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Date:   Tue, 15 Feb 2022 16:15:22 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     Borislav Petkov <bp@alien8.de>
Cc:     Brijesh Singh <brijesh.singh@amd.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org,
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        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ard Biesheuvel <ardb@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Jim Mattson <jmattson@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Sergio Lopez <slp@redhat.com>, Peter Gonda <pgonda@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Dov Murik <dovmurik@linux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@ibm.com>,
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        Vlastimil Babka <vbabka@suse.cz>,
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        brijesh.ksingh@gmail.com, tony.luck@intel.com, marcorr@google.com,
        sathyanarayanan.kuppuswamy@linux.intel.com
Subject: Re: [PATCH v10 21/45] x86/mm: Add support to validate memory when
 changing C-bit
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On Tue, Feb 15, 2022 at 01:54:48PM +0100, Borislav Petkov wrote:
> On Tue, Feb 15, 2022 at 03:43:31PM +0300, Kirill A. Shutemov wrote:
> > I don't think it works. TDX and SME/SEV has opposite polarity of the mask.
> > SME/SEV has to clear the mask to share the page. TDX has to set it.
> > 
> > Making a single global mask only increases confusion.
> 
> Didn't you read the rest of the thread with Tom's suggestion? I think
> there's a merit in having a cc_vendor or so which explicitly states what
> type of HV the kernel runs on...

I have no problem with cc_vendor idea. It looks good.

Regarding the masks, if we want to have common ground here we can add two
mask: cc_enc_mask and cc_dec_mask. And then

pgprotval_t cc_enc(pgprotval_t protval)
{
	protval |= cc_enc_mask;
	protval &= ~cc_dec_mask;
	return protval;
}

pgprotval_t cc_dec(pgprotval_t protval)
{
	protval |= cc_dec_mask;
	protval &= ~cc_enc_mask;
	return protval;
}

It assumes (cc_enc_mask & cc_dec_mask) == 0.

Any opinions?

-- 
 Kirill A. Shutemov