2018-02-06 8:32 GMT+08:00 Ken Hofsass <hofsass@xxxxxxxxxx>:
> Hi Wanpeng, that's disturbing! Could you give me more context? Did
> this occur while running part of the KVM unit tests? Does this happen
> every time? Do you know if this is this the first invocation of
> kvm_arch_vcpu_ioctl_set_sregs? When I ran against kvm-unit-tests
> w/qemu, I didn't hit this. Nor when I ran our other internal tests.
I just run a kvm guest (ubuntu 16.04 4.15-rc3) against kvm/queue w/
CONFIG_PREEMPT enabled.
Regards,
Wanpeng Li
> thanks,
> Ken Hofsass
>
>
> On Sun, Feb 4, 2018 at 5:29 PM, Wanpeng Li <kernellwp@xxxxxxxxx> wrote:
>> 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
>>>
