2018-02-01 8:03 GMT+08:00 Ken Hofsass <hofsass@xxxxxxxxxx>:
> 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@xxxxxxxxxx>
This commit in kvm/queue results in:
general protection fault: 0000 [#1] PREEMPT SMP PTI
CPU: 7 PID: 2348 Comm: qemu-system-x86 Not tainted 4.15.0+ #4
Hardware name: LENOVO ThinkCentre M8500t-N000/SHARKBAY, BIOS
FBKTC1AUS 02/16/2016
RIP: 0010:preempt_notifier_unregister+0x13/0x40
RSP: 0018:ffffbe6541c07da8 EFLAGS: 00010286
RAX: dead000000000100 RBX: ffff99ed46ca8000 RCX: 0000000037271e7b
RDX: dead000000000200 RSI: 0000000000000000 RDI: ffff99ed46ca8008
RBP: ffffbe6541c07da8 R08: 00000000fe0913b4 R09: 442c1f7a00000000
R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000000
R13: ffff99ed46ca8000 R14: ffff99ed46ca8058 R15: ffff99ed47635400
FS: 00007f3c2b474700(0000) GS:ffff99ed8e200000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f3c1c001000 CR3: 00000003c73f4006 CR4: 00000000001626e0
Call Trace:
vcpu_put+0x28/0x50 [kvm]
kvm_arch_vcpu_ioctl_set_sregs+0x2d/0x40 [kvm]
kvm_vcpu_ioctl+0x54a/0x720 [kvm]
? __fget+0xfc/0x210
? __fget+0xfc/0x210
do_vfs_ioctl+0xa4/0x6a0
? __fget+0x11d/0x210
SyS_ioctl+0x79/0x90
entry_SYSCALL_64_fastpath+0x25/0x9c
RIP: 0033:0x7f3c36fd0f47
RSP: 002b:00007f3c2b473668 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000555a11f78c10 RCX: 00007f3c36fd0f47
RDX: 00007f3c2b473710 RSI: 000000004138ae84 RDI: 000000000000000f
RBP: 0000000000000003 R08: 0000555a107825b0 R09: 00007f3c1c001000
R10: 00007f3c1c003010 R11: 0000000000000246 R12: 00007f3c2b473870
R13: 00007f3c1c001000 R14: 00007f3c2b4749c0 R15: 0000555a11f78c10
RIP: preempt_notifier_unregister+0x13/0x40 RSP: ffffbe6541c07da8
---[ end trace 318a26af2b7ef2bc ]---
Regards,
Wanpeng Li
> ---
> Documentation/virtual/kvm/api.txt | 40 ++++++++++++++
> arch/x86/include/uapi/asm/kvm.h | 19 ++++++-
> arch/x86/kvm/x86.c | 108 +++++++++++++++++++++++++++++++++-----
> 3 files changed, 152 insertions(+), 15 deletions(-)
>
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index de55fe173afe..97bc2d0e69aa 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -4014,6 +4014,46 @@ Once this is done the KVM_REG_MIPS_VEC_* and KVM_REG_MIPS_MSA_* registers can be
> accessed, and the Config5.MSAEn bit is accessible via the KVM API and also from
> the guest.
>
> +6.74 KVM_CAP_SYNC_REGS
> +Architectures: s390, x86
> +Target: s390: always enabled, x86: vcpu
> +Parameters: none
> +Returns: x86: KVM_CHECK_EXTENSION returns a bit-array indicating which register
> +sets are supported (bitfields defined in arch/x86/include/uapi/asm/kvm.h).
> +
> +As described above in the kvm_sync_regs struct info in section 5 (kvm_run):
> +KVM_CAP_SYNC_REGS "allow[s] userspace to access certain guest registers
> +without having to call SET/GET_*REGS". This reduces overhead by eliminating
> +repeated ioctl calls for setting and/or getting register values. This is
> +particularly important when userspace is making synchronous guest state
> +modifications, e.g. when emulating and/or intercepting instructions in
> +userspace.
> +
> +For s390 specifics, please refer to the source code.
> +
> +For x86:
> +- the register sets to be copied out to kvm_run are selectable
> + by userspace (rather that all sets being copied out for every exit).
> +- vcpu_events are available in addition to regs and sregs.
> +
> +For x86, the 'kvm_valid_regs' field of struct kvm_run is overloaded to
> +function as an input bit-array field set by userspace to indicate the
> +specific register sets to be copied out on the next exit.
> +
> +To indicate when userspace has modified values that should be copied into
> +the vCPU, the all architecture bitarray field, 'kvm_dirty_regs' must be set.
> +This is done using the same bitflags as for the 'kvm_valid_regs' field.
> +If the dirty bit is not set, then the register set values will not be copied
> +into the vCPU even if they've been modified.
> +
> +Unused bitfields in the bitarrays must be set to zero.
