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

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Message-ID: <3fd5d9b4-87ac-4f3e-bb89-60813808389b@amd.com>
Date:   Wed, 5 Jan 2022 08:16:49 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Dave Hansen <dave.hansen@...el.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     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 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.

Thanks,
Tom


>