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_host.h>
  15 #include <asm/kvm_mmu.h>
  16 #include <asm/sysreg.h>
  17
  18 /*
  19  * Called on entry to KVM_RUN unless this vcpu previously ran at least
  20  * once and the most recent prior KVM_RUN for this vcpu was called from
  21  * the same task as current (highly likely).
  22  *
  23  * This is guaranteed to execute before kvm_arch_vcpu_load_fp(vcpu),
  24  * such that on entering hyp the relevant parts of current are already
  25  * mapped.
  26  */
  27 int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu)
  28 {
  29         int ret;
  30
  31         struct thread_info *ti = &current->thread_info;
  32         struct user_fpsimd_state *fpsimd = &current->thread.uw.fpsimd_state;
  33
  34         /*
  35          * Make sure the host task thread flags and fpsimd state are
  36          * visible to hyp:
  37          */
  38         ret = create_hyp_mappings(ti, ti + 1, PAGE_HYP);
  39         if (ret)
  40                 goto error;
  41
  42         ret = create_hyp_mappings(fpsimd, fpsimd + 1, PAGE_HYP);
  43         if (ret)
  44                 goto error;
  45
  46         vcpu->arch.host_thread_info = kern_hyp_va(ti);
  47         vcpu->arch.host_fpsimd_state = kern_hyp_va(fpsimd);
  48 error:
  49         return ret;
  50 }
  51
  52 /*
  53  * Prepare vcpu for saving the host's FPSIMD state and loading the guest's.
  54  * The actual loading is done by the FPSIMD access trap taken to hyp.
  55  *
  56  * Here, we just set the correct metadata to indicate that the FPSIMD
  57  * state in the cpu regs (if any) belongs to current on the host.
  58  *
  59  * TIF_SVE is backed up here, since it may get clobbered with guest state.
  60  * This flag is restored by kvm_arch_vcpu_put_fp(vcpu).
  61  */
  62 void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
  63 {
  64         BUG_ON(!current->mm);
  65
  66         vcpu->arch.flags &= ~(KVM_ARM64_FP_ENABLED |
  67                               KVM_ARM64_HOST_SVE_IN_USE |
  68                               KVM_ARM64_HOST_SVE_ENABLED);
  69         vcpu->arch.flags |= KVM_ARM64_FP_HOST;
  70
  71         if (test_thread_flag(TIF_SVE))
  72                 vcpu->arch.flags |= KVM_ARM64_HOST_SVE_IN_USE;
  73
  74         if (read_sysreg(cpacr_el1) & CPACR_EL1_ZEN_EL0EN)
  75                 vcpu->arch.flags |= KVM_ARM64_HOST_SVE_ENABLED;
  76 }
  77
  78 /*
  79  * If the guest FPSIMD state was loaded, update the host's context
  80  * tracking data mark the CPU FPSIMD regs as dirty and belonging to vcpu
  81  * so that they will be written back if the kernel clobbers them due to
  82  * kernel-mode NEON before re-entry into the guest.
  83  */
  84 void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu)
  85 {
  86         WARN_ON_ONCE(!irqs_disabled());
  87
  88         if (vcpu->arch.flags & KVM_ARM64_FP_ENABLED) {
  89                 fpsimd_bind_state_to_cpu(&vcpu->arch.ctxt.gp_regs.fp_regs,
  90                                          vcpu->arch.sve_state,
  91                                          vcpu->arch.sve_max_vl);
  92
  93                 clear_thread_flag(TIF_FOREIGN_FPSTATE);
  94                 update_thread_flag(TIF_SVE, vcpu_has_sve(vcpu));
  95         }
  96 }
  97
  98 /*
  99  * Write back the vcpu FPSIMD regs if they are dirty, and invalidate the
 100  * cpu FPSIMD regs so that they can't be spuriously reused if this vcpu
 101  * disappears and another task or vcpu appears that recycles the same
 102  * struct fpsimd_state.
 103  */
 104 void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu)
 105 {
 106         unsigned long flags;
 107         bool host_has_sve = system_supports_sve();
 108         bool guest_has_sve = vcpu_has_sve(vcpu);
 109
 110         local_irq_save(flags);
 111
 112         if (vcpu->arch.flags & KVM_ARM64_FP_ENABLED) {
 113                 u64 *guest_zcr = &vcpu->arch.ctxt.sys_regs[ZCR_EL1];
 114
 115                 fpsimd_save_and_flush_cpu_state();
 116
 117                 if (guest_has_sve)
 118                         *guest_zcr = read_sysreg_s(SYS_ZCR_EL12);
 119         } else if (host_has_sve) {
 120                 /*
 121                  * The FPSIMD/SVE state in the CPU has not been touched, and we
 122                  * have SVE (and VHE): CPACR_EL1 (alias CPTR_EL2) has been
 123                  * reset to CPACR_EL1_DEFAULT by the Hyp code, disabling SVE
 124                  * for EL0.  To avoid spurious traps, restore the trap state
 125                  * seen by kvm_arch_vcpu_load_fp():
 126                  */
 127                 if (vcpu->arch.flags & KVM_ARM64_HOST_SVE_ENABLED)
 128                         sysreg_clear_set(CPACR_EL1, 0, CPACR_EL1_ZEN_EL0EN);
 129                 else
 130                         sysreg_clear_set(CPACR_EL1, CPACR_EL1_ZEN_EL0EN, 0);
 131         }
 132
 133         update_thread_flag(TIF_SVE,
 134                            vcpu->arch.flags & KVM_ARM64_HOST_SVE_IN_USE);
 135
 136         local_irq_restore(flags);
 137 }