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

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Message-ID: <20230709060904.w3czdz23453eyx2h@box.shutemov.name>
Date:   Sun, 9 Jul 2023 09:09:04 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     "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>,
        "thomas.lendacky@....com" <thomas.lendacky@....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 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.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov