linux-kernel - Re: [PATCH 5/8] KVM: SVM: Re-inject INT3/INTO instead of retrying the instruction

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Message-ID: <a3cf781b-0b1a-0bba-6b37-12666c7fc154@maciej.szmigiero.name>
Date:   Mon, 4 Apr 2022 18:53:16 +0200
From:   "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Maxim Levitsky <mlevitsk@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/8] KVM: SVM: Re-inject INT3/INTO instead of retrying the
 instruction

>>> index 47e7427d0395..a770a1c7ddd2 100644
>>> --- a/arch/x86/kvm/svm/svm.h
>>> +++ b/arch/x86/kvm/svm/svm.h
>>> @@ -230,8 +230,8 @@ struct vcpu_svm {
>>>   	bool nmi_singlestep;
>>>   	u64 nmi_singlestep_guest_rflags;
>>>   
>>> -	unsigned int3_injected;
>>> -	unsigned long int3_rip;
>>> +	unsigned soft_int_injected;
>>> +	unsigned long soft_int_linear_rip;
>>>   
>>>   	/* optional nested SVM features that are enabled for this guest  */
>>>   	bool nrips_enabled                : 1;
>>
>>
>> I mostly agree with this patch, but think that it doesn't address the
>> original issue that Maciej wanted to address:
>>
>> Suppose that there is *no* instruction in L2 code which caused the software
>> exception, but rather L1 set arbitrary next_rip, and set EVENTINJ to software
>> exception with some vector, and that injection got interrupted.
>>
>> I don't think that this code will support this.
> 
> Argh, you're right.  Maciej's selftest injects without an instruction, but it doesn't
> configure the scenario where that injection fails due to an exception+VM-Exit that
> isn't intercepted by L1 and is handled by L0.  The event_inj test gets the coverage
> for the latter, but always has a backing instruction.

Still reviewing the whole patch set, but want to clear this point quickly:
The selftest does have an implicit intervening NPF (handled by L0) while
injecting the first L1 -> L2 event.

Thanks,
Maciej