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

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Date:   Tue, 4 Jan 2022 16:43:09 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
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 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.