Subject: Re: [PATCH 19/26] x86/tdx: Make pages shared in ioremap()
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
Cc:     Borislav Petkov <bp@alien8.de>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>, tglx@linutronix.de,
        mingo@redhat.com, luto@kernel.org, peterz@infradead.org,
        sathyanarayanan.kuppuswamy@linux.intel.com, aarcange@redhat.com,
        ak@linux.intel.com, dan.j.williams@intel.com, david@redhat.com,
        hpa@zytor.com, jgross@suse.com, jmattson@google.com,
        joro@8bytes.org, jpoimboe@redhat.com, knsathya@kernel.org,
        pbonzini@redhat.com, sdeep@vmware.com, seanjc@google.com,
        tony.luck@intel.com, vkuznets@redhat.com, wanpengli@tencent.com,
        x86@kernel.org, linux-kernel@vger.kernel.org
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From:   Dave Hansen <dave.hansen@intel.com>
Message-ID: <50dfa0db-fcd1-3c54-d982-237d2c9df431@intel.com>
Date:   Tue, 4 Jan 2022 16:43:09 -0800
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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.