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

Kirill A. Shutemov
2018-06-18T13:35:00Z

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>.

> > #else
> > #define mktme_keyid_mask ((phys_addr_t)0)
> > #define mktme_nr_keyids 0
> > diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
> > index 53c32af895ab..ffad496aadad 100644
> > --- a/arch/x86/include/asm/page_64.h
> > +++ b/arch/x86/include/asm/page_64.h
> > @@ -23,7 +23,7 @@ static inline unsigned long __phys_addr_nodebug(unsigned long x)
> > /* use the carry flag to determine if x was < __START_KERNEL_map */
> > x = y + ((x > y) ? phys_base : (__START_KERNEL_map - PAGE_OFFSET));
> >
> > - return x;
> > + return x % direct_mapping_size;
> > }
>
> What are the performance implications of this patch?

Let me collect the numbers.

--
Kirill A. Shutemov