Commit b27a43c1 authored by Suresh Siddha's avatar Suresh Siddha Committed by Ingo Molnar
Browse files

x86, cpa: make the kernel physical mapping initialization a two pass sequence, fix 



Jeremy Fitzhardinge wrote:

> I'd noticed that current tip/master hasn't been booting under Xen, and I
> just got around to bisecting it down to this change.
>
> commit 065ae73c5462d42e9761afb76f2b52965ff45bd6
> Author: Suresh Siddha <suresh.b.siddha@intel.com>
>
>    x86, cpa: make the kernel physical mapping initialization a two pass sequence
>
> This patch is causing Xen to fail various pagetable updates because it
> ends up remapping pagetables to RW, which Xen explicitly prohibits (as
> that would allow guests to make arbitrary changes to pagetables, rather
> than have them mediated by the hypervisor).

Instead of making init a two pass sequence, to satisfy the Intel's TLB
Application note (developer.intel.com/design/processor/applnots/317080.pdf
Section 6 page 26), we preserve the original page permissions
when fragmenting the large mappings and don't touch the existing memory
mapping (which satisfies Xen's requirements).

Only open issue is: on a native linux kernel, we will go back to mapping
the first 0-1GB kernel identity mapping as executable (because of the
static mapping setup in head_64.S). We can fix this in a different
patch if needed.

Signed-off-by: default avatarSuresh Siddha <suresh.b.siddha@intel.com>
Acked-by: default avatarJeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent ad2cde16

arch/x86/mm/init_64.c

+61 −88
Original line number Diff line number Diff line
@@ -270,10 +270,9 @@ static __ref void unmap_low_page(void *adr) 
	early_iounmap(adr, PAGE_SIZE);

}



static int physical_mapping_iter;



static unsigned long __meminit

phys_pte_init(pte_t *pte_page, unsigned long addr, unsigned long end)

phys_pte_init(pte_t *pte_page, unsigned long addr, unsigned long end,

	      pgprot_t prot)

{

	unsigned pages = 0;

	unsigned long last_map_addr = end;
@@ -291,35 +290,40 @@ phys_pte_init(pte_t *pte_page, unsigned long addr, unsigned long end) 
			break;

		}



		/*

		 * We will re-use the existing mapping.

		 * Xen for example has some special requirements, like mapping

		 * pagetable pages as RO. So assume someone who pre-setup

		 * these mappings are more intelligent.

		 */

		if (pte_val(*pte))

			goto repeat_set_pte;

			continue;



		if (0)

			printk("   pte=%p addr=%lx pte=%016lx\n",

			       pte, addr, pfn_pte(addr >> PAGE_SHIFT, PAGE_KERNEL).pte);

		pages++;

repeat_set_pte:

		set_pte(pte, pfn_pte(addr >> PAGE_SHIFT, PAGE_KERNEL));

		set_pte(pte, pfn_pte(addr >> PAGE_SHIFT, prot));

		last_map_addr = (addr & PAGE_MASK) + PAGE_SIZE;

	}



	if (physical_mapping_iter == 1)

	update_page_count(PG_LEVEL_4K, pages);



	return last_map_addr;

}



static unsigned long __meminit

phys_pte_update(pmd_t *pmd, unsigned long address, unsigned long end)

phys_pte_update(pmd_t *pmd, unsigned long address, unsigned long end,

		pgprot_t prot)

{

	pte_t *pte = (pte_t *)pmd_page_vaddr(*pmd);



	return phys_pte_init(pte, address, end);

	return phys_pte_init(pte, address, end, prot);

}



static unsigned long __meminit

phys_pmd_init(pmd_t *pmd_page, unsigned long address, unsigned long end,

			 unsigned long page_size_mask)

	      unsigned long page_size_mask, pgprot_t prot)

{

	unsigned long pages = 0;

	unsigned long last_map_addr = end;
@@ -330,6 +334,7 @@ phys_pmd_init(pmd_t *pmd_page, unsigned long address, unsigned long end, 
		unsigned long pte_phys;

		pmd_t *pmd = pmd_page + pmd_index(address);

		pte_t *pte;

		pgprot_t new_prot = prot;



		if (address >= end) {

			if (!after_bootmem) {
@@ -343,45 +348,58 @@ phys_pmd_init(pmd_t *pmd_page, unsigned long address, unsigned long end, 
			if (!pmd_large(*pmd)) {

				spin_lock(&init_mm.page_table_lock);

				last_map_addr = phys_pte_update(pmd, address,

								end);

								end, prot);

				spin_unlock(&init_mm.page_table_lock);

				continue;

			}

			goto repeat_set_pte;

			/*

			 * If we are ok with PG_LEVEL_2M mapping, then we will

			 * use the existing mapping,

			 *

			 * Otherwise, we will split the large page mapping but

			 * use the same existing protection bits except for

			 * large page, so that we don't violate Intel's TLB

			 * Application note (317080) which says, while changing

			 * the page sizes, new and old translations should

			 * not differ with respect to page frame and

			 * attributes.

			 */

			if (page_size_mask & (1 << PG_LEVEL_2M))

				continue;

			new_prot = pte_pgprot(pte_clrhuge(*(pte_t *)pmd));

		}



		if (page_size_mask & (1<<PG_LEVEL_2M)) {

			pages++;

repeat_set_pte:

			spin_lock(&init_mm.page_table_lock);

			set_pte((pte_t *)pmd,

				pfn_pte(address >> PAGE_SHIFT, PAGE_KERNEL_LARGE));

				pfn_pte(address >> PAGE_SHIFT,

					__pgprot(pgprot_val(prot) | _PAGE_PSE)));

			spin_unlock(&init_mm.page_table_lock);

			last_map_addr = (address & PMD_MASK) + PMD_SIZE;

			continue;

		}



		pte = alloc_low_page(&pte_phys);

		last_map_addr = phys_pte_init(pte, address, end);

		last_map_addr = phys_pte_init(pte, address, end, new_prot);

		unmap_low_page(pte);



		spin_lock(&init_mm.page_table_lock);

		pmd_populate_kernel(&init_mm, pmd, __va(pte_phys));

		spin_unlock(&init_mm.page_table_lock);

	}

	if (physical_mapping_iter == 1)

	update_page_count(PG_LEVEL_2M, pages);

	return last_map_addr;

}



static unsigned long __meminit

phys_pmd_update(pud_t *pud, unsigned long address, unsigned long end,

			 unsigned long page_size_mask)

		unsigned long page_size_mask, pgprot_t prot)

{

	pmd_t *pmd = pmd_offset(pud, 0);

	unsigned long last_map_addr;



	last_map_addr = phys_pmd_init(pmd, address, end, page_size_mask);

	last_map_addr = phys_pmd_init(pmd, address, end, page_size_mask, prot);

	__flush_tlb_all();

	return last_map_addr;

}
@@ -398,6 +416,7 @@ phys_pud_init(pud_t *pud_page, unsigned long addr, unsigned long end, 
		unsigned long pmd_phys;

		pud_t *pud = pud_page + pud_index(addr);

		pmd_t *pmd;

		pgprot_t prot = PAGE_KERNEL;



		if (addr >= end)

			break;
@@ -411,16 +430,28 @@ phys_pud_init(pud_t *pud_page, unsigned long addr, unsigned long end, 
		if (pud_val(*pud)) {

			if (!pud_large(*pud)) {

				last_map_addr = phys_pmd_update(pud, addr, end,

							 page_size_mask);

							 page_size_mask, prot);

				continue;

			}



			goto repeat_set_pte;

			/*

			 * If we are ok with PG_LEVEL_1G mapping, then we will

			 * use the existing mapping.

			 *

			 * Otherwise, we will split the gbpage mapping but use

			 * the same existing protection  bits except for large

			 * page, so that we don't violate Intel's TLB

			 * Application note (317080) which says, while changing

			 * the page sizes, new and old translations should

			 * not differ with respect to page frame and

			 * attributes.

