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, 346 insertions, 0 deletions

diff --git a/tools/include/nolibc/string.h b/tools/include/nolibc/string.h
new file mode 100644
index 000000000..4000926f4
--- /dev/null
+++ b/tools/include/nolibc/string.h
@@ -0,0 +1,346 @@
+/* SPDX-License-Identifier: LGPL-2.1 OR MIT */
+/*
+ * string function definitions for NOLIBC
+ * Copyright (C) 2017-2021 Willy Tarreau <w@1wt.eu>
+ */
+
+/* make sure to include all global symbols */
+#include "nolibc.h"
+
+#ifndef _NOLIBC_STRING_H
+#define _NOLIBC_STRING_H
+
+#include "arch.h"
+#include "std.h"
+
+static void *malloc(size_t len);
+
+/*
+ * As much as possible, please keep functions alphabetically sorted.
+ */
+
+static __attribute__((unused))
+int memcmp(const void *s1, const void *s2, size_t n)
+{
+	size_t ofs = 0;
+	int c1 = 0;
+
+	while (ofs < n && !(c1 = ((unsigned char *)s1)[ofs] - ((unsigned char *)s2)[ofs])) {
+		ofs++;
+	}
+	return c1;
+}
+
+#ifndef NOLIBC_ARCH_HAS_MEMMOVE
+/* might be ignored by the compiler without -ffreestanding, then found as
+ * missing.
+ */
+void *memmove(void *dst, const void *src, size_t len);
+__attribute__((weak,unused,section(".text.nolibc_memmove")))
+void *memmove(void *dst, const void *src, size_t len)
+{
+	size_t dir, pos;
+
+	pos = len;
+	dir = -1;
+
+	if (dst < src) {
+		pos = -1;
+		dir = 1;
+	}
+
+	while (len) {
+		pos += dir;
+		((char *)dst)[pos] = ((const char *)src)[pos];
+		len--;
+	}
+	return dst;
+}
+#endif /* #ifndef NOLIBC_ARCH_HAS_MEMMOVE */
+
+#ifndef NOLIBC_ARCH_HAS_MEMCPY
+/* must be exported, as it's used by libgcc on ARM */
+void *memcpy(void *dst, const void *src, size_t len);
+__attribute__((weak,unused,section(".text.nolibc_memcpy")))
+void *memcpy(void *dst, const void *src, size_t len)
+{
+	size_t pos = 0;
+
+	while (pos < len) {
+		((char *)dst)[pos] = ((const char *)src)[pos];
+		pos++;
+	}
+	return dst;
+}
+#endif /* #ifndef NOLIBC_ARCH_HAS_MEMCPY */
+
+#ifndef NOLIBC_ARCH_HAS_MEMSET
+/* might be ignored by the compiler without -ffreestanding, then found as
+ * missing.
+ */
+void *memset(void *dst, int b, size_t len);
+__attribute__((weak,unused,section(".text.nolibc_memset")))
+void *memset(void *dst, int b, size_t len)
+{
+	char *p = dst;
+
+	while (len--) {
+		/* prevent gcc from recognizing memset() here */
+		__asm__ volatile("");
+		*(p++) = b;
+	}
+	return dst;
+}
+#endif /* #ifndef NOLIBC_ARCH_HAS_MEMSET */
+
+#ifndef NOLIBC_ARCH_HAS_MEMCHR
+static __attribute__((unused))
+void *memchr(const void *s, int c, size_t len)
+{
+	char *p = (char *)s;
+
+	while (len--) {
+		if (*p == (char)c)
+			return p;
+		p++;
+	}
+	return NULL;
+}
+#endif /* #ifndef NOLIBC_ARCH_HAS_MEMCHR */
+
+static __attribute__((unused))
+char *strchr(const char *s, int c)
+{
+	while (*s) {
+		if (*s == (char)c)
+			return (char *)s;
+		s++;
+	}
+	return NULL;
+}
+
+static __attribute__((unused))
+int strcmp(const char *a, const char *b)
+{
+	unsigned int c;
+	int diff;
+
+	while (!(diff = (unsigned char)*a++ - (c = (unsigned char)*b++)) && c)
+		;
+	return diff;
+}
+
+static __attribute__((unused))
+char *strcpy(char *dst, const char *src)
+{
+	char *ret = dst;
+
+	while ((*dst++ = *src++));
+	return ret;
+}
+
+/* this function is only used with arguments that are not constants or when
+ * it's not known because optimizations are disabled. Note that gcc 12
+ * recognizes an strlen() pattern and replaces it with a jump to strlen(),
+ * thus itself, hence the asm() statement below that's meant to disable this
+ * confusing practice.
