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Subject: Re: [PATCHv3 07/17] x86/mm: Preserve KeyID on pte_modify() and
 pgprot_modify()
To:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
References: <20180612143915.68065-1-kirill.shutemov@linux.intel.com>
 <20180612143915.68065-8-kirill.shutemov@linux.intel.com>
 <8c31f6d2-6512-2726-763e-6dd1cbb0350a@intel.com>
 <20180615125720.r755xaegvfcqfr6x@black.fi.intel.com>
 <645a4ca8-ae77-dcdd-0cbc-0da467fc210d@intel.com>
 <20180615152731.3y6rre7g66rmncxr@black.fi.intel.com>
Cc:     Ingo Molnar <mingo@redhat.com>, x86@kernel.org,
        Thomas Gleixner <tglx@linutronix.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Kai Huang <kai.huang@linux.intel.com>,
        Jacob Pan <jacob.jun.pan@linux.intel.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
From:   Dave Hansen <dave.hansen@intel.com>
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Message-ID: <cbca7e78-d70b-3eae-1c73-6ad859661b8a@intel.com>
Date:   Fri, 15 Jun 2018 08:31:57 -0700
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On 06/15/2018 08:27 AM, Kirill A. Shutemov wrote:
> On Fri, Jun 15, 2018 at 01:43:03PM +0000, Dave Hansen wrote:
>> On 06/15/2018 05:57 AM, Kirill A. Shutemov wrote:
>>>>> +#define _PAGE_CHG_MASK	(PTE_PFN_MASK_MAX | _PAGE_PCD | _PAGE_PWT |		\
>>>>>  			 _PAGE_SPECIAL | _PAGE_ACCESSED | _PAGE_DIRTY |	\
>>>>>  			 _PAGE_SOFT_DIRTY)
>>>>>  #define _HPAGE_CHG_MASK (_PAGE_CHG_MASK | _PAGE_PSE)
>>>> This makes me a bit nervous.  We have some places (here) where we
>>>> pretend that the KeyID is part of the paddr and then other places like
>>>> pte_pfn() where it's not.
>>> Other option is to include KeyID mask into _PAGE_CHG_MASK. But it means
>>> _PAGE_CHG_MASK would need to reference *two* variables: physical_mask and
>>> mktme_keyid_mask. I mentioned this in the commit message.
>>
>> Why can't it be one variable with a different name that's populated by
>> OR'ing physical_mask and mktme_keyid_mask together?
> 
> My point is that we don't need variables at all here.
> 
> Architecture defines range of bits in PTE used for PFN. MKTME reduces the
> number of bits for PFN. PTE_PFN_MASK_MAX represents the original
> architectural range, before MKTME stole these bits.
> 
> PTE_PFN_MASK_MAX is constant -- on x86-64 bits 51:12 -- regardless of
> MKTME support.

Then please just rename the make PTE_<SOMETHING>_MASK where <SOMETHING>
includes both the concept of a physical address and a MKTME keyID.  Just
don't call it a pfn if it is not used in physical addressing.

>> Whatever you come up with will probably fine, as long as things that are
>> called "PFN" or physical address don't also get used for keyID bits.
> 
> We are arguing about macros used exactly once. Is it really so confusing?

Yes.