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

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Message-ID: <20220104191424.oly2gqm4ltzj5wo3@box.shutemov.name>
Date:   Tue, 4 Jan 2022 22:14:24 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        "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 Mon, Jan 03, 2022 at 09:10:59PM +0300, Kirill A. Shutemov wrote:
> On Mon, Jan 03, 2022 at 08:50:12AM -0800, Dave Hansen wrote:
> > 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.
> 
> Apart for being ugly, I don't see how it solves anything. How would you
> forward-declare a typedef?

I see two possible options (I hate both): leave it defined in per-arch
<asm/pgtable.h> or move it to <linux/mm.h> next to user in
io_remap_pfn_range().

-- 
 Kirill A. Shutemov