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

In the first pass, kernel physical mapping will be setup using large or
small pages but uses the same PTE attributes as that of the early
PTE attributes setup by early boot code in head_[32|64].S

After flushing TLB's, we go through the second pass, which setups the
direct mapped PTE's with the appropriate attributes (like NX, GLOBAL etc)
which are runtime detectable.

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."

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: arjan@linux.intel.com
Cc: venkatesh.pallipadi@intel.com
Cc: jeremy@goop.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 60 insertions, 5 deletions

diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
index d37f29376b0..9b5f7d7049d 100644
--- a/arch/x86/mm/init_32.c
+++ b/arch/x86/mm/init_32.c
@@ -194,11 +194,30 @@ static void __init kernel_physical_mapping_init(pgd_t *pgd_base,
 	pgd_t *pgd;
 	pmd_t *pmd;
 	pte_t *pte;
-	unsigned pages_2m = 0, pages_4k = 0;
+	unsigned pages_2m, pages_4k;
+	int mapping_iter;
+
+	/*
+	 * First iteration will setup identity mapping using large/small pages
+	 * based on use_pse, with other attributes same as set by
+	 * the early code in head_32.S
+	 *
+	 * Second iteration will setup the appropriate attributes (NX, GLOBAL..)
+	 * 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."
+	 */
+	mapping_iter = 1;
 
 	if (!cpu_has_pse)
 		use_pse = 0;
 
+repeat:
+	pages_2m = pages_4k = 0;
 	pfn = start_pfn;
 	pgd_idx = pgd_index((pfn<<PAGE_SHIFT) + PAGE_OFFSET);
 	pgd = pgd_base + pgd_idx;
@@ -224,6 +243,13 @@ static void __init kernel_physical_mapping_init(pgd_t *pgd_base,
 			if (use_pse) {
 				unsigned int addr2;
 				pgprot_t prot = PAGE_KERNEL_LARGE;
+				/*
+				 * first pass will use the same initial
+				 * identity mapping attribute + _PAGE_PSE.
+				 */
+				pgprot_t init_prot =
+					__pgprot(PTE_IDENT_ATTR |
+						 _PAGE_PSE);
 
 				addr2 = (pfn + PTRS_PER_PTE-1) * PAGE_SIZE +
 					PAGE_OFFSET + PAGE_SIZE-1;
@@ -233,7 +259,10 @@ static void __init kernel_physical_mapping_init(pgd_t *pgd_base,
 					prot = PAGE_KERNEL_LARGE_EXEC;
 
 				pages_2m++;
-				set_pmd(pmd, pfn_pmd(pfn, prot));
+				if (mapping_iter == 1)
+					set_pmd(pmd, pfn_pmd(pfn, init_prot));
+				else
+					set_pmd(pmd, pfn_pmd(pfn, prot));
 
 				pfn += PTRS_PER_PTE;
 				continue;
@@ -245,17 +274,43 @@ static void __init kernel_physical_mapping_init(pgd_t *pgd_base,
 			for (; pte_ofs < PTRS_PER_PTE && pfn < end_pfn;
 			     pte++, pfn++, pte_ofs++, addr += PAGE_SIZE) {
 				pgprot_t prot = PAGE_KERNEL;
+				/*
+				 * first pass will use the same initial
+				 * identity mapping attribute.
+				 */
+				pgprot_t init_prot = __pgprot(PTE_IDENT_ATTR);
 
 				if (is_kernel_text(addr))
 					prot = PAGE_KERNEL_EXEC;
 
 				pages_4k++;
-				set_pte(pte, pfn_pte(pfn, prot));
+				if (mapping_iter == 1)
+					set_pte(pte, pfn_pte(pfn, init_prot));
+				else
+					set_pte(pte, pfn_pte(pfn, prot));
 			}
 		}
 	}
-	update_page_count(PG_LEVEL_2M, pages_2m);
-	update_page_count(PG_LEVEL_4K, pages_4k);
+	if (mapping_iter == 1) {
+		/*
+		 * update direct mapping page count only in the first
+		 * iteration.
+		 */
+		update_page_count(PG_LEVEL_2M, pages_2m);
+		update_page_count(PG_LEVEL_4K, pages_4k);
+
+		/*
+		 * local global flush tlb, which will flush the previous
+		 * mappings present in both small and large page TLB's.
+		 */
+		__flush_tlb_all();
+
+		/*
+		 * Second iteration will set the actual desired PTE attributes.
+		 */
+		mapping_iter = 2;
+		goto repeat;
+	}
 }
 
 /*