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

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Message-ID: <4f04c6c0-31c6-9293-25c1-ea4bc1722dc8@intel.com>
Date:   Mon, 18 Oct 2021 07:05:21 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        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 10/18/21 3:53 AM, Borislav Petkov wrote:
> On Sun, Oct 17, 2021 at 10:15:22AM -0700, Dave Hansen wrote:
>> 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.
> Ok, but why is adding that check such a big deal?

It's really not a big deal.

> Are you saying that nothing else will call tdx_get_ve_info() in the
> future so we should trust the passed in *ve pointer blindly or should we
> simply add that cheap check just in case.
> 
> I don't mind having it without it but wondering why a little defensive
> programming is a problem, at all.

It's not a problem.  I think I'd just rather see a splat (oops or
WARN_ON_ONCE()) than silently returning an error.