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

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Message-ID: <33914dc1-37e8-f0bb-6468-71c3b5f4169d@amd.com>
Date:   Mon, 27 Dec 2021 09:07:10 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        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: [PATCH 19/26] x86/tdx: Make pages shared in ioremap()

On 12/24/21 5:03 AM, Kirill A. Shutemov wrote:
> 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);

Why can't this follow the cc_platform_has() logic and maybe even live in
the cc_platform.c file (though there might be issues with that, I haven't
really looked)?

	if (sme_me_mask)
		return __pgprot(__sme_set(pgprot_val(prot)));
	else if (is_tdx_guest())
		return return __pgprot(pgprot_val(prot) & ~tdx_shared_mask());

	return prot;

and maybe even it call it cc_pgrot_encrypted()?

Just a thought.

Thanks,
Tom

> 
> 	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);
>