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Date:   Mon, 10 Jul 2023 08:59:04 -0500
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Subject: Re: [PATCHv3 0/3] x86/tdx: Fix one more load_unaligned_zeropad()
 issue
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To:     "Kirill A. Shutemov" <kirill@shutemov.name>,
        "Michael Kelley (LINUX)" <mikelley@microsoft.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        "dave.hansen@intel.com" <dave.hansen@intel.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
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        "bp@alien8.de" <bp@alien8.de>, Dexuan Cui <decui@microsoft.com>,
        "rick.p.edgecombe@intel.com" <rick.p.edgecombe@intel.com>,
        "sathyanarayanan.kuppuswamy@linux.intel.com" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        "seanjc@google.com" <seanjc@google.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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From:   Tom Lendacky <thomas.lendacky@amd.com>
In-Reply-To: <20230709060904.w3czdz23453eyx2h@box.shutemov.name>
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On 7/9/23 01:09, Kirill A. Shutemov wrote:
> On Sat, Jul 08, 2023 at 11:53:08PM +0000, Michael Kelley (LINUX) wrote:
>> From: Kirill A. Shutemov <kirill@shutemov.name> Sent: Friday, July 7, 2023 7:07 AM
>>>
>>> On Thu, Jul 06, 2023 at 04:48:32PM +0000, Michael Kelley (LINUX) wrote:
>>>> From: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Sent: Tuesday, June 6, 2023 2:56 AM
>>
>> [snip]
>>
>>>
>>> It only addresses the problem that happens on transition, but
>>> load_unaligned_zeropad() is still a problem for the shared mappings in
>>> general, after transition is complete. Like if load_unaligned_zeropad()
>>> steps from private to shared mapping and shared mapping triggers #VE,
>>> kernel should be able to handle it.
>>
>> I'm showing my ignorance of TDX architectural details, but what's the
>> situation where shared mappings in general can trigger a #VE?  How
>> do such situations get handled for references that aren't from
>> load_unaligned_zeropad()?
>>
> 
> Shared mappings are under host/VMM control. It can just not map the page
> in shared-ept and trigger ept-violation #VE.
> 
>>> Any comments?
>>
>> This looks good to me.  I applied the diff to a TDX VM running on
>> Hyper-V.  When a  load_unaligned_zeropad() occurs on a page that is
>> transitioning between private and shared, the zeropad fixup is now
>> done correctly via the #VE handler.  (This is *without* my RFC patch to
>> mark the pages invalid during a transition.)
> 
> Great.
> 
> I am at vacation for the next two weeks. I will prepare a proper patch
> when I am back. Feel free to make patch yourself if you feel it is urgent.
> 

Michael,

Are you still pursuing the RFC patch, then? Just trying to decide whether 
a patch will be needed for SNP...

Thanks,
Tom