xref: /openbmc/linux/arch/arm64/kvm/fpsimd.c (revision 75c76ab5)
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 
79 	if (!system_supports_fpsimd())
80 		return;
81 
82 	fpsimd_kvm_prepare();
83 
84 	/*
85 	 * We will check TIF_FOREIGN_FPSTATE just before entering the
86 	 * guest in kvm_arch_vcpu_ctxflush_fp() and override this to
87 	 * FP_STATE_FREE if the flag set.
88 	 */
89 	vcpu->arch.fp_state = FP_STATE_HOST_OWNED;
90 
91 	vcpu_clear_flag(vcpu, HOST_SVE_ENABLED);
92 	if (read_sysreg(cpacr_el1) & CPACR_EL1_ZEN_EL0EN)
93 		vcpu_set_flag(vcpu, HOST_SVE_ENABLED);
94 
95 	if (system_supports_sme()) {
96 		vcpu_clear_flag(vcpu, HOST_SME_ENABLED);
97 		if (read_sysreg(cpacr_el1) & CPACR_EL1_SMEN_EL0EN)
98 			vcpu_set_flag(vcpu, HOST_SME_ENABLED);
99 
100 		/*
101 		 * If PSTATE.SM is enabled then save any pending FP
102 		 * state and disable PSTATE.SM. If we leave PSTATE.SM
103 		 * enabled and the guest does not enable SME via
104 		 * CPACR_EL1.SMEN then operations that should be valid
105 		 * may generate SME traps from EL1 to EL1 which we
106 		 * can't intercept and which would confuse the guest.
107 		 *
108 		 * Do the same for PSTATE.ZA in the case where there
109 		 * is state in the registers which has not already
110 		 * been saved, this is very unlikely to happen.
111 		 */
112 		if (read_sysreg_s(SYS_SVCR) & (SVCR_SM_MASK | SVCR_ZA_MASK)) {
113 			vcpu->arch.fp_state = FP_STATE_FREE;
114 			fpsimd_save_and_flush_cpu_state();
115 		}
116 	}
117 }
118 
119 /*
120  * Called just before entering the guest once we are no longer preemptable
121  * and interrupts are disabled. If we have managed to run anything using
122  * FP while we were preemptible (such as off the back of an interrupt),
123  * then neither the host nor the guest own the FP hardware (and it was the
124  * responsibility of the code that used FP to save the existing state).
125  */
kvm_arch_vcpu_ctxflush_fp(struct kvm_vcpu * vcpu)126 void kvm_arch_vcpu_ctxflush_fp(struct kvm_vcpu *vcpu)
127 {
128 	if (test_thread_flag(TIF_FOREIGN_FPSTATE))
129 		vcpu->arch.fp_state = FP_STATE_FREE;
130 }
131 
132 /*
133  * Called just after exiting the guest. If the guest FPSIMD state
134  * was loaded, update the host's context tracking data mark the CPU
135  * FPSIMD regs as dirty and belonging to vcpu so that they will be
136  * written back if the kernel clobbers them due to kernel-mode NEON
137  * before re-entry into the guest.
138  */
kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu * vcpu)139 void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu)
140 {
141 	struct cpu_fp_state fp_state;
142 
143 	WARN_ON_ONCE(!irqs_disabled());
144 
145 	if (vcpu->arch.fp_state == FP_STATE_GUEST_OWNED) {
146 
147 		/*
148 		 * Currently we do not support SME guests so SVCR is
149 		 * always 0 and we just need a variable to point to.
150 		 */
151 		fp_state.st = &vcpu->arch.ctxt.fp_regs;
152 		fp_state.sve_state = vcpu->arch.sve_state;
153 		fp_state.sve_vl = vcpu->arch.sve_max_vl;
154 		fp_state.sme_state = NULL;
155 		fp_state.svcr = &vcpu->arch.svcr;
156 		fp_state.fp_type = &vcpu->arch.fp_type;
157 
158 		if (vcpu_has_sve(vcpu))
159 			fp_state.to_save = FP_STATE_SVE;
160 		else
161 			fp_state.to_save = FP_STATE_FPSIMD;
162 
163 		fpsimd_bind_state_to_cpu(&fp_state);
164 
165 		clear_thread_flag(TIF_FOREIGN_FPSTATE);
166 	}
167 }
168 
169 /*
170  * Write back the vcpu FPSIMD regs if they are dirty, and invalidate the
171  * cpu FPSIMD regs so that they can't be spuriously reused if this vcpu
172  * disappears and another task or vcpu appears that recycles the same
173  * struct fpsimd_state.
174  */
kvm_arch_vcpu_put_fp(struct kvm_vcpu * vcpu)175 void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu)
176 {
177 	unsigned long flags;
178 
179 	local_irq_save(flags);
180 
181 	/*
182 	 * If we have VHE then the Hyp code will reset CPACR_EL1 to
183 	 * the default value and we need to reenable SME.
184 	 */
185 	if (has_vhe() && system_supports_sme()) {
186 		/* Also restore EL0 state seen on entry */
187 		if (vcpu_get_flag(vcpu, HOST_SME_ENABLED))
188 			sysreg_clear_set(CPACR_EL1, 0,
189 					 CPACR_EL1_SMEN_EL0EN |
190 					 CPACR_EL1_SMEN_EL1EN);
191 		else
192 			sysreg_clear_set(CPACR_EL1,
193 					 CPACR_EL1_SMEN_EL0EN,
194 					 CPACR_EL1_SMEN_EL1EN);
195 		isb();
196 	}
197 
198 	if (vcpu->arch.fp_state == FP_STATE_GUEST_OWNED) {
199 		if (vcpu_has_sve(vcpu)) {
200 			__vcpu_sys_reg(vcpu, ZCR_EL1) = read_sysreg_el1(SYS_ZCR);
201 
202 			/* Restore the VL that was saved when bound to the CPU */
203 			if (!has_vhe())
204 				sve_cond_update_zcr_vq(vcpu_sve_max_vq(vcpu) - 1,
205 						       SYS_ZCR_EL1);
206 		}
207 
208 		fpsimd_save_and_flush_cpu_state();
209 	} else if (has_vhe() && system_supports_sve()) {
210 		/*
211 		 * The FPSIMD/SVE state in the CPU has not been touched, and we
212 		 * have SVE (and VHE): CPACR_EL1 (alias CPTR_EL2) has been
213 		 * reset by kvm_reset_cptr_el2() in the Hyp code, disabling SVE
214 		 * for EL0.  To avoid spurious traps, restore the trap state
215 		 * seen by kvm_arch_vcpu_load_fp():
216 		 */
217 		if (vcpu_get_flag(vcpu, HOST_SVE_ENABLED))
218 			sysreg_clear_set(CPACR_EL1, 0, CPACR_EL1_ZEN_EL0EN);
219 		else
220 			sysreg_clear_set(CPACR_EL1, CPACR_EL1_ZEN_EL0EN, 0);
221 	}
222 
223 	local_irq_restore(flags);
224 }
225