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 <Dave.Martin@arm.com>
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 
kvm_vcpu_unshare_task_fp(struct kvm_vcpu * vcpu)17 void kvm_vcpu_unshare_task_fp(struct kvm_vcpu *vcpu)
18 {
19 	struct task_struct *p = vcpu->arch.parent_task;
20 	struct user_fpsimd_state *fpsimd;
21 
22 	if (!is_protected_kvm_enabled() || !p)
23 		return;
24 
25 	fpsimd = &p->thread.uw.fpsimd_state;
26 	kvm_unshare_hyp(fpsimd, fpsimd + 1);
27 	put_task_struct(p);
28 }
29 
30 /*
31  * Called on entry to KVM_RUN unless this vcpu previously ran at least
32  * once and the most recent prior KVM_RUN for this vcpu was called from
33  * the same task as current (highly likely).
34  *
35  * This is guaranteed to execute before kvm_arch_vcpu_load_fp(vcpu),
36  * such that on entering hyp the relevant parts of current are already
37  * mapped.
38  */
kvm_arch_vcpu_run_map_fp(struct kvm_vcpu * vcpu)39 int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu)
40 {
41 	int ret;
42 
43 	struct user_fpsimd_state *fpsimd = &current->thread.uw.fpsimd_state;
44 
45 	kvm_vcpu_unshare_task_fp(vcpu);
46 
47 	/* Make sure the host task fpsimd state is visible to hyp: */
48 	ret = kvm_share_hyp(fpsimd, fpsimd + 1);
49 	if (ret)
50 		return ret;
51 
52 	vcpu->arch.host_fpsimd_state = kern_hyp_va(fpsimd);
53 
54 	/*
55 	 * We need to keep current's task_struct pinned until its data has been
56 	 * unshared with the hypervisor to make sure it is not re-used by the
57 	 * kernel and donated to someone else while already shared -- see
58 	 * kvm_vcpu_unshare_task_fp() for the matching put_task_struct().
59 	 */
60 	if (is_protected_kvm_enabled()) {
61 		get_task_struct(current);
62 		vcpu->arch.parent_task = current;
63 	}
64 
65 	return 0;
66 }
67 
68 /*
69  * Prepare vcpu for saving the host's FPSIMD state and loading the guest's.
70  * The actual loading is done by the FPSIMD access trap taken to hyp.
71  *
72  * Here, we just set the correct metadata to indicate that the FPSIMD
73  * state in the cpu regs (if any) belongs to current on the host.
74  */
kvm_arch_vcpu_load_fp(struct kvm_vcpu * vcpu)75 void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
76 {
77 	BUG_ON(!current->mm);
78 	BUG_ON(test_thread_flag(TIF_SVE));
79 
80 	if (!system_supports_fpsimd())
81 		return;
82 
83 	vcpu->arch.fp_state = FP_STATE_HOST_OWNED;
84 
85 	vcpu_clear_flag(vcpu, HOST_SVE_ENABLED);
86 	if (read_sysreg(cpacr_el1) & CPACR_EL1_ZEN_EL0EN)
87 		vcpu_set_flag(vcpu, HOST_SVE_ENABLED);
88 
89 	/*
90 	 * We don't currently support SME guests but if we leave
91 	 * things in streaming mode then when the guest starts running
92 	 * FPSIMD or SVE code it may generate SME traps so as a
93 	 * special case if we are in streaming mode we force the host
94 	 * state to be saved now and exit streaming mode so that we
95 	 * don't have to handle any SME traps for valid guest
96 	 * operations. Do this for ZA as well for now for simplicity.
97 	 */
98 	if (system_supports_sme()) {
99 		vcpu_clear_flag(vcpu, HOST_SME_ENABLED);
100 		if (read_sysreg(cpacr_el1) & CPACR_EL1_SMEN_EL0EN)
101 			vcpu_set_flag(vcpu, HOST_SME_ENABLED);
102 
103 		if (read_sysreg_s(SYS_SVCR) & (SVCR_SM_MASK | SVCR_ZA_MASK)) {
104 			vcpu->arch.fp_state = FP_STATE_FREE;
105 			fpsimd_save_and_flush_cpu_state();
106 		}
107 	}
108 }
109 
110 /*
111  * Called just before entering the guest once we are no longer preemptable
112  * and interrupts are disabled. If we have managed to run anything using
113  * FP while we were preemptible (such as off the back of an interrupt),
114  * then neither the host nor the guest own the FP hardware (and it was the
115  * responsibility of the code that used FP to save the existing state).
