linux-kernel - Re: [PATCHv2 22/29] x86/tdx: Make pages shared in ioremap()

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Date:   Mon, 7 Feb 2022 08:57:39 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Borislav Petkov <bp@...en8.de>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     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: [PATCHv2 22/29] x86/tdx: Make pages shared in ioremap()

On 2/7/22 08:27, Borislav Petkov wrote:
> On Mon, Jan 24, 2022 at 06:02:08PM +0300, Kirill A. Shutemov wrote:
>> -/*
>> - * Macros to add or remove encryption attribute
>> - */
>> -#define pgprot_encrypted(prot)	__pgprot(__sme_set(pgprot_val(prot)))
>> -#define pgprot_decrypted(prot)	__pgprot(__sme_clr(pgprot_val(prot)))
> Why can't you simply define
> 
> cc_set() and cc_clear()
> 
> helpers which either call the __sme variants or __tdx variants, the
> latter you can define the same way, respectively, as the __sme ones.

I think your basic point here is valid: Let's have a single function to
take a pgprot and turn it into an "encrypted" or "decrypted" pgprot.

But, we can't do it with functions like cc_set() and cc_clear() because
the polarity is different:

> +pgprot_t pgprot_encrypted(pgprot_t prot)
> +{
> +        if (sme_me_mask)
> +                return __pgprot(__sme_set(pgprot_val(prot)));
> +        else if (is_tdx_guest())
> +		return __pgprot(pgprot_val(prot) & ~tdx_shared_mask());
> +
> +        return prot;
> +}

For "encrypted", SME sets bits and TDX clears bits.

For "decrypted", SME clears bits and TDX sets bits.

We can surely *do* this with cc_something() helpers.  It's just not as
easy as making cc_set/cc_clear().