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

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Date:   Wed, 5 Jan 2022 19:02:26 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.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 Wed, Jan 05, 2022 at 08:16:49AM -0600, Tom Lendacky wrote:
> On 1/4/22 6:43 PM, Dave Hansen wrote:
> > On 1/4/22 4:31 PM, Kirill A. Shutemov wrote:
> > > On Tue, Jan 04, 2022 at 12:36:06PM -0800, Dave Hansen wrote:
> > > > @@ -57,7 +58,6 @@ typedef struct { unsigned long iopte; }
> > > >   typedef struct { unsigned long pmd; } pmd_t;
> > > >   typedef struct { unsigned long pgd; } pgd_t;
> > > >   typedef struct { unsigned long ctxd; } ctxd_t;
> > > > -typedef struct { unsigned long pgprot; } pgprot_t;
> > > >   typedef struct { unsigned long iopgprot; } iopgprot_t;
> > > >   #define pte_val(x)	((x).pte)
> > > > @@ -85,7 +85,6 @@ typedef unsigned long iopte_t;
> > > >   typedef unsigned long pmd_t;
> > > >   typedef unsigned long pgd_t;
> > > >   typedef unsigned long ctxd_t;
> > > > -typedef unsigned long pgprot_t;
> > > >   typedef unsigned long iopgprot_t;
> > > >   #define pte_val(x)	(x)
> > > 
> > > Any arch that use STRICT_MM_TYPECHECKS hacks will get broken if compiled
> > > without the define (as sparc by default).
> > 
> > My read of STRICT_MM_TYPECHECKS was that "typedef unsigned long
> > pgprot_t" produces better code, but "typedef struct { unsigned long
> > pgprot; } pgprot_t;" produces better type checking.
> > 
> > I just compiled these patches on sparc with no issues.
> > 
> > ...
> > > Is it the way to go we want?
> > 
> > I _think_ this was all a result of some review feedback from Tom
> > Lendacky about where the encryption-modifying pgprot helpers got placed
> > in the code.  I don't feel strongly about it, but I'm not quite sure
> > that this is worth the trouble.
> > 
> > I'd be curious what Tom thinks now that he's gotten a peek at what it's
> > going to take to address his concerns.
> 
> I have vague memories of pgprot_t and what a pain it could be, which is why
> my feedback suggested putting it in cc_platform.c, but said there might be
> issues :)
> 
> I'm fine with it living somewhere else, just thought it would be nice to
> have everything consolidated, if possible.

In this case I would rather leave it in <asm/pgtable.h>. We still can
rename it to cc_pgprot_decrypted()/cc_pgprot_encrypted().

-- 
 Kirill A. Shutemov