linux-kernel - Re: [PATCHv3 02/32] x86/coco: Add API to handle encryption mask

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Message-ID: <20220222135253.k6ayc7zgpqrsoiex@black.fi.intel.com>
Date:   Tue, 22 Feb 2022 16:52:53 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Dave Hansen <dave.hansen@...el.com>, tglx@...utronix.de,
        mingo@...hat.com, luto@...nel.org, peterz@...radead.org,
        sathyanarayanan.kuppuswamy@...ux.intel.com, aarcange@...hat.com,
        ak@...ux.intel.com, dan.j.williams@...el.com, david@...hat.com,
        hpa@...or.com, jgross@...e.com, jmattson@...gle.com,
        joro@...tes.org, jpoimboe@...hat.com, knsathya@...nel.org,
        pbonzini@...hat.com, sdeep@...are.com, seanjc@...gle.com,
        tony.luck@...el.com, vkuznets@...hat.com, wanpengli@...cent.com,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 02/32] x86/coco: Add API to handle encryption mask

On Tue, Feb 22, 2022 at 02:37:27PM +0100, Borislav Petkov wrote:
> On Tue, Feb 22, 2022 at 02:03:12PM +0300, Kirill A. Shutemov wrote:
> > I would rather make cc_mkenc()/cc_mkdec() to operate on u64 (or
> > phys_addr_t?) while pgprot_encrypted()/pgprot_decrypted() cover pgprot_t.
> > It also makes set_memory cleaner:
> > 
> > 	cpa.mask_set = __pgprot(enc ? cc_mkenc(0) : cc_mkdec(0));
> > 	cpa.mask_clr = __pgprot(enc ? cc_mkdec(0) : cc_mkenc(0));
> > 
> > Opinions?
> 
> Right, do I see it correctly that the cc_mk{enc,dec}() things should
> take a u64 as an argument and return a pgprot_t, and that would be the
> most optimal way for all the use cases?

No, not really. With u64-in-u64-out in tdx_enc_status_changed() we have 

	if (!enc) {
		start |= cc_mkdec(0);
		end |= cc_mkdec(0);
	}

to iterate over the range of physical addresses with shared bit set.
With u64-in-pgprot_t-out we will have do add pgprot_val() there.

We will have more cases like this in attestation code when we need to do
hypercall on a shared page.

-- 
 Kirill A. Shutemov