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

[Kirill A. Shutemov]

On Tue, Jun 12, 2018 at 02:58:38PM +0000, Mika Penttilä wrote:
> 
> 
> 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@xxxxxxxxxxxxxxx>
> > ---
> >  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?

1/2 of kernel address space or 1/4 of whole address space.

> 
> > +	 */
> > +	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);

Ouch. Thanks for noticing this.

> >  
> >  	/* 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)) {

Yeah... :/

Here's fixup.

diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index 3d8ef8cb97e1..ef437c8d5f34 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -103,8 +103,8 @@ void __init kernel_randomize_memory(void)
 		return;
 
 	/*
-	 * Upper limit for direct mapping size is 1/4 of whole virtual
-	 * address space
+	 * Upper limit for direct mapping size is half of kernel address
+	 * space.
 	 */
 	kaslr_regions[0].size_tb = 1 << (__VIRTUAL_MASK_SHIFT - 1 - TB_SHIFT);
 	kaslr_regions[1].size_tb = VMALLOC_SIZE_TB;
@@ -117,7 +117,7 @@ void __init kernel_randomize_memory(void)
 
 	setup_direct_mapping_size();
 
-	memory_tb = direct_mapping_size * mktme_nr_keyids + 1;
+	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 3e5322bf035e..70f6eff093d8 100644
--- a/arch/x86/mm/mktme.c
+++ b/arch/x86/mm/mktme.c
@@ -110,7 +110,7 @@ void __init setup_direct_mapping_size(void)
 	 *
 	 * Disable MKTME instead.
 	 */
-	if (direct_mapping_size > available_va / mktme_nr_keyids + 1) {
+	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();
-- 
 Kirill A. Shutemov