From: Wanpeng Li <[email protected]>
This can be reproduced by EPT=1, unrestricted_guest=N, emulate_invalid_state=Y
or EPT=0, the trace of kvm-unit-tests/taskswitch2.flat is like below, it tries
to emulate invalid guest state task-switch:
kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0
kvm_emulate_insn: 42000:0:0f 0b (0x2)
kvm_emulate_insn: 42000:0:0f 0b (0x2) failed
kvm_inj_exception: #UD (0x0)
kvm_entry: vcpu 0
kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0
kvm_emulate_insn: 42000:0:0f 0b (0x2)
kvm_emulate_insn: 42000:0:0f 0b (0x2) failed
kvm_inj_exception: #UD (0x0)
......................
It appears that the task-switch emulation updates rflags (and vm86
flag) only after the segments are loaded, causing vmx->emulation_required
to be set, when in fact invalid guest state emulation is not needed.
This patch fixes it by updating vmx->emulation_required after the
rflags (and vm86 flag) is updated in task-switch emulation.
Thanks Radim for moving the update to vmx__set_flags and adding Paolo's
suggestion for the check.
Suggested-by: Nadav Amit <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Radim Krčmář <[email protected]>
Cc: Nadav Amit <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
---
arch/x86/kvm/vmx.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 84e62ac..287639e 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2326,6 +2326,11 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
__vmx_load_host_state(to_vmx(vcpu));
}
+static bool emulation_required(struct kvm_vcpu *vcpu)
+{
+ return emulate_invalid_guest_state && !guest_state_valid(vcpu);
+}
+
static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu);
/*
@@ -2363,6 +2368,9 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
{
+ unsigned long old_rflags = vmx_get_rflags(vcpu);
+ unsigned long save_rflags = rflags;
+
__set_bit(VCPU_EXREG_RFLAGS, (ulong *)&vcpu->arch.regs_avail);
to_vmx(vcpu)->rflags = rflags;
if (to_vmx(vcpu)->rmode.vm86_active) {
@@ -2370,6 +2378,9 @@ static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
rflags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM;
}
vmcs_writel(GUEST_RFLAGS, rflags);
+
+ if ((old_rflags ^ save_rflags) & X86_EFLAGS_VM)
+ to_vmx(vcpu)->emulation_required = emulation_required(vcpu);
}
static u32 vmx_get_pkru(struct kvm_vcpu *vcpu)
@@ -3857,11 +3868,6 @@ static __init int alloc_kvm_area(void)
return 0;
}
-static bool emulation_required(struct kvm_vcpu *vcpu)
-{
- return emulate_invalid_guest_state && !guest_state_valid(vcpu);
-}
-
static void fix_pmode_seg(struct kvm_vcpu *vcpu, int seg,
struct kvm_segment *save)
{
--
2.7.4
2017-07-19 16:40-0700, Wanpeng Li:
> From: Wanpeng Li <[email protected]>
>
> This can be reproduced by EPT=1, unrestricted_guest=N, emulate_invalid_state=Y
> or EPT=0, the trace of kvm-unit-tests/taskswitch2.flat is like below, it tries
> to emulate invalid guest state task-switch:
>
> kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0
> kvm_emulate_insn: 42000:0:0f 0b (0x2)
> kvm_emulate_insn: 42000:0:0f 0b (0x2) failed
> kvm_inj_exception: #UD (0x0)
> kvm_entry: vcpu 0
> kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0
> kvm_emulate_insn: 42000:0:0f 0b (0x2)
> kvm_emulate_insn: 42000:0:0f 0b (0x2) failed
> kvm_inj_exception: #UD (0x0)
> ......................
>
> It appears that the task-switch emulation updates rflags (and vm86
> flag) only after the segments are loaded, causing vmx->emulation_required
> to be set, when in fact invalid guest state emulation is not needed.
>
> This patch fixes it by updating vmx->emulation_required after the
> rflags (and vm86 flag) is updated in task-switch emulation.
