fpsimd.c

Go to the documentation of this file.

// SPDX-License-Identifier: GPL-2.0
/*
 * arch/arm64/kvm/fpsimd.c: Guest/host FPSIMD context coordination helpers
 *
 * Copyright 2018 Arm Limited
 * Author: Dave Martin <Dave.Martin@arm.com>
 */
#include <linux/irqflags.h>
#include <linux/sched.h>
#include <linux/kvm_host.h>
#include <asm/fpsimd.h>
#include <asm/kvm_asm.h>
#include <asm/kvm_hyp.h>
#include <asm/kvm_mmu.h>
#include <asm/sysreg.h>
 
void kvm_vcpu_unshare_task_fp(struct kvm_vcpu *vcpu)
{
    struct task_struct *p = vcpu->arch.parent_task;
    struct user_fpsimd_state *fpsimd;
 
    if (!is_protected_kvm_enabled() || !p)
        return;
 
    fpsimd = &p->thread.uw.fpsimd_state;
    kvm_unshare_hyp(fpsimd, fpsimd + 1);
    put_task_struct(p);
}
 
/*
 * Called on entry to KVM_RUN unless this vcpu previously ran at least
 * once and the most recent prior KVM_RUN for this vcpu was called from
 * the same task as current (highly likely).
 *
 * This is guaranteed to execute before kvm_arch_vcpu_load_fp(vcpu),
 * such that on entering hyp the relevant parts of current are already
 * mapped.
 */
int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu)
{
    int ret;
 
    struct user_fpsimd_state *fpsimd = &current->thread.uw.fpsimd_state;
 
    kvm_vcpu_unshare_task_fp(vcpu);
 
    /* Make sure the host task fpsimd state is visible to hyp: */
    ret = kvm_share_hyp(fpsimd, fpsimd + 1);
    if (ret)
        return ret;
 
    vcpu->arch.host_fpsimd_state = kern_hyp_va(fpsimd);
 
    /*
     * We need to keep current's task_struct pinned until its data has been
     * unshared with the hypervisor to make sure it is not re-used by the
     * kernel and donated to someone else while already shared -- see
     * kvm_vcpu_unshare_task_fp() for the matching put_task_struct().
     */
    if (is_protected_kvm_enabled()) {
        get_task_struct(current);
        vcpu->arch.parent_task = current;
    }
 
    return 0;
}
 
/*
 * Prepare vcpu for saving the host's FPSIMD state and loading the guest's.
 * The actual loading is done by the FPSIMD access trap taken to hyp.
 *
 * Here, we just set the correct metadata to indicate that the FPSIMD
 * state in the cpu regs (if any) belongs to current on the host.
 */
void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
{
    BUG_ON(!current->mm);
 
    if (!system_supports_fpsimd())
        return;
 
    fpsimd_kvm_prepare();
 
    /*
     * We will check TIF_FOREIGN_FPSTATE just before entering the
     * guest in kvm_arch_vcpu_ctxflush_fp() and override this to
     * FP_STATE_FREE if the flag set.
     */
    vcpu->arch.fp_state = FP_STATE_HOST_OWNED;
 
    vcpu_clear_flag(vcpu, HOST_SVE_ENABLED);
    if (read_sysreg(cpacr_el1) & CPACR_EL1_ZEN_EL0EN)
        vcpu_set_flag(vcpu, HOST_SVE_ENABLED);
 
    if (system_supports_sme()) {
        vcpu_clear_flag(vcpu, HOST_SME_ENABLED);
        if (read_sysreg(cpacr_el1) & CPACR_EL1_SMEN_EL0EN)
            vcpu_set_flag(vcpu, HOST_SME_ENABLED);
 
        /*
         * If PSTATE.SM is enabled then save any pending FP
         * state and disable PSTATE.SM. If we leave PSTATE.SM
         * enabled and the guest does not enable SME via
         * CPACR_EL1.SMEN then operations that should be valid
         * may generate SME traps from EL1 to EL1 which we
         * can't intercept and which would confuse the guest.
         *
         * Do the same for PSTATE.ZA in the case where there
         * is state in the registers which has not already
         * been saved, this is very unlikely to happen.
         */
        if (read_sysreg_s(SYS_SVCR) & (SVCR_SM_MASK | SVCR_ZA_MASK)) {
            vcpu->arch.fp_state = FP_STATE_FREE;
            fpsimd_save_and_flush_cpu_state();
        }
    }
}
 
