linux-kernel - Re: [PATCHv2 2/3] x86/tdx: Fix race between set_memory_encrypted() and load_unaligned

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Date:   Fri, 2 Jun 2023 10:42:33 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.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>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCHv2 2/3] x86/tdx: Fix race between set_memory_encrypted()
 and load_unaligned_zeropad()

On 6/2/23 09:11, Michael Kelley (LINUX) wrote:
> Tom -- Does the above sequence *depend* on the hypervisor doing anything
> to make it work?  I'm not clear on why KVM would automatically change the
> page over to private.  If there's a dependency on the hypervisor doing
> something, then it seems like we'll need to standardize that "something"
> across hypervisors, lest we end up with per-hypervisor code in Linux to handle
> this scenario.  And running SEV-SNP with multiple VMPLs probably makes it
> even more complicated.
> 
> Kirill -- Same question about TDX.  Does making load_unaligned_zeropad()
> work in a TDX VM depend on the hypervisor doing anything?  Or is the
> behavior seen by the guest dependent only on architected behavior of
> the TDX processor?

No, there's no active help from the hypervisor here.

Also, fwiw, the "architected behavior" here is really just the TDX
module policy and _arguably_ the hardware Secure-EPT controlled by the
TDX module.