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, 285 insertions, 0 deletions

diff --git a/lib/cmdline.c b/lib/cmdline.c
new file mode 100644
index 000000000..16cce6621
--- /dev/null
+++ b/lib/cmdline.c
@@ -0,0 +1,285 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * linux/lib/cmdline.c
+ * Helper functions generally used for parsing kernel command line
+ * and module options.
+ *
+ * Code and copyrights come from init/main.c and arch/i386/kernel/setup.c.
+ *
+ * GNU Indent formatting options for this file: -kr -i8 -npsl -pcs
+ */
+
+#include <linux/export.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/ctype.h>
+
+/*
+ *	If a hyphen was found in get_option, this will handle the
+ *	range of numbers, M-N.  This will expand the range and insert
+ *	the values[M, M+1, ..., N] into the ints array in get_options.
+ */
+
+static int get_range(char **str, int *pint, int n)
+{
+	int x, inc_counter, upper_range;
+
+	(*str)++;
+	upper_range = simple_strtol((*str), NULL, 0);
+	inc_counter = upper_range - *pint;
+	for (x = *pint; n && x < upper_range; x++, n--)
+		*pint++ = x;
+	return inc_counter;
+}
+
+/**
+ *	get_option - Parse integer from an option string
+ *	@str: option string
+ *	@pint: (optional output) integer value parsed from @str
+ *
+ *	Read an int from an option string; if available accept a subsequent
+ *	comma as well.
+ *
+ *	When @pint is NULL the function can be used as a validator of
+ *	the current option in the string.
+ *
+ *	Return:
+ *	0 - no int in string
+ *	1 - int found, no subsequent comma
+ *	2 - int found including a subsequent comma
+ *	3 - hyphen found to denote a range
+ *
+ *	Leading hyphen without integer is no integer case, but we consume it
+ *	for the sake of simplification.
+ */
+
+int get_option(char **str, int *pint)
+{
+	char *cur = *str;
+	int value;
+
+	if (!cur || !(*cur))
+		return 0;
+	if (*cur == '-')
+		value = -simple_strtoull(++cur, str, 0);
+	else
+		value = simple_strtoull(cur, str, 0);
+	if (pint)
+		*pint = value;
+	if (cur == *str)
+		return 0;
+	if (**str == ',') {
+		(*str)++;
+		return 2;
+	}
+	if (**str == '-')
+		return 3;
+
+	return 1;
+}
+EXPORT_SYMBOL(get_option);
+
+/**
+ *	get_options - Parse a string into a list of integers
+ *	@str: String to be parsed
+ *	@nints: size of integer array
+ *	@ints: integer array (must have room for at least one element)
+ *
+ *	This function parses a string containing a comma-separated
+ *	list of integers, a hyphen-separated range of _positive_ integers,
+ *	or a combination of both.  The parse halts when the array is
+ *	full, or when no more numbers can be retrieved from the
+ *	string.
+ *
+ *	When @nints is 0, the function just validates the given @str and
+ *	returns the amount of parseable integers as described below.
+ *
+ *	Returns:
+ *
+ *	The first element is filled by the number of collected integers
+ *	in the range. The rest is what was parsed from the @str.
+ *
+ *	Return value is the character in the string which caused
+ *	the parse to end (typically a null terminator, if @str is
+ *	completely parseable).
+ */
+
+char *get_options(const char *str, int nints, int *ints)
+{
+	bool validate = (nints == 0);
+	int res, i = 1;
+
+	while (i < nints || validate) {
+		int *pint = validate ? ints : ints + i;
+
+		res = get_option((char **)&str, pint);
+		if (res == 0)
+			break;
+		if (res == 3) {
+			int n = validate ? 0 : nints - i;
+			int range_nums;
+
+			range_nums = get_range((char **)&str, pint, n);
+			if (range_nums < 0)
+				break;
+			/*
+			 * Decrement the result by one to leave out the
+			 * last number in the range.  The next iteration
+			 * will handle the upper number in the range
+			 */
+			i += (range_nums - 1);
+		}
+		i++;
+		if (res == 1)
+			break;
+	}
+	ints[0] = i - 1;
+	return (char *)str;
+}
+EXPORT_SYMBOL(get_options);
+
+/**
+ *	memparse - parse a string with mem suffixes into a number
+ *	@ptr: Where parse begins
+ *	@retptr: (output) Optional pointer to next char after parse completes
+ *
+ *	Parses a string into a number.  The number stored at @ptr is
+ *	potentially suffixed with K, M, G, T, P, E.
