Re: [PATCH 2/5] efi/x86: Implement support for unaccepted memory

From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
	Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
	Sean Christopherson <seanjc@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Joerg Roedel <jroedel@suse.de>, Andi Kleen <ak@linux.intel.com>,
	Kuppuswamy Sathyanarayanan
	<sathyanarayanan.kuppuswamy@linux.intel.com>,
	David Rientjes <rientjes@google.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Ingo Molnar <mingo@redhat.com>,
	Varad Gautam <varad.gautam@suse.com>,
	Dario Faggioli <dfaggioli@suse.com>,
	x86@kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/5] efi/x86: Implement support for unaccepted memory
Date: Tue, 10 Aug 2021 22:08:36 +0300	[thread overview]
Message-ID: <20210810190836.cffj4fjqenuunwsd@black.fi.intel.com> (raw)
In-Reply-To: <07c2770e-1171-24ab-9403-91b306b5b1a4@intel.com>

On Tue, Aug 10, 2021 at 11:30:42AM -0700, Dave Hansen wrote:
> On 8/9/21 11:26 PM, Kirill A. Shutemov wrote:
> > +config UNACCEPTED_MEMORY
> > +	bool
> > +	depends on EFI_STUB
> > +	help
> > +	   Some Virtual Machine platforms, such as Intel TDX, introduce
> > +	   the concept of memory acceptance, requiring memory to be accepted
> > +	   before it can be used by the guest. This protects against a class of
> > +	   attacks by the virtual machine platform.
> > +
> > +	   This option adds support for unaccepted memory and makes such memory
> > +	   usable by kernel.
> 
> Do we really need a full-blown user-visible option here?  If we, for
> instance, just did:
> 
> config UNACCEPTED_MEMORY
> 	bool
> 	depends on EFI_STUB
> 
> it could be 'select'ed from the TDX Kconfig and no users would ever be
> bothered with it.  Would a user *ever* turn this on if they don't have
> TDX (or equivalent)?

But it's already not user selectable. Note that there's no prompt next to
the "bool". The "help" section is just for documentation. I think it can
be useful.

-- 
 Kirill A. Shutemov