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Subject: Re: [PATCHv4 17/18] x86/mm: Handle encrypted memory in page_to_virt()
 and __pa()
References: <20180626142245.82850-1-kirill.shutemov@linux.intel.com>
 <20180626142245.82850-18-kirill.shutemov@linux.intel.com>
From: Dave Hansen <dave.hansen@intel.com>
Message-ID: <1609f2b4-4638-8b9d-4dc7-fcb3303739cd@intel.com>
Date: Tue, 26 Jun 2018 09:38:23 -0700
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Sender: owner-linux-mm@kvack.org
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To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, 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>
Cc: Kai Huang <kai.huang@linux.intel.com>, Jacob Pan <jacob.jun.pan@linux.intel.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org

> diff --git a/arch/x86/include/asm/mktme.h b/arch/x86/include/asm/mktme.h
> index ba83fba4f9b3..dbfbd955da98 100644
> --- a/arch/x86/include/asm/mktme.h
> +++ b/arch/x86/include/asm/mktme.h
> @@ -29,6 +29,9 @@ void arch_free_page(struct page *page, int order);
>  
>  int sync_direct_mapping(void);
>  
> +#define page_to_virt(x) \
> +	(__va(PFN_PHYS(page_to_pfn(x))) + page_keyid(x) * direct_mapping_size)

Please put this in a generic header so that this hunk represents the
*default* x86 implementation that is used universally on x86.  Then,
please do

#ifndef CONFIG_MKTME_WHATEVER
#define page_keyid(x) (0)
#endif

>  #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;

There are almost *surely* performance implications from this that affect
anyone with this compile option turned on.  There's now a 64-bit integer
division operation which is used in places like kfree().

That's a show-stopper for me until we've done some pretty comprehensive
performance analysis of this, which means much more than one kernel
compile test on one system.