> +
> +struct kvm_sync_regs {
> + struct kvm_regs regs;
> + struct kvm_sregs sregs;
> + struct kvm_vcpu_events events;
> +};
> +
> 7. Capabilities that can be enabled on VMs
> ------------------------------------------
>
> diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
> index f3a960488eae..c535c2fdea13 100644
> --- a/arch/x86/include/uapi/asm/kvm.h
> +++ b/arch/x86/include/uapi/asm/kvm.h
> @@ -354,8 +354,25 @@ struct kvm_xcrs {
> __u64 padding[16];
> };
>
> -/* definition of registers in kvm_run */
> +#define KVM_SYNC_X86_REGS (1UL << 0)
> +#define KVM_SYNC_X86_SREGS (1UL << 1)
> +#define KVM_SYNC_X86_EVENTS (1UL << 2)
> +
> +#define KVM_SYNC_X86_VALID_FIELDS \
> + (KVM_SYNC_X86_REGS| \
> + KVM_SYNC_X86_SREGS| \
> + KVM_SYNC_X86_EVENTS)
> +
> +/* kvm_sync_regs struct included by kvm_run struct */
> struct kvm_sync_regs {
> + /* Members of this structure are potentially malicious.
> + * Care must be taken by code reading, esp. interpreting,
> + * data fields from them inside KVM to prevent TOCTOU and
> + * double-fetch types of vulnerabilities.
> + */
> + struct kvm_regs regs;
> + struct kvm_sregs sregs;
> + struct kvm_vcpu_events events;
> };
>
> #define KVM_X86_QUIRK_LINT0_REENABLED (1 << 0)
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 0204b2b8a293..ffd2c4e5d245 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -100,6 +100,9 @@ static void update_cr8_intercept(struct kvm_vcpu *vcpu);
> static void process_nmi(struct kvm_vcpu *vcpu);
> static void enter_smm(struct kvm_vcpu *vcpu);
> static void __kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags);
> +static void store_regs(struct kvm_vcpu *vcpu);
> +static int sync_regs(struct kvm_vcpu *vcpu);
> +static int check_valid_regs(struct kvm_vcpu *vcpu);
>
> struct kvm_x86_ops *kvm_x86_ops __read_mostly;
> EXPORT_SYMBOL_GPL(kvm_x86_ops);
> @@ -2743,6 +2746,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> case KVM_CAP_IMMEDIATE_EXIT:
> r = 1;
> break;
> + case KVM_CAP_SYNC_REGS:
> + r = KVM_SYNC_X86_VALID_FIELDS;
> + break;
> case KVM_CAP_ADJUST_CLOCK:
> r = KVM_CLOCK_TSC_STABLE;
> break;
> @@ -7325,6 +7331,12 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
> return 0;
> }
>
> +static int check_valid_regs(struct kvm_vcpu *vcpu)
> +{
> + if (vcpu->run->kvm_valid_regs & ~KVM_SYNC_X86_VALID_FIELDS)
> + return -EINVAL;
> + return 0;
> +}
>
> int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
> {
> @@ -7351,6 +7363,17 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
> goto out;
> }
>
> + if (vcpu->run->kvm_valid_regs) {
> + r = check_valid_regs(vcpu);
> + if (r != 0)
> + goto out;
> + }
> + if (vcpu->run->kvm_dirty_regs) {
> + r = sync_regs(vcpu);
> + if (r != 0)
> + goto out;
> + }
> +
> /* re-sync apic's tpr */
> if (!lapic_in_kernel(vcpu)) {
> if (kvm_set_cr8(vcpu, kvm_run->cr8) != 0) {
> @@ -7375,6 +7398,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>
> out:
> kvm_put_guest_fpu(vcpu);
> + if (vcpu->run->kvm_valid_regs)
> + store_regs(vcpu);
> post_kvm_run_save(vcpu);
> kvm_sigset_deactivate(vcpu);
>
> @@ -7382,10 +7407,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
> return r;
> }
>
> -int kvm_arch_vcpu_ioctl_get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
> +static void __get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
> {
> - vcpu_load(vcpu);
> -
> if (vcpu->arch.emulate_regs_need_sync_to_vcpu) {
> /*
> * We are here if userspace calls get_regs() in the middle of
> @@ -7418,15 +7441,18 @@ int kvm_arch_vcpu_ioctl_get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
>
> regs->rip = kvm_rip_read(vcpu);
> regs->rflags = kvm_get_rflags(vcpu);
> +}
>
> +int kvm_arch_vcpu_ioctl_get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
> +{
> + vcpu_load(vcpu);
> + __get_regs(vcpu, regs);
> vcpu_put(vcpu);
> return 0;
> }
>
> -int kvm_arch_vcpu_ioctl_set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
