KVM: x86: KVM_CAP_SYNC_REGS
This commit implements an enhanced x86 version of S390 KVM_CAP_SYNC_REGS functionality. KVM_CAP_SYNC_REGS "allow[s] userspace to access certain guest registers without having to call SET/GET_*REGS”. This reduces ioctl overhead which is particularly important when userspace is making synchronous guest state modifications (e.g. when emulating and/or intercepting instructions). Originally implemented upstream for the S390, the x86 differences follow: - userspace can select the register sets to be synchronized with kvm_run using bit-flags in the kvm_valid_registers and kvm_dirty_registers fields. - vcpu_events is available in addition to the regs and sregs register sets. Signed-off-by: Ken Hofsass <hofsass@google.com> Reviewed-by: David Hildenbrand <david@redhat.com> [Removed wrapper around check for reserved kvm_valid_regs. - Radim] Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
This commit is contained in:
Ken Hofsass
Radim Krčmář
parent
7b7e39522a
commit
01643c51bf
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@ -4110,6 +4110,46 @@ Once this is done the KVM_REG_MIPS_VEC_* and KVM_REG_MIPS_MSA_* registers can be
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accessed, and the Config5.MSAEn bit is accessible via the KVM API and also from
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the guest.
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6.74 KVM_CAP_SYNC_REGS
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Architectures: s390, x86
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Target: s390: always enabled, x86: vcpu
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Parameters: none
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Returns: x86: KVM_CHECK_EXTENSION returns a bit-array indicating which register
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sets are supported (bitfields defined in arch/x86/include/uapi/asm/kvm.h).
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As described above in the kvm_sync_regs struct info in section 5 (kvm_run):
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KVM_CAP_SYNC_REGS "allow[s] userspace to access certain guest registers
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without having to call SET/GET_*REGS". This reduces overhead by eliminating
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repeated ioctl calls for setting and/or getting register values. This is
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particularly important when userspace is making synchronous guest state
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modifications, e.g. when emulating and/or intercepting instructions in
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userspace.
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For s390 specifics, please refer to the source code.
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For x86:
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- the register sets to be copied out to kvm_run are selectable
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by userspace (rather that all sets being copied out for every exit).
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- vcpu_events are available in addition to regs and sregs.
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For x86, the 'kvm_valid_regs' field of struct kvm_run is overloaded to
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function as an input bit-array field set by userspace to indicate the
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specific register sets to be copied out on the next exit.
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To indicate when userspace has modified values that should be copied into
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the vCPU, the all architecture bitarray field, 'kvm_dirty_regs' must be set.
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This is done using the same bitflags as for the 'kvm_valid_regs' field.
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If the dirty bit is not set, then the register set values will not be copied
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into the vCPU even if they've been modified.
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Unused bitfields in the bitarrays must be set to zero.
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struct kvm_sync_regs {
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struct kvm_regs regs;
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struct kvm_sregs sregs;
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struct kvm_vcpu_events events;
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};
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7. Capabilities that can be enabled on VMs
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------------------------------------------
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@ -354,8 +354,25 @@ struct kvm_xcrs {
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__u64 padding[16];
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};
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/* definition of registers in kvm_run */
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#define KVM_SYNC_X86_REGS (1UL << 0)
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#define KVM_SYNC_X86_SREGS (1UL << 1)
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#define KVM_SYNC_X86_EVENTS (1UL << 2)
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#define KVM_SYNC_X86_VALID_FIELDS \
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(KVM_SYNC_X86_REGS| \
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KVM_SYNC_X86_SREGS| \
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KVM_SYNC_X86_EVENTS)
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/* kvm_sync_regs struct included by kvm_run struct */
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struct kvm_sync_regs {
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/* Members of this structure are potentially malicious.
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* Care must be taken by code reading, esp. interpreting,
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* data fields from them inside KVM to prevent TOCTOU and
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* double-fetch types of vulnerabilities.
