KVM: arm64: Clarify explanation of STAGE2_PGTABLE_LEVELS

In attempting to re-construct the logic for our stage 2 page table
layout I found the reasoning in the comment explaining how we calculate
the number of levels used for stage 2 page tables a bit backwards.

This commit attempts to clarify the comment, to make it slightly easier
to read without having the Arm ARM open on the right page.

While we're at it, fixup a typo in a comment that was recently changed.
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm64/include/asm/stage2_pgtable.h

@@ -30,16 +30,14 @@
 #define pt_levels_pgdir_shift(lvls)	ARM64_HW_PGTABLE_LEVEL_SHIFT(4 - (lvls))
 
 /*
- * The hardware supports concatenation of up to 16 tables at stage2 entry level
- * and we use the feature whenever possible.
+ * The hardware supports concatenation of up to 16 tables at stage2 entry
+ * level and we use the feature whenever possible, which means we resolve 4
+ * additional bits of address at the entry level.
  *
- * Now, the minimum number of bits resolved at any level is (PAGE_SHIFT - 3).
- * On arm64, the smallest PAGE_SIZE supported is 4k, which means
- *             (PAGE_SHIFT - 3) > 4 holds for all page sizes.
- * This implies, the total number of page table levels at stage2 expected
- * by the hardware is actually the number of levels required for (IPA_SHIFT - 4)
- * in normal translations(e.g, stage1), since we cannot have another level in
- * the range (IPA_SHIFT, IPA_SHIFT - 4).
+ * This implies, the total number of page table levels required for
+ * IPA_SHIFT at stage2 expected by the hardware can be calculated using
+ * the same logic used for the (non-collapsable) stage1 page tables but for
+ * (IPA_SHIFT - 4).
  */
 #define stage2_pgtable_levels(ipa)	ARM64_HW_PGTABLE_LEVELS((ipa) - 4)
 #define kvm_stage2_levels(kvm)		VTCR_EL2_LVLS(kvm->arch.vtcr)

virt/kvm/arm/mmu.c

@@ -1356,7 +1356,7 @@ static bool transparent_hugepage_adjust(kvm_pfn_t *pfnp, phys_addr_t *ipap)
 	struct page *page = pfn_to_page(pfn);
 
 	/*
-	 * PageTransCompoungMap() returns true for THP and
+	 * PageTransCompoundMap() returns true for THP and
 	 * hugetlbfs. Make sure the adjustment is done only for THP
 	 * pages.
 	 */