			 */

			if (page_size_mask & (1 << PG_LEVEL_1G))

				continue;

			prot = pte_pgprot(pte_clrhuge(*(pte_t *)pud));

		}



		if (page_size_mask & (1<<PG_LEVEL_1G)) {

			pages++;

repeat_set_pte:

			spin_lock(&init_mm.page_table_lock);

			set_pte((pte_t *)pud,

				pfn_pte(addr >> PAGE_SHIFT, PAGE_KERNEL_LARGE));
@@ -430,7 +461,8 @@ repeat_set_pte: 
		}



		pmd = alloc_low_page(&pmd_phys);

		last_map_addr = phys_pmd_init(pmd, addr, end, page_size_mask);

		last_map_addr = phys_pmd_init(pmd, addr, end, page_size_mask,

					      prot);

		unmap_low_page(pmd);



		spin_lock(&init_mm.page_table_lock);
@@ -439,7 +471,6 @@ repeat_set_pte: 
	}

	__flush_tlb_all();



	if (physical_mapping_iter == 1)

	update_page_count(PG_LEVEL_1G, pages);



	return last_map_addr;
@@ -505,54 +536,15 @@ static void __init init_gbpages(void) 
		direct_gbpages = 0;

}



static int is_kernel(unsigned long pfn)

{

	unsigned long pg_addresss = pfn << PAGE_SHIFT;



	if (pg_addresss >= (unsigned long) __pa(_text) &&

	    pg_addresss < (unsigned long) __pa(_end))

		return 1;



	return 0;

}



static unsigned long __init kernel_physical_mapping_init(unsigned long start,

						unsigned long end,

						unsigned long page_size_mask)

{



	unsigned long next, last_map_addr;

	u64 cached_supported_pte_mask = __supported_pte_mask;

	unsigned long cache_start = start;

	unsigned long cache_end = end;



	/*

	 * First iteration will setup identity mapping using large/small pages

	 * based on page_size_mask, with other attributes same as set by

	 * the early code in head_64.S

	 *

	 * Second iteration will setup the appropriate attributes

	 * as desired for the kernel identity mapping.

	 *

	 * This two pass mechanism conforms to the TLB app note which says:

	 *

	 *     "Software should not write to a paging-structure entry in a way

	 *      that would change, for any linear address, both the page size

	 *      and either the page frame or attributes."

	 *

	 * For now, only difference between very early PTE attributes used in

	 * head_64.S and here is _PAGE_NX.

	 */

	BUILD_BUG_ON((__PAGE_KERNEL_LARGE & ~__PAGE_KERNEL_IDENT_LARGE_EXEC)

		     != _PAGE_NX);

	__supported_pte_mask &= ~(_PAGE_NX);

	physical_mapping_iter = 1;



repeat:

	last_map_addr = cache_end;

	unsigned long next, last_map_addr = end;



	start = (unsigned long)__va(cache_start);

	end = (unsigned long)__va(cache_end);

	start = (unsigned long)__va(start);

	end = (unsigned long)__va(end);



	for (; start < end; start = next) {

		pgd_t *pgd = pgd_offset_k(start);
@@ -564,21 +556,11 @@ repeat: 
			next = end;



		if (pgd_val(*pgd)) {

			/*

			 * Static identity mappings will be overwritten

			 * with run-time mappings. For example, this allows

			 * the static 0-1GB identity mapping to be mapped

			 * non-executable with this.

			 */

			if (is_kernel(pte_pfn(*((pte_t *) pgd))))

				goto realloc;



			last_map_addr = phys_pud_update(pgd, __pa(start),

						 __pa(end), page_size_mask);

			continue;

		}



realloc:

		pud = alloc_low_page(&pud_phys);

		last_map_addr = phys_pud_init(pud, __pa(start), __pa(next),

						 page_size_mask);
@@ -590,15 +572,6 @@ realloc: 
	}

	__flush_tlb_all();



	if (physical_mapping_iter == 1) {

		physical_mapping_iter = 2;

		/*

		 * Second iteration will set the actual desired PTE attributes.

		 */

		__supported_pte_mask = cached_supported_pte_mask;

		goto repeat;

	}



	return last_map_addr;

}

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