linux-kernel - Re: [RFC v2-fix-v3 1/1] x86/tdx: Skip WBINVD instruction for TDX guest

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Date:   Tue, 8 Jun 2021 16:04:46 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC v2-fix-v3 1/1] x86/tdx: Skip WBINVD instruction for TDX
 guest



On 6/8/21 3:53 PM, Dave Hansen wrote:
> On 6/8/21 3:36 PM, Kuppuswamy, Sathyanarayanan wrote:
>> On 6/8/21 3:17 PM, Dave Hansen wrote:
>>> On 6/8/21 2:35 PM, Kuppuswamy Sathyanarayanan wrote:

> 
> A kernel driver using WBINVD will "sigfault"?  I'm not sure what that
> means.  How does the kernel "sigfault"?

Sorry, un-supported #VE is handled similar to #GP fault.

> 
>> In this patch we only create exception for ACPI sleep driver code. If
>> commit log is confusing, I can remove information about other unsupported
>> feature (with WBINVD usage).
> 
> Yes, the changelog is horribly confusing.  But simply removing this
> information is insufficient to rectify the deficiency.

I will remove all the unrelated information from this commit log. As long as
commit log *only* talks and handles the exception for ACPI sleep driver, it
should be acceptable for you right? I will also add a note about, if any
other feature with WBINVD usage is enabled, it would lead to #GP fault.

> 
> I've lost trust that due diligence will be performed on this series on
> its own.  I've seen too many broken promises and too many holes.
> 
> Here's what I want to see: a list of all of the unique call sites for
> WBINVD in the kernel.  I want a written down methodology for how the
> list of call sites was generated.  I want to see an item-by-item list of
> why those call sites are unreachable with the TDX guest code.  It might
> be because they've been patched in this patch, or the driver has been
> disabled, or because the TDX architecture spec would somehow prohibit
> the situation where it might be needed.  But, there needs to be a list,
> and you have to show your work.  If you refer to code from this series
> as helping to prevent WBINVD, then it has to be earlier in this series,
> not in some other series and not later in this series.
> 
> Just eyeballing it, there are ~50 places in the kernel that need auditing.
> 
> Right now, we mostly have indiscriminate hand-waving about this not
> being a problem.  It's a hard NAK from me on this patch until this audit
> is in place.
> 

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer