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, 287 insertions, 0 deletions

diff --git a/drivers/md/bcache/util.c b/drivers/md/bcache/util.c
new file mode 100644
index 000000000..410d8cb49
--- /dev/null
+++ b/drivers/md/bcache/util.c
@@ -0,0 +1,287 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * random utility code, for bcache but in theory not specific to bcache
+ *
+ * Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
+ * Copyright 2012 Google, Inc.
+ */
+
+#include <linux/bio.h>
+#include <linux/blkdev.h>
+#include <linux/ctype.h>
+#include <linux/debugfs.h>
+#include <linux/module.h>
+#include <linux/seq_file.h>
+#include <linux/types.h>
+#include <linux/sched/clock.h>
+
+#include "util.h"
+
+#define simple_strtoint(c, end, base)	simple_strtol(c, end, base)
+#define simple_strtouint(c, end, base)	simple_strtoul(c, end, base)
+
+#define STRTO_H(name, type)					\
+int bch_ ## name ## _h(const char *cp, type *res)		\
+{								\
+	int u = 0;						\
+	char *e;						\
+	type i = simple_ ## name(cp, &e, 10);			\
+								\
+	switch (tolower(*e)) {					\
+	default:						\
+		return -EINVAL;					\
+	case 'y':						\
+	case 'z':						\
+		u++;						\
+		fallthrough;					\
+	case 'e':						\
+		u++;						\
+		fallthrough;					\
+	case 'p':						\
+		u++;						\
+		fallthrough;					\
+	case 't':						\
+		u++;						\
+		fallthrough;					\
+	case 'g':						\
+		u++;						\
+		fallthrough;					\
+	case 'm':						\
+		u++;						\
+		fallthrough;					\
+	case 'k':						\
+		u++;						\
+		if (e++ == cp)					\
+			return -EINVAL;				\
+		fallthrough;					\
+	case '\n':						\
+	case '\0':						\
+		if (*e == '\n')					\
+			e++;					\
+	}							\
+								\
+	if (*e)							\
+		return -EINVAL;					\
+								\
+	while (u--) {						\
+		if ((type) ~0 > 0 &&				\
+		    (type) ~0 / 1024 <= i)			\
+			return -EINVAL;				\
+		if ((i > 0 && ANYSINT_MAX(type) / 1024 < i) ||	\
+		    (i < 0 && -ANYSINT_MAX(type) / 1024 > i))	\
+			return -EINVAL;				\
+		i *= 1024;					\
+	}							\
+								\
+	*res = i;						\
+	return 0;						\
+}								\
+
+STRTO_H(strtoint, int)
+STRTO_H(strtouint, unsigned int)
+STRTO_H(strtoll, long long)
+STRTO_H(strtoull, unsigned long long)
+
+/**
+ * bch_hprint - formats @v to human readable string for sysfs.
+ * @buf: the (at least 8 byte) buffer to format the result into.
+ * @v: signed 64 bit integer
+ *
+ * Returns the number of bytes used by format.
+ */
+ssize_t bch_hprint(char *buf, int64_t v)
+{
+	static const char units[] = "?kMGTPEZY";
+	int u = 0, t;
+
+	uint64_t q;
+
+	if (v < 0)
+		q = -v;
+	else
+		q = v;
+
+	/* For as long as the number is more than 3 digits, but at least
+	 * once, shift right / divide by 1024.  Keep the remainder for
+	 * a digit after the decimal point.
+	 */
+	do {
+		u++;
+
+		t = q & ~(~0 << 10);
+		q >>= 10;
+	} while (q >= 1000);
+
+	if (v < 0)
+		/* '-', up to 3 digits, '.', 1 digit, 1 character, null;
+		 * yields 8 bytes.