> +static void __set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
> {
> - vcpu_load(vcpu);
> -
> vcpu->arch.emulate_regs_need_sync_from_vcpu = true;
> vcpu->arch.emulate_regs_need_sync_to_vcpu = false;
>
> @@ -7455,7 +7481,12 @@ int kvm_arch_vcpu_ioctl_set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
> vcpu->arch.exception.pending = false;
>
> kvm_make_request(KVM_REQ_EVENT, vcpu);
> +}
>
> +int kvm_arch_vcpu_ioctl_set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
> +{
> + vcpu_load(vcpu);
> + __set_regs(vcpu, regs);
> vcpu_put(vcpu);
> return 0;
> }
> @@ -7470,13 +7501,10 @@ void kvm_get_cs_db_l_bits(struct kvm_vcpu *vcpu, int *db, int *l)
> }
> EXPORT_SYMBOL_GPL(kvm_get_cs_db_l_bits);
>
> -int kvm_arch_vcpu_ioctl_get_sregs(struct kvm_vcpu *vcpu,
> - struct kvm_sregs *sregs)
> +static void __get_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
> {
> struct desc_ptr dt;
>
> - vcpu_load(vcpu);
> -
> kvm_get_segment(vcpu, &sregs->cs, VCPU_SREG_CS);
> kvm_get_segment(vcpu, &sregs->ds, VCPU_SREG_DS);
> kvm_get_segment(vcpu, &sregs->es, VCPU_SREG_ES);
> @@ -7507,7 +7535,13 @@ int kvm_arch_vcpu_ioctl_get_sregs(struct kvm_vcpu *vcpu,
> if (vcpu->arch.interrupt.pending && !vcpu->arch.interrupt.soft)
> set_bit(vcpu->arch.interrupt.nr,
> (unsigned long *)sregs->interrupt_bitmap);
> +}
>
> +int kvm_arch_vcpu_ioctl_get_sregs(struct kvm_vcpu *vcpu,
> + struct kvm_sregs *sregs)
> +{
> + vcpu_load(vcpu);
> + __get_sregs(vcpu, sregs);
> vcpu_put(vcpu);
> return 0;
> }
> @@ -7579,8 +7613,7 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int idt_index,
> }
> EXPORT_SYMBOL_GPL(kvm_task_switch);
>
> -int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
> - struct kvm_sregs *sregs)
> +static int __set_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
> {
> struct msr_data apic_base_msr;
> int mmu_reset_needed = 0;
> @@ -7588,8 +7621,6 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
> struct desc_ptr dt;
> int ret = -EINVAL;
>
> - vcpu_load(vcpu);
> -
> if (!guest_cpuid_has(vcpu, X86_FEATURE_XSAVE) &&
> (sregs->cr4 & X86_CR4_OSXSAVE))
> goto out;
> @@ -7665,6 +7696,16 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
>
> ret = 0;
> out:
> + return ret;
> +}
> +
> +int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
> + struct kvm_sregs *sregs)
> +{
> + int ret;
> +
> + vcpu_load(vcpu);
> + ret = __set_sregs(vcpu, sregs);
> vcpu_put(vcpu);
> return ret;
> }
> @@ -7791,6 +7832,45 @@ int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
> return 0;
> }
>
> +static void store_regs(struct kvm_vcpu *vcpu)
> +{
> + BUILD_BUG_ON(sizeof(struct kvm_sync_regs) > SYNC_REGS_SIZE_BYTES);
> +
> + if (vcpu->run->kvm_valid_regs & KVM_SYNC_X86_REGS)
> + __get_regs(vcpu, &vcpu->run->s.regs.regs);
> +
> + if (vcpu->run->kvm_valid_regs & KVM_SYNC_X86_SREGS)
> + __get_sregs(vcpu, &vcpu->run->s.regs.sregs);
> +
> + if (vcpu->run->kvm_valid_regs & KVM_SYNC_X86_EVENTS)
> + kvm_vcpu_ioctl_x86_get_vcpu_events(
> + vcpu, &vcpu->run->s.regs.events);
> +}
> +
> +static int sync_regs(struct kvm_vcpu *vcpu)
> +{
> + if (vcpu->run->kvm_dirty_regs & ~KVM_SYNC_X86_VALID_FIELDS)
> + return -EINVAL;
> +
> + if (vcpu->run->kvm_dirty_regs & KVM_SYNC_X86_REGS) {
> + __set_regs(vcpu, &vcpu->run->s.regs.regs);
> + vcpu->run->kvm_dirty_regs &= ~KVM_SYNC_X86_REGS;
> + }
> + if (vcpu->run->kvm_dirty_regs & KVM_SYNC_X86_SREGS) {
> + if (__set_sregs(vcpu, &vcpu->run->s.regs.sregs))
> + return -EINVAL;
> + vcpu->run->kvm_dirty_regs &= ~KVM_SYNC_X86_SREGS;
> + }
> + if (vcpu->run->kvm_dirty_regs & KVM_SYNC_X86_EVENTS) {
> + if (kvm_vcpu_ioctl_x86_set_vcpu_events(
> + vcpu, &vcpu->run->s.regs.events))
> + return -EINVAL;
> + vcpu->run->kvm_dirty_regs &= ~KVM_SYNC_X86_EVENTS;
> + }
> +
> + return 0;
> +}
> +
> static void fx_init(struct kvm_vcpu *vcpu)
> {
> fpstate_init(&vcpu->arch.guest_fpu.state);
> --
> 2.16.0.rc1.238.g530d649a79-goog
>
