linux-kernel - Re: [PATCHv3 0/3] x86/tdx: Fix one more load_unaligned

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Message-ID: <fa869adb-a873-5f40-d843-73cc7e3a58cf@amd.com>
Date:   Mon, 10 Jul 2023 08:59:04 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "dave.hansen@...el.com" <dave.hansen@...el.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, Dexuan Cui <decui@...rosoft.com>,
        "rick.p.edgecombe@...el.com" <rick.p.edgecombe@...el.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv3 0/3] x86/tdx: Fix one more load_unaligned_zeropad()
 issue

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@...temov.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@...ux.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