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2955bcc8c3
Commite6b673b("KVM: arm64: Optimise FPSIMD handling to reduce guest/host thrashing") uses fpsimd_save() to save the FPSIMD state for a vcpu when scheduling the vcpu out. However, currently current's value of TIF_SVE is restored before calling fpsimd_save() which means that fpsimd_save() may erroneously attempt to save SVE state from the vcpu. This enables current's vector state to be polluted with guest data. current->thread.sve_state may be unallocated or not large enough, so this can also trigger a NULL dereference or buffer overrun. Instead of this, TIF_SVE should be configured properly for the guest when calling fpsimd_save() with the vcpu context loaded. This patch ensures this by delaying restoration of current's TIF_SVE until after the call to fpsimd_save(). Fixes:e6b673b741("KVM: arm64: Optimise FPSIMD handling to reduce guest/host thrashing") Signed-off-by: Dave Martin <Dave.Martin@arm.com> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
129 lines
3.8 KiB
C
129 lines
3.8 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/kvm_asm.h>
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#include <asm/kvm_host.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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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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* TIF_SVE is backed up here, since it may get clobbered with guest state.
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* This flag is restored by kvm_arch_vcpu_put_fp(vcpu).
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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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vcpu->arch.flags &= ~(KVM_ARM64_FP_ENABLED |
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KVM_ARM64_HOST_SVE_IN_USE |
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KVM_ARM64_HOST_SVE_ENABLED);
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vcpu->arch.flags |= KVM_ARM64_FP_HOST;
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if (test_thread_flag(TIF_SVE))
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vcpu->arch.flags |= KVM_ARM64_HOST_SVE_IN_USE;
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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.gp_regs.fp_regs);
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clear_thread_flag(TIF_FOREIGN_FPSTATE);
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clear_thread_flag(TIF_SVE);
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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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/* Clean guest FP state to memory and invalidate cpu view */
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fpsimd_save();
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fpsimd_flush_cpu_state();
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} else if (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,
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vcpu->arch.flags & KVM_ARM64_HOST_SVE_IN_USE);
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local_irq_restore(flags);
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}
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