116  */
kvm_arch_vcpu_ctxflush_fp(struct kvm_vcpu * vcpu)117 void kvm_arch_vcpu_ctxflush_fp(struct kvm_vcpu *vcpu)
118 {
119 	if (test_thread_flag(TIF_FOREIGN_FPSTATE))
120 		vcpu->arch.fp_state = FP_STATE_FREE;
121 }
122 
123 /*
124  * Called just after exiting the guest. If the guest FPSIMD state
125  * was loaded, update the host's context tracking data mark the CPU
126  * FPSIMD regs as dirty and belonging to vcpu so that they will be
127  * written back if the kernel clobbers them due to kernel-mode NEON
128  * before re-entry into the guest.
129  */
kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu * vcpu)130 void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu)
131 {
132 	WARN_ON_ONCE(!irqs_disabled());
133 
134 	if (vcpu->arch.fp_state == FP_STATE_GUEST_OWNED) {
135 		/*
136 		 * Currently we do not support SME guests so SVCR is
137 		 * always 0 and we just need a variable to point to.
138 		 */
139 		fpsimd_bind_state_to_cpu(&vcpu->arch.ctxt.fp_regs,
140 					 vcpu->arch.sve_state,
141 					 vcpu->arch.sve_max_vl,
142 					 NULL, 0, &vcpu->arch.svcr);
143 
144 		clear_thread_flag(TIF_FOREIGN_FPSTATE);
145 		update_thread_flag(TIF_SVE, vcpu_has_sve(vcpu));
146 	}
147 }
148 
149 /*
150  * Write back the vcpu FPSIMD regs if they are dirty, and invalidate the
151  * cpu FPSIMD regs so that they can't be spuriously reused if this vcpu
152  * disappears and another task or vcpu appears that recycles the same
153  * struct fpsimd_state.
154  */
kvm_arch_vcpu_put_fp(struct kvm_vcpu * vcpu)155 void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu)
156 {
157 	unsigned long flags;
158 
159 	local_irq_save(flags);
160 
161 	/*
162 	 * If we have VHE then the Hyp code will reset CPACR_EL1 to
163 	 * CPACR_EL1_DEFAULT and we need to reenable SME.
164 	 */
165 	if (has_vhe() && system_supports_sme()) {
166 		/* Also restore EL0 state seen on entry */
167 		if (vcpu_get_flag(vcpu, HOST_SME_ENABLED))
168 			sysreg_clear_set(CPACR_EL1, 0,
169 					 CPACR_EL1_SMEN_EL0EN |
170 					 CPACR_EL1_SMEN_EL1EN);
171 		else
172 			sysreg_clear_set(CPACR_EL1,
173 					 CPACR_EL1_SMEN_EL0EN,
174 					 CPACR_EL1_SMEN_EL1EN);
175 	}
176 
177 	if (vcpu->arch.fp_state == FP_STATE_GUEST_OWNED) {
178 		if (vcpu_has_sve(vcpu)) {
179 			__vcpu_sys_reg(vcpu, ZCR_EL1) = read_sysreg_el1(SYS_ZCR);
180 
181 			/* Restore the VL that was saved when bound to the CPU */
182 			if (!has_vhe())
183 				sve_cond_update_zcr_vq(vcpu_sve_max_vq(vcpu) - 1,
184 						       SYS_ZCR_EL1);
185 		}
186 
187 		fpsimd_save_and_flush_cpu_state();
188 	} else if (has_vhe() && system_supports_sve()) {
189 		/*
190 		 * The FPSIMD/SVE state in the CPU has not been touched, and we
191 		 * have SVE (and VHE): CPACR_EL1 (alias CPTR_EL2) has been
192 		 * reset to CPACR_EL1_DEFAULT by the Hyp code, disabling SVE
193 		 * for EL0.  To avoid spurious traps, restore the trap state
194 		 * seen by kvm_arch_vcpu_load_fp():
195 		 */
196 		if (vcpu_get_flag(vcpu, HOST_SVE_ENABLED))
197 			sysreg_clear_set(CPACR_EL1, 0, CPACR_EL1_ZEN_EL0EN);
198 		else
199 			sysreg_clear_set(CPACR_EL1, CPACR_EL1_ZEN_EL0EN, 0);
200 	}
201 
202 	update_thread_flag(TIF_SVE, 0);
203 
204 	local_irq_restore(flags);
205 }
206