1 // SPDX-License-Identifier: GPL-2.0-only
2 
3 #include <linux/efi.h>
4 #include <linux/memblock.h>
5 #include <linux/spinlock.h>
6 #include <asm/unaccepted_memory.h>
7 
8 /* Protects unaccepted memory bitmap and accepting_list */
9 static DEFINE_SPINLOCK(unaccepted_memory_lock);
10 
11 struct accept_range {
12 	struct list_head list;
13 	unsigned long start;
14 	unsigned long end;
15 };
16 
17 static LIST_HEAD(accepting_list);
18 
19 /*
20  * accept_memory() -- Consult bitmap and accept the memory if needed.
21  *
22  * Only memory that is explicitly marked as unaccepted in the bitmap requires
23  * an action. All the remaining memory is implicitly accepted and doesn't need
24  * acceptance.
25  *
26  * No need to accept:
27  *  - anything if the system has no unaccepted table;
28  *  - memory that is below phys_base;
29  *  - memory that is above the memory that addressable by the bitmap;
30  */
31 void accept_memory(phys_addr_t start, phys_addr_t end)
32 {
33 	struct efi_unaccepted_memory *unaccepted;
34 	unsigned long range_start, range_end;
35 	struct accept_range range, *entry;
36 	unsigned long flags;
37 	u64 unit_size;
38 
39 	unaccepted = efi_get_unaccepted_table();
40 	if (!unaccepted)
41 		return;
42 
43 	unit_size = unaccepted->unit_size;
44 
45 	/*
46 	 * Only care for the part of the range that is represented
47 	 * in the bitmap.
48 	 */
49 	if (start < unaccepted->phys_base)
50 		start = unaccepted->phys_base;
51 	if (end < unaccepted->phys_base)
52 		return;
53 
54 	/* Translate to offsets from the beginning of the bitmap */
55 	start -= unaccepted->phys_base;
56 	end -= unaccepted->phys_base;
57 
58 	/*
59 	 * load_unaligned_zeropad() can lead to unwanted loads across page
60 	 * boundaries. The unwanted loads are typically harmless. But, they
61 	 * might be made to totally unrelated or even unmapped memory.
62 	 * load_unaligned_zeropad() relies on exception fixup (#PF, #GP and now
63 	 * #VE) to recover from these unwanted loads.
64 	 *
65 	 * But, this approach does not work for unaccepted memory. For TDX, a
66 	 * load from unaccepted memory will not lead to a recoverable exception
67 	 * within the guest. The guest will exit to the VMM where the only
68 	 * recourse is to terminate the guest.
69 	 *
70 	 * There are two parts to fix this issue and comprehensively avoid
71 	 * access to unaccepted memory. Together these ensure that an extra
72 	 * "guard" page is accepted in addition to the memory that needs to be
73 	 * used:
74 	 *
75 	 * 1. Implicitly extend the range_contains_unaccepted_memory(start, end)
76 	 *    checks up to end+unit_size if 'end' is aligned on a unit_size
77 	 *    boundary.
78 	 *
79 	 * 2. Implicitly extend accept_memory(start, end) to end+unit_size if
80 	 *    'end' is aligned on a unit_size boundary. (immediately following
81 	 *    this comment)
82 	 */
83 	if (!(end % unit_size))
84 		end += unit_size;
85 
86 	/* Make sure not to overrun the bitmap */
87 	if (end > unaccepted->size * unit_size * BITS_PER_BYTE)
88 		end = unaccepted->size * unit_size * BITS_PER_BYTE;
89 
90 	range.start = start / unit_size;
91 	range.end = DIV_ROUND_UP(end, unit_size);
92 retry:
93 	spin_lock_irqsave(&unaccepted_memory_lock, flags);
94 
95 	/*
96 	 * Check if anybody works on accepting the same range of the memory.
97 	 *
98 	 * The check is done with unit_size granularity. It is crucial to catch
99 	 * all accept requests to the same unit_size block, even if they don't
100 	 * overlap on physical address level.
101 	 */
102 	list_for_each_entry(entry, &accepting_list, list) {
103 		if (entry->end < range.start)
104 			continue;
105 		if (entry->start >= range.end)
106 			continue;
107 
108 		/*
109 		 * Somebody else accepting the range. Or at least part of it.
110 		 *
111 		 * Drop the lock and retry until it is complete.
112 		 */
113 		spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
114 		goto retry;
115 	}
116 
117 	/*
118 	 * Register that the range is about to be accepted.
119 	 * Make sure nobody else will accept it.
120 	 */
121 	list_add(&range.list, &accepting_list);
122 
123 	range_start = range.start;
124 	for_each_set_bitrange_from(range_start, range_end, unaccepted->bitmap,
125 				   range.end) {
126 		unsigned long phys_start, phys_end;
127 		unsigned long len = range_end - range_start;
128 
129 		phys_start = range_start * unit_size + unaccepted->phys_base;
130 		phys_end = range_end * unit_size + unaccepted->phys_base;
131 
132 		/*
133 		 * Keep interrupts disabled until the accept operation is
134 		 * complete in order to prevent deadlocks.
135 		 *
136 		 * Enabling interrupts before calling arch_accept_memory()
137 		 * creates an opportunity for an interrupt handler to request
138 		 * acceptance for the same memory. The handler will continuously
139 		 * spin with interrupts disabled, preventing other task from
140 		 * making progress with the acceptance process.
141 		 */
142 		spin_unlock(&unaccepted_memory_lock);
143 
144 		arch_accept_memory(phys_start, phys_end);
145 
146 		spin_lock(&unaccepted_memory_lock);
147 		bitmap_clear(unaccepted->bitmap, range_start, len);
148 	}
149 
150 	list_del(&range.list);
151 	spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
152 }
153 
154 bool range_contains_unaccepted_memory(phys_addr_t start, phys_addr_t end)
155 {
156 	struct efi_unaccepted_memory *unaccepted;
157 	unsigned long flags;
158 	bool ret = false;
159 	u64 unit_size;
160 
161 	unaccepted = efi_get_unaccepted_table();
162 	if (!unaccepted)
163 		return false;
164 
165 	unit_size = unaccepted->unit_size;
166 
167 	/*
168 	 * Only care for the part of the range that is represented
169 	 * in the bitmap.
170 	 */
171 	if (start < unaccepted->phys_base)
172 		start = unaccepted->phys_base;
173 	if (end < unaccepted->phys_base)
174 		return false;
175 
176 	/* Translate to offsets from the beginning of the bitmap */
177 	start -= unaccepted->phys_base;
178 	end -= unaccepted->phys_base;
179 
180 	/*
181 	 * Also consider the unaccepted state of the *next* page. See fix #1 in
182 	 * the comment on load_unaligned_zeropad() in accept_memory().
183 	 */
184 	if (!(end % unit_size))
185 		end += unit_size;
186 
187 	/* Make sure not to overrun the bitmap */
188 	if (end > unaccepted->size * unit_size * BITS_PER_BYTE)
189 		end = unaccepted->size * unit_size * BITS_PER_BYTE;
190 
191 	spin_lock_irqsave(&unaccepted_memory_lock, flags);
192 	while (start < end) {
193 		if (test_bit(start / unit_size, unaccepted->bitmap)) {
194 			ret = true;
195 			break;
196 		}
197 
198 		start += unit_size;
199 	}
200 	spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
201 
202 	return ret;
203 }
204