linux-kernel - Re: [PATCH 2/4] x86/tdx: Use ReportFatalError to report missing SEPT_VE

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Message-ID: <795d6e1d-c79c-b079-3412-69ca2f8ee874@intel.com>
Date:   Thu, 15 Dec 2022 10:18:24 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Elena Reshetova <elena.reshetova@...el.com>, x86@...nel.org,
        linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] x86/tdx: Use ReportFatalError to report missing
 SEPT_VE_DISABLE

On 12/15/22 09:12, Kirill A. Shutemov wrote:
>> Getting *all* users of panic this magic ability would be a lot better
>> than giving it to one call-site of panic().
>>
>> I'm all for making the panic() path as short and simple as possible, but
>> it would be nice if this fancy hypercall would get used in more than one
>> spot.
> Well, I don't see an obvious way to integrate this into panic().
> 
> There is panic_notifier_list and it kinda/sorta works, see the patch
> below.
> 
> But it breaks panic_notifier_list contract: the callback will never return
> and no other callback will be able to do their stuff. panic_timeout is
> also broken.
> 
> So ReportFatalError() is no good for the task. And I don't have anything
> else :/

Do we *really* have to do a hard stop when SEPT_VE_DISABLE is missing?

Wouldn't it be simpler to just defer the check until we can spit out a
sane error message about it?

Or is there too much security exposure by continuing?