unsigned int intlog10(u32 value)
+{
+	/**
+	 *	returns: log10(value) * 2^24
+	 *	wrong result if value = 0 (log10(0) is undefined)
+	 */
+	u64 log;
+
+	if (unlikely(value == 0)) {
+		WARN_ON(1);
+		return 0;
+	}
+
+	log = intlog2(value);
+
+	/**
+	 *	we use the following method:
+	 *	log10(x) = log2(x) * log10(2)
+	 */
+
+	return (log * 646456993) >> 31;
+}
+EXPORT_SYMBOL(intlog10);