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/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 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  */
  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  */
  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         vcpu->arch.flags &= ~KVM_ARM64_FP_ENABLED;
  81         vcpu->arch.flags |= KVM_ARM64_FP_HOST;
  82
  83         vcpu->arch.flags &= ~KVM_ARM64_HOST_SVE_ENABLED;
  84         if (read_sysreg(cpacr_el1) & CPACR_EL1_ZEN_EL0EN)
  85                 vcpu->arch.flags |= KVM_ARM64_HOST_SVE_ENABLED;
  86
  87         /*
  88          * We don't currently support SME guests but if we leave
  89          * things in streaming mode then when the guest starts running
  90          * FPSIMD or SVE code it may generate SME traps so as a
  91          * special case if we are in streaming mode we force the host
  92          * state to be saved now and exit streaming mode so that we
  93          * don't have to handle any SME traps for valid guest
  94          * operations. Do this for ZA as well for now for simplicity.
  95          */
  96         if (system_supports_sme()) {
  97                 vcpu->arch.flags &= ~KVM_ARM64_HOST_SME_ENABLED;
  98                 if (read_sysreg(cpacr_el1) & CPACR_EL1_SMEN_EL0EN)
  99                         vcpu->arch.flags |= KVM_ARM64_HOST_SME_ENABLED;
 100
 101                 if (read_sysreg_s(SYS_SVCR) &
 102                     (SVCR_SM_MASK | SVCR_ZA_MASK)) {
 103                         vcpu->arch.flags &= ~KVM_ARM64_FP_HOST;
 104                         fpsimd_save_and_flush_cpu_state();
 105                 }
 106         }
 107 }
 108
 109 /*
 110  * Called just before entering the guest once we are no longer
 111  * preemptable. Syncs the host's TIF_FOREIGN_FPSTATE with the KVM
 112  * mirror of the flag used by the hypervisor.
 113  */
 114 void kvm_arch_vcpu_ctxflush_fp(struct kvm_vcpu *vcpu)
 115 {
 116         if (test_thread_flag(TIF_FOREIGN_FPSTATE))
 117                 vcpu->arch.flags |= KVM_ARM64_FP_FOREIGN_FPSTATE;
 118         else
 119                 vcpu->arch.flags &= ~KVM_ARM64_FP_FOREIGN_FPSTATE;
 120 }
 121
 122 /*
 123  * Called just after exiting the guest. If the guest FPSIMD state
 124  * was loaded, update the host's context tracking data mark the CPU
 125  * FPSIMD regs as dirty and belonging to vcpu so that they will be
 126  * written back if the kernel clobbers them due to kernel-mode NEON
 127  * before re-entry into the guest.
 128  */
 129 void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu)
 130 {
 131         WARN_ON_ONCE(!irqs_disabled());
 132
 133         if (vcpu->arch.flags & KVM_ARM64_FP_ENABLED) {
 134                 /*
 135                  * Currently we do not support SME guests so SVCR is
 136                  * always 0 and we just need a variable to point to.
 137                  */
 138                 fpsimd_bind_state_to_cpu(&vcpu->arch.ctxt.fp_regs,
 139                                          vcpu->arch.sve_state,
 140                                          vcpu->arch.sve_max_vl,
 141                                          NULL, 0, &vcpu->arch.svcr);
 142
 143                 clear_thread_flag(TIF_FOREIGN_FPSTATE);
 144                 update_thread_flag(TIF_SVE, vcpu_has_sve(vcpu));
 145         }
 146 }
 147
 148 /*
 149  * Write back the vcpu FPSIMD regs if they are dirty, and invalidate the
 150  * cpu FPSIMD regs so that they can't be spuriously reused if this vcpu
 151  * disappears and another task or vcpu appears that recycles the same
 152  * struct fpsimd_state.
 153  */
 154 void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu)
 155 {
 156         unsigned long flags;
 157
 158         local_irq_save(flags);
 159
 160         /*
 161          * If we have VHE then the Hyp code will reset CPACR_EL1 to
 162          * CPACR_EL1_DEFAULT and we need to reenable SME.
 163          */
 164         if (has_vhe() && system_supports_sme()) {
 165                 /* Also restore EL0 state seen on entry */
 166                 if (vcpu->arch.flags & KVM_ARM64_HOST_SME_ENABLED)
 167                         sysreg_clear_set(CPACR_EL1, 0,
 168                                          CPACR_EL1_SMEN_EL0EN |
 169                                          CPACR_EL1_SMEN_EL1EN);
 170                 else
 171                         sysreg_clear_set(CPACR_EL1,
 172                                          CPACR_EL1_SMEN_EL0EN,
 173                                          CPACR_EL1_SMEN_EL1EN);
 174         }
 175
 176         if (vcpu->arch.flags & KVM_ARM64_FP_ENABLED) {
 177                 if (vcpu_has_sve(vcpu)) {
 178                         __vcpu_sys_reg(vcpu, ZCR_EL1) = read_sysreg_el1(SYS_ZCR);
 179
 180                         /* Restore the VL that was saved when bound to the CPU */
 181                         if (!has_vhe())
 182                                 sve_cond_update_zcr_vq(vcpu_sve_max_vq(vcpu) - 1,
 183                                                        SYS_ZCR_EL1);
 184                 }
 185
 186                 fpsimd_save_and_flush_cpu_state();
 187         } else if (has_vhe() && system_supports_sve()) {
 188                 /*
 189                  * The FPSIMD/SVE state in the CPU has not been touched, and we
 190                  * have SVE (and VHE): CPACR_EL1 (alias CPTR_EL2) has been
 191                  * reset to CPACR_EL1_DEFAULT by the Hyp code, disabling SVE
 192                  * for EL0.  To avoid spurious traps, restore the trap state
 193                  * seen by kvm_arch_vcpu_load_fp():
 194                  */
 195                 if (vcpu->arch.flags & KVM_ARM64_HOST_SVE_ENABLED)
 196                         sysreg_clear_set(CPACR_EL1, 0, CPACR_EL1_ZEN_EL0EN);
 197                 else
 198                         sysreg_clear_set(CPACR_EL1, CPACR_EL1_ZEN_EL0EN, 0);
 199         }
 200
 201         update_thread_flag(TIF_SVE, 0);
 202
 203         local_irq_restore(flags);
 204 }