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*/
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struct kvm_regs regs;
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struct kvm_sregs sregs;
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struct kvm_vcpu_events events;
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};
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#define KVM_X86_QUIRK_LINT0_REENABLED (1 << 0)
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@ -102,6 +102,8 @@ static void update_cr8_intercept(struct kvm_vcpu *vcpu);
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static void process_nmi(struct kvm_vcpu *vcpu);
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static void enter_smm(struct kvm_vcpu *vcpu);
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static void __kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags);
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static void store_regs(struct kvm_vcpu *vcpu);
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static int sync_regs(struct kvm_vcpu *vcpu);
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struct kvm_x86_ops *kvm_x86_ops __read_mostly;
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EXPORT_SYMBOL_GPL(kvm_x86_ops);
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@ -2829,6 +2831,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
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case KVM_CAP_GET_MSR_FEATURES:
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r = 1;
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break;
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case KVM_CAP_SYNC_REGS:
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r = KVM_SYNC_X86_VALID_FIELDS;
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break;
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case KVM_CAP_ADJUST_CLOCK:
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r = KVM_CLOCK_TSC_STABLE;
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break;
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@ -7510,7 +7515,6 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
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return 0;
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}
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int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
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{
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int r;
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@ -7536,6 +7540,17 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
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goto out;
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}
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if (vcpu->run->kvm_valid_regs & ~KVM_SYNC_X86_VALID_FIELDS) {
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r = -EINVAL;
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goto out;
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}
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if (vcpu->run->kvm_dirty_regs) {
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r = sync_regs(vcpu);
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if (r != 0)
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goto out;
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}
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/* re-sync apic's tpr */
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if (!lapic_in_kernel(vcpu)) {
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if (kvm_set_cr8(vcpu, kvm_run->cr8) != 0) {
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@ -7560,6 +7575,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
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out:
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kvm_put_guest_fpu(vcpu);
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if (vcpu->run->kvm_valid_regs)
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store_regs(vcpu);
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post_kvm_run_save(vcpu);
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kvm_sigset_deactivate(vcpu);
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@ -7567,10 +7584,8 @@ out:
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return r;
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}
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int kvm_arch_vcpu_ioctl_get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
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static void __get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
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{
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vcpu_load(vcpu);
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if (vcpu->arch.emulate_regs_need_sync_to_vcpu) {
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/*
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* We are here if userspace calls get_regs() in the middle of
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@ -7603,15 +7618,18 @@ int kvm_arch_vcpu_ioctl_get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
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regs->rip = kvm_rip_read(vcpu);
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regs->rflags = kvm_get_rflags(vcpu);
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}
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int kvm_arch_vcpu_ioctl_get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
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{
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vcpu_load(vcpu);
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__get_regs(vcpu, regs);
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vcpu_put(vcpu);
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return 0;
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}
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int kvm_arch_vcpu_ioctl_set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
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static void __set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
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{
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vcpu_load(vcpu);
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vcpu->arch.emulate_regs_need_sync_from_vcpu = true;
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vcpu->arch.emulate_regs_need_sync_to_vcpu = false;
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@ -7640,7 +7658,12 @@ int kvm_arch_vcpu_ioctl_set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
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vcpu->arch.exception.pending = false;
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kvm_make_request(KVM_REQ_EVENT, vcpu);
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}
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int kvm_arch_vcpu_ioctl_set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
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{
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vcpu_load(vcpu);
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__set_regs(vcpu, regs);
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vcpu_put(vcpu);
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return 0;
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}
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@ -7655,13 +7678,10 @@ void kvm_get_cs_db_l_bits(struct kvm_vcpu *vcpu, int *db, int *l)
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}
