1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * arch/arm64/kvm/fpsimd.c: Guest/host FPSIMD context coordination helpers
4 *
5 * Copyright 2018 Arm Limited
6 * Author: Dave Martin <[email protected]>
7 */
8 #include <linux/irqflags.h>
9 #include <linux/sched.h>
10 #include <linux/kvm_host.h>
11 #include <asm/fpsimd.h>
12 #include <asm/kvm_asm.h>
13 #include <asm/kvm_hyp.h>
14 #include <asm/kvm_mmu.h>
15 #include <asm/sysreg.h>
16
17 /*
18 * Called on entry to KVM_RUN unless this vcpu previously ran at least
19 * once and the most recent prior KVM_RUN for this vcpu was called from
20 * the same task as current (highly likely).
21 *
22 * This is guaranteed to execute before kvm_arch_vcpu_load_fp(vcpu),
23 * such that on entering hyp the relevant parts of current are already
24 * mapped.
25 */
kvm_arch_vcpu_run_map_fp(struct kvm_vcpu * vcpu)26 int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu)
27 {
28 struct user_fpsimd_state *fpsimd = ¤t->thread.uw.fpsimd_state;
29 int ret;
30
31 /* pKVM has its own tracking of the host fpsimd state. */
32 if (is_protected_kvm_enabled())
33 return 0;
34
35 /* Make sure the host task fpsimd state is visible to hyp: */
36 ret = kvm_share_hyp(fpsimd, fpsimd + 1);
37 if (ret)
38 return ret;
39
40 return 0;
41 }
42
43 /*
44 * Prepare vcpu for saving the host's FPSIMD state and loading the guest's.
45 * The actual loading is done by the FPSIMD access trap taken to hyp.
46 *
47 * Here, we just set the correct metadata to indicate that the FPSIMD
48 * state in the cpu regs (if any) belongs to current on the host.
49 */
kvm_arch_vcpu_load_fp(struct kvm_vcpu * vcpu)50 void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
51 {
52 BUG_ON(!current->mm);
53
54 if (!system_supports_fpsimd())
55 return;
56
57 /*
58 * Ensure that any host FPSIMD/SVE/SME state is saved and unbound such
59 * that the host kernel is responsible for restoring this state upon
60 * return to userspace, and the hyp code doesn't need to save anything.
61 *
62 * When the host may use SME, fpsimd_save_and_flush_cpu_state() ensures
63 * that PSTATE.{SM,ZA} == {0,0}.
64 */
65 fpsimd_save_and_flush_cpu_state();
66 *host_data_ptr(fp_owner) = FP_STATE_FREE;
67
68 WARN_ON_ONCE(system_supports_sme() && read_sysreg_s(SYS_SVCR));
69 }
70
71 /*
72 * Called just before entering the guest once we are no longer preemptible
73 * and interrupts are disabled. If we have managed to run anything using
74 * FP while we were preemptible (such as off the back of an interrupt),
75 * then neither the host nor the guest own the FP hardware (and it was the
76 * responsibility of the code that used FP to save the existing state).
77 */
kvm_arch_vcpu_ctxflush_fp(struct kvm_vcpu * vcpu)78 void kvm_arch_vcpu_ctxflush_fp(struct kvm_vcpu *vcpu)
79 {
80 if (test_thread_flag(TIF_FOREIGN_FPSTATE))
81 *host_data_ptr(fp_owner) = FP_STATE_FREE;
82 }
83
84 /*
85 * Called just after exiting the guest. If the guest FPSIMD state
86 * was loaded, update the host's context tracking data mark the CPU
87 * FPSIMD regs as dirty and belonging to vcpu so that they will be
88 * written back if the kernel clobbers them due to kernel-mode NEON
89 * before re-entry into the guest.
90 */
kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu * vcpu)91 void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu)
92 {
93 struct cpu_fp_state fp_state;
94
95 WARN_ON_ONCE(!irqs_disabled());
96
97 if (guest_owns_fp_regs()) {
98 /*
99 * Currently we do not support SME guests so SVCR is
100 * always 0 and we just need a variable to point to.
101 */
102 fp_state.st = &vcpu->arch.ctxt.fp_regs;
103 fp_state.sve_state = vcpu->arch.sve_state;
104 fp_state.sve_vl = vcpu->arch.sve_max_vl;
105 fp_state.sme_state = NULL;
106 fp_state.svcr = &__vcpu_sys_reg(vcpu, SVCR);
107 fp_state.fpmr = &__vcpu_sys_reg(vcpu, FPMR);
108 fp_state.fp_type = &vcpu->arch.fp_type;
109
110 if (vcpu_has_sve(vcpu))
111 fp_state.to_save = FP_STATE_SVE;
112 else
113 fp_state.to_save = FP_STATE_FPSIMD;
114
115 fpsimd_bind_state_to_cpu(&fp_state);
116
117 clear_thread_flag(TIF_FOREIGN_FPSTATE);
118 }
119 }
120
121 /*
122 * Write back the vcpu FPSIMD regs if they are dirty, and invalidate the
123 * cpu FPSIMD regs so that they can't be spuriously reused if this vcpu
124 * disappears and another task or vcpu appears that recycles the same
125 * struct fpsimd_state.
126 */
kvm_arch_vcpu_put_fp(struct kvm_vcpu * vcpu)127 void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu)
128 {
129 unsigned long flags;
130
131 local_irq_save(flags);
132
133 if (guest_owns_fp_regs()) {
134 /*
135 * Flush (save and invalidate) the fpsimd/sve state so that if
136 * the host tries to use fpsimd/sve, it's not using stale data
137 * from the guest.
138 *
139 * Flushing the state sets the TIF_FOREIGN_FPSTATE bit for the
140 * context unconditionally, in both nVHE and VHE. This allows
141 * the kernel to restore the fpsimd/sve state, including ZCR_EL1
142 * when needed.
143 */
144 fpsimd_save_and_flush_cpu_state();
145 }
146
147 local_irq_restore(flags);
148 }
149