arch/arm64/kvm/fpsimd.c

   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/thread_info.h>
  11 #include <linux/kvm_host.h>
  12 #include <asm/fpsimd.h>
  13 #include <asm/kvm_asm.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  */
  26 int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu)
  27 {
  28         int ret;
  29
  30         struct thread_info *ti = &current->thread_info;
  31         struct user_fpsimd_state *fpsimd = &current->thread.uw.fpsimd_state;
  32
  33         /*
  34          * Make sure the host task thread flags and fpsimd state are
  35          * visible to hyp:
  36          */
  37         ret = create_hyp_mappings(ti, ti + 1, PAGE_HYP);
  38         if (ret)
  39                 goto error;
  40
  41         ret = create_hyp_mappings(fpsimd, fpsimd + 1, PAGE_HYP);
  42         if (ret)
  43                 goto error;
  44
  45         vcpu->arch.host_thread_info = kern_hyp_va(ti);
  46         vcpu->arch.host_fpsimd_state = kern_hyp_va(fpsimd);
  47 error:
  48         return ret;
  49 }
  50
  51 /*
  52  * Prepare vcpu for saving the host's FPSIMD state and loading the guest's.
  53  * The actual loading is done by the FPSIMD access trap taken to hyp.
  54  *
  55  * Here, we just set the correct metadata to indicate that the FPSIMD
  56  * state in the cpu regs (if any) belongs to current on the host.
  57  *
  58  * TIF_SVE is backed up here, since it may get clobbered with guest state.
  59  * This flag is restored by kvm_arch_vcpu_put_fp(vcpu).
  60  */
  61 void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
  62 {
  63         BUG_ON(!current->mm);
  64
  65         vcpu->arch.flags &= ~(KVM_ARM64_FP_ENABLED |
  66                               KVM_ARM64_HOST_SVE_IN_USE |
  67                               KVM_ARM64_HOST_SVE_ENABLED);
  68         vcpu->arch.flags |= KVM_ARM64_FP_HOST;
  69
  70         if (test_thread_flag(TIF_SVE))
  71                 vcpu->arch.flags |= KVM_ARM64_HOST_SVE_IN_USE;
  72
  73         if (read_sysreg(cpacr_el1) & CPACR_EL1_ZEN_EL0EN)
  74                 vcpu->arch.flags |= KVM_ARM64_HOST_SVE_ENABLED;
  75 }
  76
  77 /*
  78  * If the guest FPSIMD state was loaded, update the host's context
  79  * tracking data mark the CPU FPSIMD regs as dirty and belonging to vcpu
  80  * so that they will be written back if the kernel clobbers them due to
  81  * kernel-mode NEON before re-entry into the guest.
  82  */
  83 void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu)
  84 {
  85         WARN_ON_ONCE(!irqs_disabled());
  86
  87         if (vcpu->arch.flags & KVM_ARM64_FP_ENABLED) {
  88                 fpsimd_bind_state_to_cpu(&vcpu->arch.ctxt.fp_regs,
  89                                          vcpu->arch.sve_state,
  90                                          vcpu->arch.sve_max_vl);
  91
  92                 clear_thread_flag(TIF_FOREIGN_FPSTATE);
  93                 update_thread_flag(TIF_SVE, vcpu_has_sve(vcpu));
  94         }
  95 }
  96
  97 /*
  98  * Write back the vcpu FPSIMD regs if they are dirty, and invalidate the
  99  * cpu FPSIMD regs so that they can't be spuriously reused if this vcpu
 100  * disappears and another task or vcpu appears that recycles the same
 101  * struct fpsimd_state.
 102  */
 103 void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu)
 104 {
 105         unsigned long flags;
 106         bool host_has_sve = system_supports_sve();
 107         bool guest_has_sve = vcpu_has_sve(vcpu);
 108
 109         local_irq_save(flags);
 110
 111         if (vcpu->arch.flags & KVM_ARM64_FP_ENABLED) {
 112                 fpsimd_save_and_flush_cpu_state();
 113
 114                 if (guest_has_sve)
 115                         __vcpu_sys_reg(vcpu, ZCR_EL1) = read_sysreg_s(SYS_ZCR_EL12);
 116         } else if (host_has_sve) {
 117                 /*
 118                  * The FPSIMD/SVE state in the CPU has not been touched, and we
 119                  * have SVE (and VHE): CPACR_EL1 (alias CPTR_EL2) has been
 120                  * reset to CPACR_EL1_DEFAULT by the Hyp code, disabling SVE
 121                  * for EL0.  To avoid spurious traps, restore the trap state
 122                  * seen by kvm_arch_vcpu_load_fp():
 123                  */
 124                 if (vcpu->arch.flags & KVM_ARM64_HOST_SVE_ENABLED)
 125                         sysreg_clear_set(CPACR_EL1, 0, CPACR_EL1_ZEN_EL0EN);
 126                 else
 127                         sysreg_clear_set(CPACR_EL1, CPACR_EL1_ZEN_EL0EN, 0);
 128         }
 129
 130         update_thread_flag(TIF_SVE,
 131                            vcpu->arch.flags & KVM_ARM64_HOST_SVE_IN_USE);
 132
 133         local_irq_restore(flags);
 134 }