Re: [PATCHv3 16/17] x86/mm: Handle encrypted memory in page_to_virt() and __pa()

Dave Hansen
2018-06-18T13:59:23Z

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.