1 /*
2 * asid.c: ASID management
3 * Copyright (c) 2007, Advanced Micro Devices, Inc.
4 * Copyright (c) 2009, Citrix Systems, Inc.
5 *
6 * This program is free software; you can redistribute it and/or modify it
7 * under the terms and conditions of the GNU General Public License,
8 * version 2, as published by the Free Software Foundation.
9 *
10 * This program is distributed in the hope it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
13 * more details.
14 *
15 * You should have received a copy of the GNU General Public License along with
16 * this program; If not, see <http://www.gnu.org/licenses/>.
17 */
18
19 #include <xen/init.h>
20 #include <xen/lib.h>
21 #include <xen/sched.h>
22 #include <xen/smp.h>
23 #include <xen/percpu.h>
24 #include <asm/hvm/asid.h>
25
26 /* Xen command-line option to enable ASIDs */
27 static int opt_asid_enabled = 1;
28 boolean_param("asid", opt_asid_enabled);
29
30 /*
31 * ASIDs partition the physical TLB. In the current implementation ASIDs are
32 * introduced to reduce the number of TLB flushes. Each time the guest's
33 * virtual address space changes (e.g. due to an INVLPG, MOV-TO-{CR3, CR4}
34 * operation), instead of flushing the TLB, a new ASID is assigned. This
35 * reduces the number of TLB flushes to at most 1/#ASIDs. The biggest
36 * advantage is that hot parts of the hypervisor's code and data retain in
37 * the TLB.
38 *
39 * Sketch of the Implementation:
40 *
41 * ASIDs are a CPU-local resource. As preemption of ASIDs is not possible,
42 * ASIDs are assigned in a round-robin scheme. To minimize the overhead of
43 * ASID invalidation, at the time of a TLB flush, ASIDs are tagged with a
44 * 64-bit generation. Only on a generation overflow the code needs to
45 * invalidate all ASID information stored at the VCPUs with are run on the
46 * specific physical processor. This overflow appears after about 2^80
47 * host processor cycles, so we do not optimize this case, but simply disable
48 * ASID useage to retain correctness.
49 */
50
51 /* Per-CPU ASID management. */
52 struct hvm_asid_data {
53 uint64_t core_asid_generation;
54 uint32_t next_asid;
55 uint32_t max_asid;
56 bool_t disabled;
57 };
58
59 static DEFINE_PER_CPU(struct hvm_asid_data, hvm_asid_data);
60
hvm_asid_init(int nasids)61 void hvm_asid_init(int nasids)
62 {
63 static int8_t g_disabled = -1;
64 struct hvm_asid_data *data = &this_cpu(hvm_asid_data);
65
66 data->max_asid = nasids - 1;
67 data->disabled = !opt_asid_enabled || (nasids <= 1);
68
69 if ( g_disabled != data->disabled )
70 {
71 printk("HVM: ASIDs %sabled.\n", data->disabled ? "dis" : "en");
72 if ( g_disabled < 0 )
73 g_disabled = data->disabled;
74 }
75
76 /* Zero indicates 'invalid generation', so we start the count at one. */
77 data->core_asid_generation = 1;
78
79 /* Zero indicates 'ASIDs disabled', so we start the count at one. */
80 data->next_asid = 1;
81 }
82
hvm_asid_flush_vcpu_asid(struct hvm_vcpu_asid * asid)83 void hvm_asid_flush_vcpu_asid(struct hvm_vcpu_asid *asid)
84 {
85 asid->generation = 0;
86 }
87
hvm_asid_flush_vcpu(struct vcpu * v)88 void hvm_asid_flush_vcpu(struct vcpu *v)
89 {
90 hvm_asid_flush_vcpu_asid(&v->arch.hvm_vcpu.n1asid);
91 hvm_asid_flush_vcpu_asid(&vcpu_nestedhvm(v).nv_n2asid);
92 }
93
hvm_asid_flush_core(void)94 void hvm_asid_flush_core(void)
95 {
96 struct hvm_asid_data *data = &this_cpu(hvm_asid_data);
97
98 if ( data->disabled )
99 return;
100
101 if ( likely(++data->core_asid_generation != 0) )
102 return;
103
104 /*
105 * ASID generations are 64 bit. Overflow of generations never happens.
106 * For safety, we simply disable ASIDs, so correctness is established; it
107 * only runs a bit slower.
108 */
109 printk("HVM: ASID generation overrun. Disabling ASIDs.\n");
110 data->disabled = 1;
111 }
112
hvm_asid_handle_vmenter(struct hvm_vcpu_asid * asid)113 bool_t hvm_asid_handle_vmenter(struct hvm_vcpu_asid *asid)
114 {
115 struct hvm_asid_data *data = &this_cpu(hvm_asid_data);
116
117 /* On erratum #170 systems we must flush the TLB.
118 * Generation overruns are taken here, too. */
119 if ( data->disabled )
120 goto disabled;
121
122 /* Test if VCPU has valid ASID. */
123 if ( asid->generation == data->core_asid_generation )
124 return 0;
125
126 /* If there are no free ASIDs, need to go to a new generation */
127 if ( unlikely(data->next_asid > data->max_asid) )
128 {
129 hvm_asid_flush_core();
130 data->next_asid = 1;
131 if ( data->disabled )
132 goto disabled;
133 }
134
135 /* Now guaranteed to be a free ASID. */
136 asid->asid = data->next_asid++;
137 asid->generation = data->core_asid_generation;
138
139 /*
140 * When we assign ASID 1, flush all TLB entries as we are starting a new
141 * generation, and all old ASID allocations are now stale.
142 */
143 return (asid->asid == 1);
144
145 disabled:
146 asid->asid = 0;
147 return 0;
148 }
149
150 /*
151 * Local variables:
152 * mode: C
153 * c-file-style: "BSD"
154 * c-basic-offset: 4
155 * tab-width: 4
156 * indent-tabs-mode: nil
157 * End:
158 */
159