linux-kernel - Re: [PATCH 1/3] KVM: x86, vmx: Add function for event delivery error generation

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Message-ID: <cea2040f-7214-41cb-9e9c-98895bf5a1ec@gmail.com>
Date: Wed, 16 Oct 2024 23:05:04 +0100
From: Ivan Orlov <ivan.orlov0322@...il.com>
To: Sean Christopherson <seanjc@...gle.com>, Ivan Orlov <iorlov@...zon.com>
Cc: bp@...en8.de, dave.hansen@...ux.intel.com, mingo@...hat.com,
 pbonzini@...hat.com, shuah@...nel.org, tglx@...utronix.de, hpa@...or.com,
 kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org, x86@...nel.org, jalliste@...zon.com,
 nh-open-source@...zon.com, pdurrant@...zon.co.uk
Subject: Re: [PATCH 1/3] KVM: x86, vmx: Add function for event delivery error
 generation

On 10/16/24 22:05, Sean Christopherson wrote:
> On Tue, Oct 15, 2024, Ivan Orlov wrote:
>>>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>>>> index c67e448c6ebd..afd785e7f3a3 100644
>>>> --- a/arch/x86/kvm/vmx/vmx.c
>>>> +++ b/arch/x86/kvm/vmx/vmx.c
>>>> @@ -6550,19 +6550,10 @@ static int __vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
>>>>   	     exit_reason.basic != EXIT_REASON_APIC_ACCESS &&
>>>>   	     exit_reason.basic != EXIT_REASON_TASK_SWITCH &&
>>>>   	     exit_reason.basic != EXIT_REASON_NOTIFY)) {
>>>> -		int ndata = 3;
>>>> +		gpa_t gpa = vmcs_read64(GUEST_PHYSICAL_ADDRESS);
>>>> +		bool is_mmio = exit_reason.basic == EXIT_REASON_EPT_MISCONFIG;
>>>
>>> There's no need for is_mmio, just pass INVALID_GPA when the GPA isn't known.
>>
>> Ah alright, then we definitely don't need an is_mmio field. I assume we
>> can't do MMIO at GPA=0, right?
> 
> Wrong :-)
> 

Then getting rid of `is_mmio` will make distinguishing between vectoring 
error due to MMIO with GPA=0 and non-mmio vectoring error quite hard for 
the error reporti

Passing INVALID_GPA into the userspace due to non-mmio vectoring error 
will change the existing internal.data order, but I can do it if it's 
fine. Sorry for nitpicking :)

>  From an architectural perspective, GPA=0 is not special in any way.  E.g. prior
> to L1TF, Linux would happily use the page with PFN=0.
> 

Cool, didn't know about this vulnerability... Thanks for the explanation!

-- 
Kind regards,
Ivan Orlov