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
17/*
18 * Prepare vcpu for saving the host's FPSIMD state and loading the guest's.
19 * The actual loading is done by the FPSIMD access trap taken to hyp.
20 *
21 * Here, we just set the correct metadata to indicate that the FPSIMD
22 * state in the cpu regs (if any) belongs to current on the host.
23 */
24void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
25{
26 BUG_ON(!current->mm);
27
28 if (!system_supports_fpsimd())
29 return;
30
31 /*
32 * Ensure that any host FPSIMD/SVE/SME state is saved and unbound such
33 * that the host kernel is responsible for restoring this state upon
34 * return to userspace, and the hyp code doesn't need to save anything.
35 *
36 * When the host may use SME, fpsimd_save_and_flush_cpu_state() ensures
37 * that PSTATE.{SM,ZA} == {0,0}.
38 */
39 fpsimd_save_and_flush_cpu_state();
40 *host_data_ptr(fp_owner) = FP_STATE_FREE;
41
42 WARN_ON_ONCE(system_supports_sme() && read_sysreg_s(SYS_SVCR));
43}
44
45/*
46 * Called just before entering the guest once we are no longer preemptible
47 * and interrupts are disabled. If we have managed to run anything using
48 * FP while we were preemptible (such as off the back of an interrupt),
49 * then neither the host nor the guest own the FP hardware (and it was the
50 * responsibility of the code that used FP to save the existing state).
51 */
52void kvm_arch_vcpu_ctxflush_fp(struct kvm_vcpu *vcpu)
53{
54 if (test_thread_flag(TIF_FOREIGN_FPSTATE))
55 *host_data_ptr(fp_owner) = FP_STATE_FREE;
56}
57
58/*
59 * Called just after exiting the guest. If the guest FPSIMD state
60 * was loaded, update the host's context tracking data mark the CPU
61 * FPSIMD regs as dirty and belonging to vcpu so that they will be
62 * written back if the kernel clobbers them due to kernel-mode NEON
63 * before re-entry into the guest.
64 */
65void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu)
66{
67 struct cpu_fp_state fp_state;
68
69 WARN_ON_ONCE(!irqs_disabled());
70
71 if (guest_owns_fp_regs()) {
72 /*
73 * Currently we do not support SME guests so SVCR is
74 * always 0 and we just need a variable to point to.
75 */
76 fp_state.st = &vcpu->arch.ctxt.fp_regs;
77 fp_state.sve_state = vcpu->arch.sve_state;
78 fp_state.sve_vl = vcpu->arch.sve_max_vl;
79 fp_state.sme_state = NULL;
80 fp_state.svcr = __ctxt_sys_reg(&vcpu->arch.ctxt, SVCR);
81 fp_state.fpmr = __ctxt_sys_reg(&vcpu->arch.ctxt, FPMR);
82 fp_state.fp_type = &vcpu->arch.fp_type;
83
84 if (vcpu_has_sve(vcpu))
85 fp_state.to_save = FP_STATE_SVE;
86 else
87 fp_state.to_save = FP_STATE_FPSIMD;
88
89 fpsimd_bind_state_to_cpu(&fp_state);
90
91 clear_thread_flag(TIF_FOREIGN_FPSTATE);
92 }
93}
94
95/*
96 * Write back the vcpu FPSIMD regs if they are dirty, and invalidate the
97 * cpu FPSIMD regs so that they can't be spuriously reused if this vcpu
98 * disappears and another task or vcpu appears that recycles the same
99 * struct fpsimd_state.
100 */
101void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu)
102{
103 unsigned long flags;
104
105 local_irq_save(flags);
106
107 if (guest_owns_fp_regs()) {
108 /*
109 * Flush (save and invalidate) the fpsimd/sve state so that if
110 * the host tries to use fpsimd/sve, it's not using stale data
111 * from the guest.
112 *
113 * Flushing the state sets the TIF_FOREIGN_FPSTATE bit for the
114 * context unconditionally, in both nVHE and VHE. This allows
115 * the kernel to restore the fpsimd/sve state, including ZCR_EL1
116 * when needed.
117 */
118 fpsimd_save_and_flush_cpu_state();
119 }
120
121 local_irq_restore(flags);
122}
123

source code of linux/arch/arm64/kvm/fpsimd.c