+		 */
+		return sprintf(buf, "-%llu.%i%c", q, t * 10 / 1024, units[u]);
+	else
+		return sprintf(buf, "%llu.%i%c", q, t * 10 / 1024, units[u]);
+}
+
+bool bch_is_zero(const char *p, size_t n)
+{
+	size_t i;
+
+	for (i = 0; i < n; i++)
+		if (p[i])
+			return false;
+	return true;
+}
+
+int bch_parse_uuid(const char *s, char *uuid)
+{
+	size_t i, j, x;
+
+	memset(uuid, 0, 16);
+
+	for (i = 0, j = 0;
+	     i < strspn(s, "-0123456789:ABCDEFabcdef") && j < 32;
+	     i++) {
+		x = s[i] | 32;
+
+		switch (x) {
+		case '0'...'9':
+			x -= '0';
+			break;
+		case 'a'...'f':
+			x -= 'a' - 10;
+			break;
+		default:
+			continue;
+		}
+
+		if (!(j & 1))
+			x <<= 4;
+		uuid[j++ >> 1] |= x;
+	}
+	return i;
+}
+
+void bch_time_stats_update(struct time_stats *stats, uint64_t start_time)
+{
+	uint64_t now, duration, last;
+
+	spin_lock(&stats->lock);
+
+	now		= local_clock();
+	duration	= time_after64(now, start_time)
+		? now - start_time : 0;
+	last		= time_after64(now, stats->last)
+		? now - stats->last : 0;
+
+	stats->max_duration = max(stats->max_duration, duration);
+
+	if (stats->last) {
+		ewma_add(stats->average_duration, duration, 8, 8);
+
+		if (stats->average_frequency)
+			ewma_add(stats->average_frequency, last, 8, 8);
+		else
+			stats->average_frequency  = last << 8;
+	} else {
+		stats->average_duration  = duration << 8;
+	}
+
+	stats->last = now ?: 1;
+
+	spin_unlock(&stats->lock);
+}
+
+/**
+ * bch_next_delay() - update ratelimiting statistics and calculate next delay
+ * @d: the struct bch_ratelimit to update
+ * @done: the amount of work done, in arbitrary units
+ *
+ * Increment @d by the amount of work done, and return how long to delay in
+ * jiffies until the next time to do some work.
+ */
+uint64_t bch_next_delay(struct bch_ratelimit *d, uint64_t done)
+{
+	uint64_t now = local_clock();
+
+	d->next += div_u64(done * NSEC_PER_SEC, atomic_long_read(&d->rate));
+
+	/* Bound the time.  Don't let us fall further than 2 seconds behind
+	 * (this prevents unnecessary backlog that would make it impossible
+	 * to catch up).  If we're ahead of the desired writeback rate,
+	 * don't let us sleep more than 2.5 seconds (so we can notice/respond
+	 * if the control system tells us to speed up!).
+	 */
+	if (time_before64(now + NSEC_PER_SEC * 5LLU / 2LLU, d->next))
+		d->next = now + NSEC_PER_SEC * 5LLU / 2LLU;
+
+	if (time_after64(now - NSEC_PER_SEC * 2, d->next))
+		d->next = now - NSEC_PER_SEC * 2;
+
+	return time_after64(d->next, now)
+		? div_u64(d->next - now, NSEC_PER_SEC / HZ)
+		: 0;
+}
+
+/*
+ * Generally it isn't good to access .bi_io_vec and .bi_vcnt directly,
+ * the preferred way is bio_add_page, but in this case, bch_bio_map()
+ * supposes that the bvec table is empty, so it is safe to access
+ * .bi_vcnt & .bi_io_vec in this way even after multipage bvec is
+ * supported.
+ */
+void bch_bio_map(struct bio *bio, void *base)
+{
+	size_t size = bio->bi_iter.bi_size;
+	struct bio_vec *bv = bio->bi_io_vec;
+
+	BUG_ON(!bio->bi_iter.bi_size);
+	BUG_ON(bio->bi_vcnt);
+
+	bv->bv_offset = base ? offset_in_page(base) : 0;
+	goto start;
+
+	for (; size; bio->bi_vcnt++, bv++) {
+		bv->bv_offset	= 0;
+start:		bv->bv_len	= min_t(size_t, PAGE_SIZE - bv->bv_offset,
+					size);
+		if (base) {
+			bv->bv_page = is_vmalloc_addr(base)
+				? vmalloc_to_page(base)
+				: virt_to_page(base);
+
+			base += bv->bv_len;
+		}
+
+		size -= bv->bv_len;
+	}
+}
+
+/**
+ * bch_bio_alloc_pages - allocates a single page for each bvec in a bio
+ * @bio: bio to allocate pages for
+ * @gfp_mask: flags for allocation
+ *
+ * Allocates pages up to @bio->bi_vcnt.
+ *
+ * Returns 0 on success, -ENOMEM on failure. On failure, any allocated pages are
+ * freed.
+ */
+int bch_bio_alloc_pages(struct bio *bio, gfp_t gfp_mask)
+{
+	int i;
+	struct bio_vec *bv;
+
+	/*
+	 * This is called on freshly new bio, so it is safe to access the
+	 * bvec table directly.
+	 */
+	for (i = 0, bv = bio->bi_io_vec; i < bio->bi_vcnt; bv++, i++) {
+		bv->bv_page = alloc_page(gfp_mask);
+		if (!bv->bv_page) {
+			while (--bv >= bio->bi_io_vec)
+				__free_page(bv->bv_page);
+			return -ENOMEM;
+		}
+	}
+
+	return 0;
+}