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

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Date:   Mon, 10 Jul 2023 14:17:28 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Tom Lendacky <thomas.lendacky@....com>,
        "Kirill A. Shutemov" <kirill@...temov.name>
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

From: Tom Lendacky <thomas.lendacky@....com> Sent: Monday, July 10, 2023 6:59 AM
> 
> 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...
> 

Yes, I'm still pursuing the RFC patch.  In addition to solving the SNP
problems, I think there are some benefits with TDX.  But I need to have
further discussion with Kirill, which may be delayed a bit while he's out
on vacation.

Michael