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From:   Christophe Leroy <christophe.leroy@c-s.fr>
Subject: [PATCH 2/2] powerpc/8xx: Make 8M hugepages also compatible with the
 512K pages slice
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        aneesh.kumar@linux.ibm.com
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Date:   Thu,  6 Feb 2020 19:21:55 +0000 (UTC)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 8xx, slices are used because hugepages (512k or 8M) and small
pages (4k or 16k) cannot share the same PGD entry. However, as 8M
entirely covers two PGD entries (One PGD entry covers 4M), there
will implicitely be no conflict between 8M pages and any other size.
So 8M is also compatible with the 512K page slices as well.

Handle 512K page slices as fallback compat mask for 8M pages.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 arch/powerpc/mm/slice.c | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c
index dffe1a45b6ed..cb5b532d3d48 100644
--- a/arch/powerpc/mm/slice.c
+++ b/arch/powerpc/mm/slice.c
@@ -422,6 +422,8 @@ static inline void slice_andnot_mask(struct slice_mask *dst,
 
 #ifdef CONFIG_PPC_64K_PAGES
 #define MMU_PAGE_BASE	MMU_PAGE_64K
+#elif defined(CONFIG_PPC_16K_PAGES)
+#define MMU_PAGE_BASE	MMU_PAGE_16K
 #else
 #define MMU_PAGE_BASE	MMU_PAGE_4K
 #endif
@@ -514,9 +516,19 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
 	 * If we support combo pages, we can allow 64k pages in 4k slices
 	 * The mask copies could be avoided in most cases here if we had
 	 * a pointer to good mask for the next code to use.
+	 *
+	 * On 8xx, slices are used because hugepages (512k or 8M) and small
+	 * pages (4k or 16k) cannot share the same PGD entry. However, as 8M
+	 * entirely covers two PGD entries, there will implicitely be no
+	 * conflict between 8M pages and any other size. So 8M is compatible
+	 * with the 512k page slice as well.
 	 */
-	if (IS_ENABLED(CONFIG_PPC_64K_PAGES) && psize == MMU_PAGE_64K) {
-		compat_maskp = slice_mask_for_size(&mm->context, MMU_PAGE_4K);
+	if ((IS_ENABLED(CONFIG_PPC_64K_PAGES) && psize == MMU_PAGE_64K) ||
+	    (IS_ENABLED(CONFIG_PPC_8xx) && psize == MMU_PAGE_8M)) {
+		if (IS_ENABLED(CONFIG_PPC_8xx))
+			compat_maskp = slice_mask_for_size(&mm->context, MMU_PAGE_512K);
+		else
+			compat_maskp = slice_mask_for_size(&mm->context, MMU_PAGE_4K);
 		if (fixed)
 			slice_or_mask(&good_mask, maskp, compat_maskp);
 		else
@@ -593,9 +605,8 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
 	newaddr = slice_find_area(mm, len, &potential_mask,
 				  psize, topdown, high_limit);
 
-	if (IS_ENABLED(CONFIG_PPC_64K_PAGES) && newaddr == -ENOMEM &&
-	    psize == MMU_PAGE_64K) {
-		/* retry the search with 4k-page slices included */
+	if (compat_maskp && newaddr == -ENOMEM) {
+		/* retry the search with compatible slices included */
 		slice_or_mask(&potential_mask, &potential_mask, compat_maskp);
 		newaddr = slice_find_area(mm, len, &potential_mask,
 					  psize, topdown, high_limit);
@@ -767,12 +778,16 @@ int slice_is_hugepage_only_range(struct mm_struct *mm, unsigned long addr,
 
 	maskp = slice_mask_for_size(&mm->context, psize);
 
-	/* We need to account for 4k slices too */
-	if (IS_ENABLED(CONFIG_PPC_64K_PAGES) && psize == MMU_PAGE_64K) {
+	/* We need to account for compatible slices too */
+	if ((IS_ENABLED(CONFIG_PPC_64K_PAGES) && psize == MMU_PAGE_64K) ||
+	    (IS_ENABLED(CONFIG_PPC_8xx) && psize == MMU_PAGE_8M)) {
 		const struct slice_mask *compat_maskp;
 		struct slice_mask available;
 
-		compat_maskp = slice_mask_for_size(&mm->context, MMU_PAGE_4K);
+		if (IS_ENABLED(CONFIG_PPC_8xx))
+			compat_maskp = slice_mask_for_size(&mm->context, MMU_PAGE_512K);
+		else
+			compat_maskp = slice_mask_for_size(&mm->context, MMU_PAGE_4K);
 		slice_or_mask(&available, maskp, compat_maskp);
 		return !slice_check_range_fits(mm, &available, addr, len);
 	}
-- 
2.25.0