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Date:   Sat, 16 Oct 2021 20:49:34 -0700
From:   Sathyanarayanan Kuppuswamy 
To:     Dave Hansen <>,
        Thomas Gleixner <>,
        Ingo Molnar <>, Borislav Petkov <>,, Paolo Bonzini <>,
        David Hildenbrand <>,
        Andrea Arcangeli <>,
        Josh Poimboeuf <>,
        Juergen Gross <>, Deep Shah <>,
        VMware Inc <>,
        Vitaly Kuznetsov <>,
        Wanpeng Li <>,
        Jim Mattson <>,
        Joerg Roedel <>
Cc:     Peter H Anvin <>, Tony Luck <>,
        Dan Williams <>,
        Andi Kleen <>,
        Kirill Shutemov <>,
        Sean Christopherson <>,
        Kuppuswamy Sathyanarayanan <>,
Subject: Re: [PATCH v10 06/11] x86/traps: Add #VE support for TDX guest

On 10/16/21 8:18 PM, Dave Hansen wrote:
> On 10/16/21 7:45 PM, Sathyanarayanan Kuppuswamy wrote:
>>>> +bool tdx_get_ve_info(struct ve_info *ve)
>>>> +{
>>>> +    struct tdx_module_output out;
>>>> +    u64 ret;
>>>> +
>>>> +    if (!ve)
>>>> +        return false;
>>> This should be WARN_ON_ONCE() if at all.
>> This is an input validation. Since we need to de-reference "ve" in
>> the following code, we want to validate it to avoid NULL pointer
>> exception. As per current usage of this function, "ve" will not be
>> NULL. But we have added this check as a extra precaution against
>> future use cases.
> Input validation, eh?
> It's one thing if this argument comes from userspace, or is even open
> for modules to call.  You *might* have an argument that it should be
> checked in case something in the kernel goes insane.
> But, there's a single call site.  It looks like this:

As per current use cases (exc_virtualization_exception() &
tdx_early_handle_ve()), it will never happen. As I have mentioned,
it was added as a precaution against the future use case or any
misuse of this function in kernel. We did not have this check
initially. But was added later due to review suggestion.

But I am fine with removing it if it is required.

>> +DEFINE_IDTENTRY(exc_virtualization_exception)
>> +{
>> +	struct ve_info ve;
> ...
>> +	ret = tdx_get_ve_info(&ve);
> Could you please explain, given the existing kernel code, how !ve could
> ever possibly happen?  Or, how tdx_get_ve_info() might conceivably ever
> be called from another path which is not extremely well controlled?

Sathyanarayanan Kuppuswamy
Linux Kernel Developer

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