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EXPORT_SYMBOL_GPL(kvm_get_cs_db_l_bits);
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int kvm_arch_vcpu_ioctl_get_sregs(struct kvm_vcpu *vcpu,
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struct kvm_sregs *sregs)
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static void __get_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
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{
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struct desc_ptr dt;
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vcpu_load(vcpu);
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kvm_get_segment(vcpu, &sregs->cs, VCPU_SREG_CS);
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kvm_get_segment(vcpu, &sregs->ds, VCPU_SREG_DS);
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kvm_get_segment(vcpu, &sregs->es, VCPU_SREG_ES);
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@ -7692,7 +7712,13 @@ int kvm_arch_vcpu_ioctl_get_sregs(struct kvm_vcpu *vcpu,
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if (vcpu->arch.interrupt.pending && !vcpu->arch.interrupt.soft)
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set_bit(vcpu->arch.interrupt.nr,
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(unsigned long *)sregs->interrupt_bitmap);
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}
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int kvm_arch_vcpu_ioctl_get_sregs(struct kvm_vcpu *vcpu,
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struct kvm_sregs *sregs)
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{
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vcpu_load(vcpu);
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__get_sregs(vcpu, sregs);
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vcpu_put(vcpu);
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return 0;
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}
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@ -7787,8 +7813,7 @@ int kvm_valid_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
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return 0;
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}
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int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
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struct kvm_sregs *sregs)
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static int __set_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
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{
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struct msr_data apic_base_msr;
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int mmu_reset_needed = 0;
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@ -7796,8 +7821,6 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
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struct desc_ptr dt;
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int ret = -EINVAL;
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vcpu_load(vcpu);
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if (!guest_cpuid_has(vcpu, X86_FEATURE_XSAVE) &&
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(sregs->cr4 & X86_CR4_OSXSAVE))
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goto out;
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@ -7876,6 +7899,16 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
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ret = 0;
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out:
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return ret;
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}
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int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
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struct kvm_sregs *sregs)
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{
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int ret;
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vcpu_load(vcpu);
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ret = __set_sregs(vcpu, sregs);
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vcpu_put(vcpu);
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return ret;
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}
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@ -8002,6 +8035,45 @@ int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
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return 0;
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}
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static void store_regs(struct kvm_vcpu *vcpu)
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{
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BUILD_BUG_ON(sizeof(struct kvm_sync_regs) > SYNC_REGS_SIZE_BYTES);
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if (vcpu->run->kvm_valid_regs & KVM_SYNC_X86_REGS)
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__get_regs(vcpu, &vcpu->run->s.regs.regs);
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if (vcpu->run->kvm_valid_regs & KVM_SYNC_X86_SREGS)
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__get_sregs(vcpu, &vcpu->run->s.regs.sregs);
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if (vcpu->run->kvm_valid_regs & KVM_SYNC_X86_EVENTS)
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kvm_vcpu_ioctl_x86_get_vcpu_events(
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vcpu, &vcpu->run->s.regs.events);
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}
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static int sync_regs(struct kvm_vcpu *vcpu)
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{
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if (vcpu->run->kvm_dirty_regs & ~KVM_SYNC_X86_VALID_FIELDS)
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return -EINVAL;
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if (vcpu->run->kvm_dirty_regs & KVM_SYNC_X86_REGS) {
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__set_regs(vcpu, &vcpu->run->s.regs.regs);
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vcpu->run->kvm_dirty_regs &= ~KVM_SYNC_X86_REGS;
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}
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if (vcpu->run->kvm_dirty_regs & KVM_SYNC_X86_SREGS) {
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if (__set_sregs(vcpu, &vcpu->run->s.regs.sregs))
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return -EINVAL;
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vcpu->run->kvm_dirty_regs &= ~KVM_SYNC_X86_SREGS;
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}
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if (vcpu->run->kvm_dirty_regs & KVM_SYNC_X86_EVENTS) {
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if (kvm_vcpu_ioctl_x86_set_vcpu_events(
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vcpu, &vcpu->run->s.regs.events))
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return -EINVAL;
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vcpu->run->kvm_dirty_regs &= ~KVM_SYNC_X86_EVENTS;
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}
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return 0;
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}
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static void fx_init(struct kvm_vcpu *vcpu)
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{
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fpstate_init(&vcpu->arch.guest_fpu.state);
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