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SubjectRe: [PATCH 19/26] x86/tdx: Make pages shared in ioremap()
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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);
>

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