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/*
 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}