linux-kernel - Re: [PATCH] x86/mm/cpa: Warn if set_memory

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Date:   Thu, 26 Oct 2023 01:45:15 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "Lutomirski, Andy" <luto@...nel.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "Reshetova, Elena" <elena.reshetova@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Cui, Dexuan" <decui@...rosoft.com>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "mikelley@...rosoft.com" <mikelley@...rosoft.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "bp@...en8.de" <bp@...en8.de>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH] x86/mm/cpa: Warn if set_memory_XXcrypted() fails

On Wed, 2023-10-25 at 13:03 -0500, Tom Lendacky wrote:
> 
> Reviewed-by: Tom Lendacky <thomas.lendacky@....com>

Thanks!
> > 
> 
> Under SEV, when making a page private/encrypted and the hypervisor
> does 
> not assign the page to the guest (encrypted), but says it did, then
> when 
> SEV tries to perform the PVALIDATE in the enc_status_change_finish()
> call, 
> a nested page fault (#NPF) will be generated and exit to the
> hypervisor. 
> Until the hypervisor assigns the page to the guest, the guest will
> not be 
> able to make forward progress in regards to updating or using that
> page.

Yea, mismatches between guest page tables and EPT/NPT can be trouble
for TDX as well.

> 
> And if the hypervisor returns an error when changing the page state,
> then, 
> yes, the guest will terminate.

I guess those callbacks could be changed to return an error after all
these fixes then, if you want.