+ */
+size_t strlen(const char *str);
+__attribute__((weak,unused,section(".text.nolibc_strlen")))
+size_t strlen(const char *str)
+{
+	size_t len;
+
+	for (len = 0; str[len]; len++)
+		__asm__("");
+	return len;
+}
+
+/* do not trust __builtin_constant_p() at -O0, as clang will emit a test and
+ * the two branches, then will rely on an external definition of strlen().
+ */
+#if defined(__OPTIMIZE__)
+#define nolibc_strlen(x) strlen(x)
+#define strlen(str) ({                          \
+	__builtin_constant_p((str)) ?           \
+		__builtin_strlen((str)) :       \
+		nolibc_strlen((str));           \
+})
+#endif
+
+static __attribute__((unused))
+size_t strnlen(const char *str, size_t maxlen)
+{
+	size_t len;
+
+	for (len = 0; (len < maxlen) && str[len]; len++);
+	return len;
+}
+
+static __attribute__((unused))
+char *strdup(const char *str)
+{
+	size_t len;
+	char *ret;
+
+	len = strlen(str);
+	ret = malloc(len + 1);
+	if (__builtin_expect(ret != NULL, 1))
+		memcpy(ret, str, len + 1);
+
+	return ret;
+}
+
+static __attribute__((unused))
+char *strndup(const char *str, size_t maxlen)
+{
+	size_t len;
+	char *ret;
+
+	len = strnlen(str, maxlen);
+	ret = malloc(len + 1);
+	if (__builtin_expect(ret != NULL, 1)) {
+		memcpy(ret, str, len);
+		ret[len] = '\0';
+	}
+
+	return ret;
+}
+
+static __attribute__((unused))
+size_t strlcat(char *dst, const char *src, size_t size)
+{
+	size_t len = strnlen(dst, size);
+
+	/*
+	 * We want len < size-1. But as size is unsigned and can wrap
+	 * around, we use len + 1 instead.
+	 */
+	while (len + 1 < size) {
+		dst[len] = *src;
+		if (*src == '\0')
+			break;
+		len++;
+		src++;
+	}
+
+	if (len < size)
+		dst[len] = '\0';
+
+	while (*src++)
+		len++;
+
+	return len;
+}
+
+static __attribute__((unused))
+size_t strlcpy(char *dst, const char *src, size_t size)
+{
+	size_t len;
+
+	for (len = 0; len < size; len++) {
+		dst[len] = src[len];
+		if (!dst[len])
+			return len;
+	}
+	if (size)
+		dst[size-1] = '\0';
+
+	while (src[len])
+		len++;
+
+	return len;
+}
+
+static __attribute__((unused))
+char *strncat(char *dst, const char *src, size_t size)
+{
+	char *orig = dst;
+
+	while (*dst)
+		dst++;
+
+	while (size && (*dst = *src)) {
+		src++;
+		dst++;
+		size--;
+	}
+
+	*dst = 0;
+	return orig;
+}
+
+static __attribute__((unused))
+int strncmp(const char *a, const char *b, size_t size)
+{
+	unsigned int c;
+	int diff = 0;
+
+	while (size-- &&
+	       !(diff = (unsigned char)*a++ - (c = (unsigned char)*b++)) && c)
+		;
+
+	return diff;
+}
+
+static __attribute__((unused))
+char *strncpy(char *dst, const char *src, size_t size)
+{
+	size_t len;
+
+	for (len = 0; len < size; len++)
+		if ((dst[len] = *src))
+			src++;
+	return dst;
+}
+
+static __attribute__((unused))
+char *strrchr(const char *s, int c)
+{
+	const char *ret = NULL;
+
+	while (*s) {
+		if (*s == (char)c)
+			ret = s;
+		s++;
+	}
+	return (char *)ret;
+}
+
+static __attribute__((unused))
+char *strstr(const char *haystack, const char *needle)
+{
+	size_t len_haystack, len_needle;
+
+	len_needle = strlen(needle);
+	if (!len_needle)
+		return NULL;
+
+	len_haystack = strlen(haystack);
+	while (len_haystack >= len_needle) {
+		if (!memcmp(haystack, needle, len_needle))
+			return (char *)haystack;
+		haystack++;
+		len_haystack--;
+	}
+
+	return NULL;
+}
+
+static __attribute__((unused))
+int tolower(int c)
+{
+	if (c >= 'A' && c <= 'Z')
+		return c - 'A' + 'a';
+	return c;
+}
+
+static __attribute__((unused))
+int toupper(int c)
+{
+	if (c >= 'a' && c <= 'z')
+		return c - 'a' + 'A';
+	return c;
+}
+
+#endif /* _NOLIBC_STRING_H */