/*
 * Called just before entering the guest once we are no longer preemptable
 * and interrupts are disabled. If we have managed to run anything using
 * FP while we were preemptible (such as off the back of an interrupt),
 * then neither the host nor the guest own the FP hardware (and it was the
 * responsibility of the code that used FP to save the existing state).
 */
void kvm_arch_vcpu_ctxflush_fp(struct kvm_vcpu *vcpu)
{
    if (test_thread_flag(TIF_FOREIGN_FPSTATE))
        vcpu->arch.fp_state = FP_STATE_FREE;
}
 
/*
 * Called just after exiting the guest. If the guest FPSIMD state
 * was loaded, update the host's context tracking data mark the CPU
 * FPSIMD regs as dirty and belonging to vcpu so that they will be
 * written back if the kernel clobbers them due to kernel-mode NEON
 * before re-entry into the guest.
 */
void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu)
{
    struct cpu_fp_state fp_state;
 
    WARN_ON_ONCE(!irqs_disabled());
 
    if (vcpu->arch.fp_state == FP_STATE_GUEST_OWNED) {
 
        /*
         * Currently we do not support SME guests so SVCR is
         * always 0 and we just need a variable to point to.
         */
        fp_state.st = &vcpu->arch.ctxt.fp_regs;
        fp_state.sve_state = vcpu->arch.sve_state;
        fp_state.sve_vl = vcpu->arch.sve_max_vl;
        fp_state.sme_state = NULL;
        fp_state.svcr = &vcpu->arch.svcr;
        fp_state.fp_type = &vcpu->arch.fp_type;
 
        if (vcpu_has_sve(vcpu))
            fp_state.to_save = FP_STATE_SVE;
        else
            fp_state.to_save = FP_STATE_FPSIMD;
 
        fpsimd_bind_state_to_cpu(&fp_state);
 
        clear_thread_flag(TIF_FOREIGN_FPSTATE);
    }
}
 
/*
 * Write back the vcpu FPSIMD regs if they are dirty, and invalidate the
 * cpu FPSIMD regs so that they can't be spuriously reused if this vcpu
 * disappears and another task or vcpu appears that recycles the same
 * struct fpsimd_state.
 */
void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu)
{
    unsigned long flags;
 
    local_irq_save(flags);
 
    /*
     * If we have VHE then the Hyp code will reset CPACR_EL1 to
     * the default value and we need to reenable SME.
     */
    if (has_vhe() && system_supports_sme()) {
        /* Also restore EL0 state seen on entry */
        if (vcpu_get_flag(vcpu, HOST_SME_ENABLED))
            sysreg_clear_set(CPACR_EL1, 0,
                     CPACR_EL1_SMEN_EL0EN |
                     CPACR_EL1_SMEN_EL1EN);
        else
            sysreg_clear_set(CPACR_EL1,
                     CPACR_EL1_SMEN_EL0EN,
                     CPACR_EL1_SMEN_EL1EN);
        isb();
    }
 
    if (vcpu->arch.fp_state == FP_STATE_GUEST_OWNED) {
        if (vcpu_has_sve(vcpu)) {
            __vcpu_sys_reg(vcpu, ZCR_EL1) = read_sysreg_el1(SYS_ZCR);
 
            /* Restore the VL that was saved when bound to the CPU */
            if (!has_vhe())
                sve_cond_update_zcr_vq(vcpu_sve_max_vq(vcpu) - 1,
                               SYS_ZCR_EL1);
        }
 
        fpsimd_save_and_flush_cpu_state();
    } else if (has_vhe() && system_supports_sve()) {
        /*
         * The FPSIMD/SVE state in the CPU has not been touched, and we
         * have SVE (and VHE): CPACR_EL1 (alias CPTR_EL2) has been
         * reset by kvm_reset_cptr_el2() in the Hyp code, disabling SVE
         * for EL0.  To avoid spurious traps, restore the trap state
         * seen by kvm_arch_vcpu_load_fp():
         */
        if (vcpu_get_flag(vcpu, HOST_SVE_ENABLED))
            sysreg_clear_set(CPACR_EL1, 0, CPACR_EL1_ZEN_EL0EN);
        else
            sysreg_clear_set(CPACR_EL1, CPACR_EL1_ZEN_EL0EN, 0);
    }
 
    local_irq_restore(flags);
}