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

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Date:   Mon, 3 Jan 2022 08:50:12 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Borislav Petkov <bp@...en8.de>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.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 1/3/22 7:15 AM, Kirill A. Shutemov wrote:
> On Mon, Jan 03, 2022 at 03:29:44PM +0100, Borislav Petkov wrote:
>> On Mon, Jan 03, 2022 at 05:17:05PM +0300, Kirill A. Shutemov wrote:
>>> I'm not sure how to unwind this dependency hell. Any clues?
>> Forward-declaration maybe?
>>
>> I.e., something like
>>
>> struct task_struct;
>>
>> at the top of arch/x86/include/asm/switch_to.h, for example...
> Forward-declaration only works if you refer the struct/union by pointer,
> not value.
> 
> And pgprot_t is not always a struct and when it is a struct it is
> anonymous.
> 
> See "git grep 'typedef.*pgprot_t;'".

In the end, the new functions get used like this:

	prot = pgprot_decrypted(prot);

I think they _could_ be:

	pgprot_set_decrypted(&prot);

Which would let you have a declaration like this:

	extern void pgprot_cc_set_decrypted(pgprot_t *prot);

It does not exactly give me warm and fuzzy feelings, but it would work
around the header problem.