linux-kernel - Re: [PATCH 19/26] x86/tdx: Make pages shared in ioremap()

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Date:   Tue, 28 Dec 2021 19:39:46 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Dave Hansen <dave.hansen@...el.com>,
        Tom Lendacky <thomas.lendacky@....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: [PATCH 19/26] x86/tdx: Make pages shared in ioremap()

On Mon, Dec 27, 2021 at 05:14:36PM +0300, Kirill A. Shutemov wrote:
> On Mon, Dec 27, 2021 at 12:51:21PM +0100, Borislav Petkov wrote:
> > On Fri, Dec 24, 2021 at 02:03:00PM +0300, Kirill A. Shutemov wrote:
> > > Okay. Meanwhile I leave it this way:
> > > 
> > > 	pgprot_t pgprot_cc_encrypted(pgprot_t prot)
> > > 	{
> > > 		if (cc_platform_has(CC_ATTR_MEM_ENCRYPT)) {
> > > 			if (cc_platform_has(CC_ATTR_GUEST_TDX))
> > > 				return __pgprot(pgprot_val(prot) & ~tdx_shared_mask());
> > > 			else if (sme_me_mask)
> > > 				return __pgprot(__sme_set(pgprot_val(prot)));
> > > 			else
> > > 				WARN_ON_ONCE(1);
> > 
> > I'm wondering if defining a generic cc_attr especially for this:
> > 
> > 	if (cc_platform_has(CC_ATTR_MEMORY_SHARING))
> > 
> > to mean, the CC guest needs to do special stuff in order to share memory
> > with the host (naming sucks, ofc) would be cleaner?
> 
> Looks like CC_ATTR_MEM_ENCRYPT already does this. The attribute doesn't
> have much meaning beyond that, no?

It means that *some* memory encryption - guest or host - is in use.

But my point about removing the outer check is bull - you need the
TDX/SEV checks too to figure out which mask to use.

So, reading Tom's latest email, having

	cc_pgprot_encrypted(prot)

and
	cc_pgprot_decrypted(prot)

in cc_platform.c and which hide all that logic inside doesn't sound like
a bad idea. And cc_platform.c already looks at sme_me_mask and we do
that there for the early path so I guess that's probably halfway fine...

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette