Re: [PATCH v1 4/6] KVM: x86: Add emulator helper for LASS violation check

[Zeng Guang <guang.zeng@intel.com>]

On 6/28/2023 2:28 AM, Sean Christopherson wrote:
> On Thu, Jun 01, 2023, Zeng Guang wrote:
>> When LASS is enabled, KVM need apply LASS violation check to instruction
>> emulations. Add helper for the usage of x86 emulator to perform LASS
>> protection.
>>
>> Signed-off-by: Zeng Guang <guang.zeng@intel.com>
>> Tested-by: Xuelian Guo <xuelian.guo@intel.com>
>> ---
>>   arch/x86/kvm/kvm_emulate.h |  1 +
>>   arch/x86/kvm/x86.c         | 12 ++++++++++++
>>   2 files changed, 13 insertions(+)
>>
>> diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
>> index f1439ab7c14b..fd1c2b22867e 100644
>> --- a/arch/x86/kvm/kvm_emulate.h
>> +++ b/arch/x86/kvm/kvm_emulate.h
>> @@ -230,6 +230,7 @@ struct x86_emulate_ops {
>>   	int (*leave_smm)(struct x86_emulate_ctxt *ctxt);
>>   	void (*triple_fault)(struct x86_emulate_ctxt *ctxt);
>>   	int (*set_xcr)(struct x86_emulate_ctxt *ctxt, u32 index, u64 xcr);
>> +	bool (*check_lass)(struct x86_emulate_ctxt *ctxt, u64 access, u64 la, u32 flags);
>>   };
>>   
>>   /* Type, address-of, and value of an instruction's operand. */
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index c0778ca39650..faf01fecc4ca 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -8287,6 +8287,17 @@ static void emulator_vm_bugged(struct x86_emulate_ctxt *ctxt)
>>   		kvm_vm_bugged(kvm);
>>   }
>>   
>> +static bool emulator_check_lass(struct x86_emulate_ctxt *ctxt,
>> +				u64 access, u64 la, u32 flags)
>> +{
>> +	struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
>> +
>> +	if (!is_long_mode(vcpu))
>> +		return false;
> Likely a moot point if we wrap ->gva_to_gpa(), but most this into the vendor
> implementation.
It's right way to move cpu mode check into is_lass_violation(). 
Previously I was struggling
to expect getting benefit from separate invocation. But it doesn't help 
much indeed.

>
> And if we keep these emulator hooks, massage the patch ordering:
>
>    1. Add plumbing to emulator to pass new flags
>    2. Add kvm_x86_ops definition and invocation from emulator
>    3. Implement and wire up vmx_is_lass_violation()
>
> That way the changes to each area of KVM are better isolated.
OK. Will reorganize the patch accordingly.
Thanks.
>> +	return static_call(kvm_x86_check_lass)(vcpu, access, la, flags);
>> +}
>> +
>>   static const struct x86_emulate_ops emulate_ops = {
>>   	.vm_bugged           = emulator_vm_bugged,
>>   	.read_gpr            = emulator_read_gpr,
>> @@ -8332,6 +8343,7 @@ static const struct x86_emulate_ops emulate_ops = {
>>   	.leave_smm           = emulator_leave_smm,
>>   	.triple_fault        = emulator_triple_fault,
>>   	.set_xcr             = emulator_set_xcr,
>> +	.check_lass          = emulator_check_lass,
>>   };
>>   
>>   static void toggle_interruptibility(struct kvm_vcpu *vcpu, u32 mask)
>> -- 
>> 2.27.0
>>