linux-kernel - Re: [PATCH v8 06/11] x86/traps: Add #VE support for TDX guest

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Date:   Sun, 17 Oct 2021 10:15:22 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Borislav Petkov <bp@...en8.de>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>, Deep Shah <sdeep@...are.com>,
        VMware Inc <pv-drivers@...are.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, Peter H Anvin <hpa@...or.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 06/11] x86/traps: Add #VE support for TDX guest

On 10/7/21 10:06 AM, Borislav Petkov wrote:
> On Mon, Oct 04, 2021 at 07:52:00PM -0700, Kuppuswamy Sathyanarayanan wrote:
>> +unsigned long tdx_get_ve_info(struct ve_info *ve)
>> +{
>> +	struct tdx_module_output out = {0};
>> +	u64 ret;
>> +
>> +	/*
>> +	 * NMIs and machine checks are suppressed. Before this point any
>> +	 * #VE is fatal. After this point (TDGETVEINFO call), NMIs and
>> +	 * additional #VEs are permitted (but it is expected not to
>> +	 * happen unless kernel panics).
>> +	 */
>> +	ret = __tdx_module_call(TDGETVEINFO, 0, 0, 0, 0, &out);
> Same question as before - why do you need to clear this @out thing above
> when __tdx_module_call() will overwrite it?
> 
> What you should do instead is check that @ve pointer which you get
> passed in - it might be NULL.

Hi Borislav,

That ve_info really is specific to handling a fault.  There's only one
call site:

> +DEFINE_IDTENTRY(exc_virtualization_exception)
> +{
> +	struct ve_info ve;
...
> +	ret = tdx_get_ve_info(&ve);

I think it's equivalent to something like a 'pt_regs' or 'stack_info'
that we pass around in other exception handlers.  It's always stack
allocated.  It's never dynamically allocated and NULL is never passed
for some other semantic reason.