Re: [PATCH v10 21/45] x86/mm: Add support to validate memory when changing C-bit

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, linux-coco@lists.linux.dev,
	linux-mm@kvack.org, 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>,
	Michael Roth <michael.roth@amd.com>,
	Vlastimil Babka <vbabka@suse.cz>, Andi Kleen <ak@linux.intel.com>,
	"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
	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
Date: Tue, 15 Feb 2022 16:15:22 +0300	[thread overview]
Message-ID: <20220215131522.l3xytgmy4ufrgnlb@box.shutemov.name> (raw)
In-Reply-To: <YguimA5Au4t2A4oj@zn.tnic>

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