8383741ab2
The SVE host tracking in KVM is pretty involved. It relies on a set of flags tracking the ownership of the SVE register, as well as that of the EL0 access. It is also pretty scary: __hyp_sve_save_host() computes a thread_struct pointer and obtains a sve_state which gets directly accessed without further ado, even on nVHE. How can this even work? The answer to that is that it doesn't, and that this is mostly dead code. Closer examination shows that on executing a syscall, userspace loses its SVE state entirely. This is part of the ABI. Another thing to notice is that although the kernel provides helpers such as kernel_neon_begin()/end(), they only deal with the FP/NEON state, and not SVE. Given that you can only execute a guest as the result of a syscall, and that the kernel cannot use SVE by itself, it becomes pretty obvious that there is never any host SVE state to save, and that this code is only there to increase confusion. Get rid of the TIF_SVE tracking and host save infrastructure altogether. Reviewed-by: Mark Brown <broonie@kernel.org> Signed-off-by: Marc Zyngier <maz@kernel.org>
143 lines
4.0 KiB
C
143 lines
4.0 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* arch/arm64/kvm/fpsimd.c: Guest/host FPSIMD context coordination helpers
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*
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* Copyright 2018 Arm Limited
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* Author: Dave Martin <Dave.Martin@arm.com>
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*/
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#include <linux/irqflags.h>
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#include <linux/sched.h>
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#include <linux/thread_info.h>
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#include <linux/kvm_host.h>
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#include <asm/fpsimd.h>
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#include <asm/kvm_asm.h>
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#include <asm/kvm_hyp.h>
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#include <asm/kvm_mmu.h>
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#include <asm/sysreg.h>
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/*
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* Called on entry to KVM_RUN unless this vcpu previously ran at least
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* once and the most recent prior KVM_RUN for this vcpu was called from
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* the same task as current (highly likely).
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*
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* This is guaranteed to execute before kvm_arch_vcpu_load_fp(vcpu),
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* such that on entering hyp the relevant parts of current are already
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* mapped.
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*/
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int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu)
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{
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int ret;
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struct thread_info *ti = ¤t->thread_info;
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struct user_fpsimd_state *fpsimd = ¤t->thread.uw.fpsimd_state;
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/*
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* Make sure the host task thread flags and fpsimd state are
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* visible to hyp:
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*/
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ret = create_hyp_mappings(ti, ti + 1, PAGE_HYP);
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if (ret)
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goto error;
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ret = create_hyp_mappings(fpsimd, fpsimd + 1, PAGE_HYP);
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if (ret)
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goto error;
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if (vcpu->arch.sve_state) {
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void *sve_end;
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sve_end = vcpu->arch.sve_state + vcpu_sve_state_size(vcpu);
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ret = create_hyp_mappings(vcpu->arch.sve_state, sve_end,
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PAGE_HYP);
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if (ret)
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goto error;
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}
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vcpu->arch.host_thread_info = kern_hyp_va(ti);
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vcpu->arch.host_fpsimd_state = kern_hyp_va(fpsimd);
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error:
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return ret;
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}
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/*
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* Prepare vcpu for saving the host's FPSIMD state and loading the guest's.
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* The actual loading is done by the FPSIMD access trap taken to hyp.
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*
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* Here, we just set the correct metadata to indicate that the FPSIMD
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* state in the cpu regs (if any) belongs to current on the host.
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*/
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void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
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{
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BUG_ON(!current->mm);
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BUG_ON(test_thread_flag(TIF_SVE));
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vcpu->arch.flags &= ~KVM_ARM64_FP_ENABLED;
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vcpu->arch.flags |= KVM_ARM64_FP_HOST;
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if (read_sysreg(cpacr_el1) & CPACR_EL1_ZEN_EL0EN)
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vcpu->arch.flags |= KVM_ARM64_HOST_SVE_ENABLED;
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}
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/*
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* If the guest FPSIMD state was loaded, update the host's context
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* tracking data mark the CPU FPSIMD regs as dirty and belonging to vcpu
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* so that they will be written back if the kernel clobbers them due to
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* kernel-mode NEON before re-entry into the guest.
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*/
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void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu)
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{
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WARN_ON_ONCE(!irqs_disabled());
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if (vcpu->arch.flags & KVM_ARM64_FP_ENABLED) {
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fpsimd_bind_state_to_cpu(&vcpu->arch.ctxt.fp_regs,
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vcpu->arch.sve_state,
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vcpu->arch.sve_max_vl);
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clear_thread_flag(TIF_FOREIGN_FPSTATE);
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update_thread_flag(TIF_SVE, vcpu_has_sve(vcpu));
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}
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}
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/*
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* Write back the vcpu FPSIMD regs if they are dirty, and invalidate the
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* cpu FPSIMD regs so that they can't be spuriously reused if this vcpu
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* disappears and another task or vcpu appears that recycles the same
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* struct fpsimd_state.
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*/
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void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu)
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{
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unsigned long flags;
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local_irq_save(flags);
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if (vcpu->arch.flags & KVM_ARM64_FP_ENABLED) {
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if (vcpu_has_sve(vcpu)) {
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__vcpu_sys_reg(vcpu, ZCR_EL1) = read_sysreg_el1(SYS_ZCR);
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/* Restore the VL that was saved when bound to the CPU */
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if (!has_vhe())
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sve_cond_update_zcr_vq(vcpu_sve_max_vq(vcpu) - 1,
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SYS_ZCR_EL1);
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}
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fpsimd_save_and_flush_cpu_state();
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} else if (has_vhe() && system_supports_sve()) {
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/*
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* The FPSIMD/SVE state in the CPU has not been touched, and we
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* have SVE (and VHE): CPACR_EL1 (alias CPTR_EL2) has been
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* reset to CPACR_EL1_DEFAULT by the Hyp code, disabling SVE
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* for EL0. To avoid spurious traps, restore the trap state
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* seen by kvm_arch_vcpu_load_fp():
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*/
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if (vcpu->arch.flags & KVM_ARM64_HOST_SVE_ENABLED)
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sysreg_clear_set(CPACR_EL1, 0, CPACR_EL1_ZEN_EL0EN);
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else
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sysreg_clear_set(CPACR_EL1, CPACR_EL1_ZEN_EL0EN, 0);
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}
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update_thread_flag(TIF_SVE, 0);
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local_irq_restore(flags);
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}
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