Re: [PATCHv3 14/17] x86/mm: Introduce direct_mapping_size

["Mika Penttilä" <mika.penttila@nextfour.com>]

On 12.06.2018 17:39, Kirill A. Shutemov wrote:
> Kernel need to have a way to access encrypted memory. We are going to
> use per-KeyID direct mapping to facilitate the access with minimal
> overhead.
>
> Direct mapping for each KeyID will be put next to each other in the
> virtual address space. We need to have a way to find boundaries of
> direct mapping for particular KeyID.
>
> The new variable direct_mapping_size specifies the size of direct
> mapping. With the value, it's trivial to find direct mapping for
> KeyID-N: PAGE_OFFSET + N * direct_mapping_size.
>
> Size of direct mapping is calculated during KASLR setup. If KALSR is
> disable it happens during MKTME initialization.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
>  arch/x86/include/asm/mktme.h   |  2 ++
>  arch/x86/include/asm/page_64.h |  1 +
>  arch/x86/kernel/head64.c       |  2 ++
>  arch/x86/mm/kaslr.c            | 21 ++++++++++++---
>  arch/x86/mm/mktme.c            | 48 ++++++++++++++++++++++++++++++++++
>  5 files changed, 71 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/include/asm/mktme.h b/arch/x86/include/asm/mktme.h
> index 9363b989a021..3bf481fe3f56 100644
> --- a/arch/x86/include/asm/mktme.h
> +++ b/arch/x86/include/asm/mktme.h
> @@ -40,6 +40,8 @@ int page_keyid(const struct page *page);
>  
>  void mktme_disable(void);
>  
> +void setup_direct_mapping_size(void);
> +
>  #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 939b1cff4a7b..53c32af895ab 100644
> --- a/arch/x86/include/asm/page_64.h
> +++ b/arch/x86/include/asm/page_64.h
> @@ -14,6 +14,7 @@ extern unsigned long phys_base;
>  extern unsigned long page_offset_base;
>  extern unsigned long vmalloc_base;
>  extern unsigned long vmemmap_base;
> +extern unsigned long direct_mapping_size;
>  
>  static inline unsigned long __phys_addr_nodebug(unsigned long x)
>  {
> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> index a21d6ace648e..b6175376b2e1 100644
> --- a/arch/x86/kernel/head64.c
> +++ b/arch/x86/kernel/head64.c
> @@ -59,6 +59,8 @@ EXPORT_SYMBOL(vmalloc_base);
>  unsigned long vmemmap_base __ro_after_init = __VMEMMAP_BASE_L4;
>  EXPORT_SYMBOL(vmemmap_base);
>  #endif
> +unsigned long direct_mapping_size __ro_after_init = -1UL;
> +EXPORT_SYMBOL(direct_mapping_size);
>  
>  #define __head	__section(.head.text)
>  
> diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
> index 4408cd9a3bef..3d8ef8cb97e1 100644
> --- a/arch/x86/mm/kaslr.c
> +++ b/arch/x86/mm/kaslr.c
> @@ -69,6 +69,15 @@ static inline bool kaslr_memory_enabled(void)
>  	return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN);
>  }
>  
> +#ifndef CONFIG_X86_INTEL_MKTME
> +static void __init setup_direct_mapping_size(void)
> +{
> +	direct_mapping_size = max_pfn << PAGE_SHIFT;
> +	direct_mapping_size = round_up(direct_mapping_size, 1UL << TB_SHIFT);
> +	direct_mapping_size += (1UL << TB_SHIFT) * CONFIG_MEMORY_PHYSICAL_PADDING;
> +}
> +#endif
> +
>  /* Initialize base and padding for each memory region randomized with KASLR */
>  void __init kernel_randomize_memory(void)
>  {
> @@ -93,7 +102,11 @@ void __init kernel_randomize_memory(void)
>  	if (!kaslr_memory_enabled())
>  		return;
>  
> -	kaslr_regions[0].size_tb = 1 << (__PHYSICAL_MASK_SHIFT - TB_SHIFT);
> +	/*
> +	 * Upper limit for direct mapping size is 1/4 of whole virtual
> +	 * address space

or 1/2?

> +	 */
> +	kaslr_regions[0].size_tb = 1 << (__VIRTUAL_MASK_SHIFT - 1 - TB_SHIFT);



>  	kaslr_regions[1].size_tb = VMALLOC_SIZE_TB;
>  
>  	/*
> @@ -101,8 +114,10 @@ void __init kernel_randomize_memory(void)
>  	 * add padding if needed (especially for memory hotplug support).
>  	 */
>  	BUG_ON(kaslr_regions[0].base != &page_offset_base);
> -	memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
> -		CONFIG_MEMORY_PHYSICAL_PADDING;
> +
> +	setup_direct_mapping_size();
> +
> +	memory_tb = direct_mapping_size * mktme_nr_keyids + 1;

parenthesis ?

memory_tb = direct_mapping_size * (mktme_nr_keyids + 1);


>  
>  	/* Adapt phyiscal memory region size based on available memory */
>  	if (memory_tb < kaslr_regions[0].size_tb)
> diff --git a/arch/x86/mm/mktme.c b/arch/x86/mm/mktme.c
> index 43a44f0f2a2d..3e5322bf035e 100644
> --- a/arch/x86/mm/mktme.c
> +++ b/arch/x86/mm/mktme.c
> @@ -89,3 +89,51 @@ static bool need_page_mktme(void)
>  struct page_ext_operations page_mktme_ops = {
>  	.need = need_page_mktme,
>  };
> +
> +void __init setup_direct_mapping_size(void)
> +{
> +	unsigned long available_va;
> +
> +	/* 1/4 of virtual address space is didicated for direct mapping */
> +	available_va = 1UL << (__VIRTUAL_MASK_SHIFT - 1);
> +
> +	/* How much memory the systrem has? */
> +	direct_mapping_size = max_pfn << PAGE_SHIFT;
> +	direct_mapping_size = round_up(direct_mapping_size, 1UL << 40);
> +
> +	if (mktme_status != MKTME_ENUMERATED)
> +		goto out;
> +
> +	/*
> +	 * Not enough virtual address space to address all physical memory with
> +	 * MKTME enabled. Even without padding.
> +	 *
> +	 * Disable MKTME instead.
> +	 */
> +	if (direct_mapping_size > available_va / mktme_nr_keyids + 1) {

parenthesis again?

if (direct_mapping_size > available_va / (mktme_nr_keyids + 1)) {



> +		pr_err("x86/mktme: Disabled. Not enough virtual address space\n");
> +		pr_err("x86/mktme: Consider switching to 5-level paging\n");
> +		mktme_disable();
> +		goto out;
> +	}
> +
> +	/*
> +	 * Virtual address space is divided between per-KeyID direct mappings.
> +	 */
> +	available_va /= mktme_nr_keyids + 1
> +out:
> +	/* Add padding, if there's enough virtual address space */
> +	direct_mapping_size += (1UL << 40) * CONFIG_MEMORY_PHYSICAL_PADDING;
> +	if (direct_mapping_size > available_va)
> +		direct_mapping_size = available_va;
> +}
> +
> +static int __init mktme_init(void)
> +{
> +	/* KASLR didn't initialized it for us. */
> +	if (direct_mapping_size == -1UL)
> +		setup_direct_mapping_size();
> +
> +	return 0;
> +}
> +arch_initcall(mktme_init)