>
> Thanks Radim for moving the update to vmx__set_flags and adding Paolo's
> suggestion for the check.
>
> Suggested-by: Nadav Amit <[email protected]>
> Cc: Paolo Bonzini <[email protected]>
> Cc: Radim Krčmář <[email protected]>
> Cc: Nadav Amit <[email protected]>
> Signed-off-by: Wanpeng Li <[email protected]>
> ---
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
> {
> + unsigned long old_rflags = vmx_get_rflags(vcpu);
> + unsigned long save_rflags = rflags;
> +
> __set_bit(VCPU_EXREG_RFLAGS, (ulong *)&vcpu->arch.regs_avail);
> to_vmx(vcpu)->rflags = rflags;
> if (to_vmx(vcpu)->rmode.vm86_active) {
> @@ -2370,6 +2378,9 @@ static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
> rflags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM;
> }
> vmcs_writel(GUEST_RFLAGS, rflags);
> +
> + if ((old_rflags ^ save_rflags) & X86_EFLAGS_VM)
Looks good, thanks to both.
The desired rflags are saved in to_vmx(vcpu)->rflags, so we don't need
the temporary variable -- would using that or vmx_get_rflags(vcpu)
generate worse code?
2017-07-20 15:57 GMT+08:00 Radim Krčmář <[email protected]>:
> 2017-07-19 16:40-0700, Wanpeng Li:
>> From: Wanpeng Li <[email protected]>
>>
>> This can be reproduced by EPT=1, unrestricted_guest=N, emulate_invalid_state=Y
>> or EPT=0, the trace of kvm-unit-tests/taskswitch2.flat is like below, it tries
>> to emulate invalid guest state task-switch:
>>
>> kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0
>> kvm_emulate_insn: 42000:0:0f 0b (0x2)
>> kvm_emulate_insn: 42000:0:0f 0b (0x2) failed
>> kvm_inj_exception: #UD (0x0)
>> kvm_entry: vcpu 0
>> kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0
>> kvm_emulate_insn: 42000:0:0f 0b (0x2)
>> kvm_emulate_insn: 42000:0:0f 0b (0x2) failed
>> kvm_inj_exception: #UD (0x0)
>> ......................
>>
>> It appears that the task-switch emulation updates rflags (and vm86
>> flag) only after the segments are loaded, causing vmx->emulation_required
>> to be set, when in fact invalid guest state emulation is not needed.
>>
>> This patch fixes it by updating vmx->emulation_required after the
>> rflags (and vm86 flag) is updated in task-switch emulation.
>>
>> Thanks Radim for moving the update to vmx__set_flags and adding Paolo's
>> suggestion for the check.
>>
>> Suggested-by: Nadav Amit <[email protected]>
>> Cc: Paolo Bonzini <[email protected]>
>> Cc: Radim Krčmář <[email protected]>
>> Cc: Nadav Amit <[email protected]>
>> Signed-off-by: Wanpeng Li <[email protected]>
>> ---
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>> {
>> + unsigned long old_rflags = vmx_get_rflags(vcpu);
>> + unsigned long save_rflags = rflags;
>> +
>> __set_bit(VCPU_EXREG_RFLAGS, (ulong *)&vcpu->arch.regs_avail);
>> to_vmx(vcpu)->rflags = rflags;
>> if (to_vmx(vcpu)->rmode.vm86_active) {
>> @@ -2370,6 +2378,9 @@ static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>> rflags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM;
>> }
>> vmcs_writel(GUEST_RFLAGS, rflags);
>> +
>> + if ((old_rflags ^ save_rflags) & X86_EFLAGS_VM)
>
> Looks good, thanks to both.
>
> The desired rflags are saved in to_vmx(vcpu)->rflags, so we don't need
> the temporary variable -- would using that or vmx_get_rflags(vcpu)
> generate worse code?
Yeah, I will send out a newer version.
Regards,
Wanpeng Li