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

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Date:   Fri, 24 Dec 2021 14:03:00 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
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 Thu, Dec 23, 2021 at 10:09:26PM +0100, Borislav Petkov wrote:
> On Thu, Dec 23, 2021 at 11:56:04PM +0300, Kirill A. Shutemov wrote:
> > Except CC_ATTR_MEM_ENCRYPT is true for TDX too, so it will also depend on
> > check order. It is fragile.
> 
> So the query you wanna do is:
> 
> 	if (memory encryption in use)
> 		use mask;
> 
> and the mask you use depends on whether it is SEV or TDX. Right?
> 
> If so, you can either do a cc_get_mask() function which gives you either
> the SEV or TDX mask or simply do:
> 
> 	if (CC_ATTR_MEM_ENCRYPT) {
> 		if (CC_ATTR_GUEST_TDX)
> 			mask = tdx_shared_mask();
> 		else if (sme_me_mask)
> 			mask = sme_me_mask;
> 	}
> 
> Yeah, sme_me_mask has become synonymous with the kernel running as a AMD
> confidential guest. I need to think about how to make this cleaner...

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);
		}

		return prot;
	}
	EXPORT_SYMBOL_GPL(pgprot_cc_encrypted);

	pgprot_t pgprot_cc_decrypted(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_clr(pgprot_val(prot)));
			else
				WARN_ON_ONCE(1);
		}

		return prot;
	}
	EXPORT_SYMBOL_GPL(pgprot_cc_decrypted);

-- 
 Kirill A. Shutemov