+ *
+ *	Return: The value as recognized by simple_strtoull() multiplied
+ *	by the value as specified by suffix, if any.
+ */
+
+unsigned long long memparse(const char *ptr, char **retptr)
+{
+	char *endptr;	/* local pointer to end of parsed string */
+	unsigned long long ret = simple_strtoull(ptr, &endptr, 0);
+	unsigned int shl = 0;
+
+	/* Consume valid suffix even in case of overflow. */
+	switch (*endptr) {
+	case 'E':
+	case 'e':
+		shl += 10;
+		fallthrough;
+	case 'P':
+	case 'p':
+		shl += 10;
+		fallthrough;
+	case 'T':
+	case 't':
+		shl += 10;
+		fallthrough;
+	case 'G':
+	case 'g':
+		shl += 10;
+		fallthrough;
+	case 'M':
+	case 'm':
+		shl += 10;
+		fallthrough;
+	case 'K':
+	case 'k':
+		shl += 10;
+		fallthrough;
+	default:
+		break;
+	}
+
+	if (shl && likely(ptr != endptr)) {
+		/* Have valid suffix with preceding number. */
+		if (unlikely(check_shl_overflow(ret, shl, &ret)))
+			ret = ULLONG_MAX;
+		endptr++;
+	}
+
+	if (retptr)
+		*retptr = endptr;
+
+	return ret;
+}
+EXPORT_SYMBOL(memparse);
+
+/**
+ *	parse_option_str - Parse a string and check an option is set or not
+ *	@str: String to be parsed
+ *	@option: option name
+ *
+ *	This function parses a string containing a comma-separated list of
+ *	strings like a=b,c.
+ *
+ *	Return: True if there's such option in the string or false otherwise.
+ */
+bool parse_option_str(const char *str, const char *option)
+{
+	while (*str) {
+		if (!strncmp(str, option, strlen(option))) {
+			str += strlen(option);
+			if (!*str || *str == ',')
+				return true;
+		}
+
+		while (*str && *str != ',')
+			str++;
+
+		if (*str == ',')
+			str++;
+	}
+
+	return false;
+}
+
+/*
+ * Parse a string to get a param value pair.
+ * You can use " around spaces, but can't escape ".
+ * Hyphens and underscores equivalent in parameter names.
+ */
+char *next_arg(char *args, char **param, char **val)
+{
+	unsigned int i, equals = 0;
+	int in_quote = 0, quoted = 0;
+
+	if (*args == '"') {
+		args++;
+		in_quote = 1;
+		quoted = 1;
+	}
+
+	for (i = 0; args[i]; i++) {
+		if (isspace(args[i]) && !in_quote)
+			break;
+		if (equals == 0) {
+			if (args[i] == '=')
+				equals = i;
+		}
+		if (args[i] == '"')
+			in_quote = !in_quote;
+	}
+
+	*param = args;
+	if (!equals)
+		*val = NULL;
+	else {
+		args[equals] = '\0';
+		*val = args + equals + 1;
+
+		/* Don't include quotes in value. */
+		if (**val == '"') {
+			(*val)++;
+			if (args[i-1] == '"')
+				args[i-1] = '\0';
+		}
+	}
+	if (quoted && i > 0 && args[i-1] == '"')
+		args[i-1] = '\0';
+
+	if (args[i]) {
+		args[i] = '\0';
+		args += i + 1;
+	} else
+		args += i;
+
+	/* Chew up trailing spaces. */
+	return skip_spaces(args);
+}
+EXPORT_SYMBOL(next_arg);