x86/mm/encrypt: Simplify sme_pgtable_calc()

sme_pgtable_calc() is unnecessary complex. It can be re-written in a
more stream-lined way.

As a side effect, we would get the code ready to boot-time switching
between paging modes.

Tested-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20180131135404.40692-4-kirill.shutemov@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/mm/mem_encrypt_identity.c

@@ -231,8 +231,7 @@ static void __init sme_map_range_decrypted_wp(struct sme_populate_pgd_data *ppd)
 
 static unsigned long __init sme_pgtable_calc(unsigned long len)
 {
-	unsigned long p4d_size, pud_size, pmd_size, pte_size;
-	unsigned long total;
+	unsigned long entries = 0, tables = 0;
 
 	/*
 	 * Perform a relatively simplistic calculation of the pagetable
@@ -246,42 +245,25 @@ static unsigned long __init sme_pgtable_calc(unsigned long len)
 	 * Incrementing the count for each covers the case where the addresses
 	 * cross entries.
 	 */
-	if (IS_ENABLED(CONFIG_X86_5LEVEL)) {
-		p4d_size = (ALIGN(len, PGDIR_SIZE) / PGDIR_SIZE) + 1;
-		p4d_size *= sizeof(p4d_t) * PTRS_PER_P4D;
-		pud_size = (ALIGN(len, P4D_SIZE) / P4D_SIZE) + 1;
-		pud_size *= sizeof(pud_t) * PTRS_PER_PUD;
-	} else {
-		p4d_size = 0;
-		pud_size = (ALIGN(len, PGDIR_SIZE) / PGDIR_SIZE) + 1;
-		pud_size *= sizeof(pud_t) * PTRS_PER_PUD;
-	}
-	pmd_size = (ALIGN(len, PUD_SIZE) / PUD_SIZE) + 1;
-	pmd_size *= sizeof(pmd_t) * PTRS_PER_PMD;
-	pte_size = 2 * sizeof(pte_t) * PTRS_PER_PTE;
 
-	total = p4d_size + pud_size + pmd_size + pte_size;
+	/* PGDIR_SIZE is equal to P4D_SIZE on 4-level machine. */
+	if (PTRS_PER_P4D > 1)
+		entries += (DIV_ROUND_UP(len, PGDIR_SIZE) + 1) * sizeof(p4d_t) * PTRS_PER_P4D;
+	entries += (DIV_ROUND_UP(len, P4D_SIZE) + 1) * sizeof(pud_t) * PTRS_PER_PUD;
+	entries += (DIV_ROUND_UP(len, PUD_SIZE) + 1) * sizeof(pmd_t) * PTRS_PER_PMD;
+	entries += 2 * sizeof(pte_t) * PTRS_PER_PTE;
 
 	/*
 	 * Now calculate the added pagetable structures needed to populate
 	 * the new pagetables.
 	 */
-	if (IS_ENABLED(CONFIG_X86_5LEVEL)) {
-		p4d_size = ALIGN(total, PGDIR_SIZE) / PGDIR_SIZE;
-		p4d_size *= sizeof(p4d_t) * PTRS_PER_P4D;
-		pud_size = ALIGN(total, P4D_SIZE) / P4D_SIZE;
-		pud_size *= sizeof(pud_t) * PTRS_PER_PUD;
-	} else {
-		p4d_size = 0;
-		pud_size = ALIGN(total, PGDIR_SIZE) / PGDIR_SIZE;
-		pud_size *= sizeof(pud_t) * PTRS_PER_PUD;
-	}
-	pmd_size = ALIGN(total, PUD_SIZE) / PUD_SIZE;
-	pmd_size *= sizeof(pmd_t) * PTRS_PER_PMD;
 
-	total += p4d_size + pud_size + pmd_size;
+	if (PTRS_PER_P4D > 1)
+		tables += DIV_ROUND_UP(entries, PGDIR_SIZE) * sizeof(p4d_t) * PTRS_PER_P4D;
+	tables += DIV_ROUND_UP(entries, P4D_SIZE) * sizeof(pud_t) * PTRS_PER_PUD;
+	tables += DIV_ROUND_UP(entries, PUD_SIZE) * sizeof(pmd_t) * PTRS_PER_PMD;
 
-	return total;
+	return entries + tables;
 }
 
 void __init __nostackprotector sme_encrypt_kernel(struct boot_params *bp)