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

Mika Penttilä
2018-06-12T14:58:49Z

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)