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

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Date:   Mon, 18 Jun 2018 17:41:06 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.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 Mon, Jun 18, 2018 at 01:59:18PM +0000, Dave Hansen wrote:
> 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?

asm/mktme.h is included from asm/page.h. It is functionally identical
other architectures.

> 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.

I do.

m68k and microblaze have different definitions of the macro depending
on CONFIG_MMU.

On arm64 it depends on CONFIG_SPARSEMEM_VMEMMAP.

> > 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.

I don't agree.

asm/mktme.h included from the single header -- asm/page.h -- and has clear
path to linux/mm.h where the default page_to_virt() is defined.

I don't see a reason to move it out of feature-specific header. The
default page_to_virt() is perfectly fine without MKTME. And it will be
obvious on grep.

-- 
 Kirill A. Shutemov