linux-kernel - Re: [PATCHv3 16/17] x86/mm: Handle encrypted memory in page_to_virt() and _

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Message-ID: <48fe7072-e92d-959a-67f7-ded82124f79f@intel.com>
Date:   Mon, 18 Jun 2018 06:59:18 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Kai Huang <kai.huang@...ux.intel.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv3 16/17] x86/mm: Handle encrypted memory in page_to_virt()
 and __pa()

On 06/18/2018 06:34 AM, Kirill A. Shutemov wrote:
> On Wed, Jun 13, 2018 at 06:43:08PM +0000, Dave Hansen wrote:
>>> diff --git a/arch/x86/include/asm/mktme.h b/arch/x86/include/asm/mktme.h
>>> index efc0d4bb3b35..d6edcabacfc7 100644
>>> --- a/arch/x86/include/asm/mktme.h
>>> +++ b/arch/x86/include/asm/mktme.h
>>> @@ -43,6 +43,9 @@ void mktme_disable(void);
>>>  void setup_direct_mapping_size(void);
>>>  int sync_direct_mapping(void);
>>>  
>>> +#define page_to_virt(x) \
>>> +	(__va(PFN_PHYS(page_to_pfn(x))) + page_keyid(x) * direct_mapping_size)
>>
>> This looks like a super important memory management function being
>> defined in some obscure Intel-specific feature header.  How does that work?
> 
> No magic. It overwrites define in <linux/mm.h>.

It frankly looks like magic to me.  How can this possibly work without
ensuring that asm/mktme.h is #included everywhere on every file compiled
for the entire architecture?

If we look at every definition of page_to_virt() on every architecture
in the kernel, we see it uniquely defined in headers that look rather
generic.  I don't see any precedent for feature-specific definitions.

> arch/arm64/include/asm/memory.h:#define page_to_virt(page)	((void *)((__page_to_voff(page)) | PAGE_OFFSET))
> arch/hexagon/include/asm/page.h:#define page_to_virt(page)	__va(page_to_phys(page))
> arch/m68k/include/asm/page_mm.h:#define page_to_virt(page) ({						\
> arch/m68k/include/asm/page_no.h:#define page_to_virt(page)	__va(((((page) - mem_map) << PAGE_SHIFT) + PAGE_OFFSET))
> arch/microblaze/include/asm/page.h:#  define page_to_virt(page)   __va(page_to_pfn(page) << PAGE_SHIFT)
> arch/microblaze/include/asm/page.h:#  define page_to_virt(page)	(pfn_to_virt(page_to_pfn(page)))
> arch/nios2/include/asm/page.h:#define page_to_virt(page)	\
> arch/riscv/include/asm/page.h:#define page_to_virt(page)	(pfn_to_virt(page_to_pfn(page)))
> arch/s390/include/asm/page.h:#define page_to_virt(page)	pfn_to_virt(page_to_pfn(page))
> arch/xtensa/include/asm/page.h:#define page_to_virt(page)	__va(page_to_pfn(page) << PAGE_SHIFT)

*If* you do this, I think it 100% *HAS* to be done in a central header,
like x86's page.h.  We need a single x86 macro for this, not something
which can and will change based on #include ordering and Kconfig.