FAILED: patch "[PATCH] Revert "x86/mm/ident_map: Use gbpages only where full GB page" failed to apply to 5.15-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x c567f2948f57bdc03ed03403ae0234085f376b7d
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@xxxxxxxxxxxxxxx>' --in-reply-to '2024040120-destiny-extenuate-257a@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

c567f2948f57 ("Revert "x86/mm/ident_map: Use gbpages only where full GB page should be mapped."")
0a845e0f6348 ("mm/treewide: replace pud_large() with pud_leaf()")
d794734c9bbf ("x86/mm/ident_map: Use gbpages only where full GB page should be mapped.")
27af67f35631 ("powerpc/book3s64/mm: enable transparent pud hugepage")
104c49d5b6dc ("powerpc/mm/trace: convert trace event to trace event class")
040ec6202bb8 ("powerpc/mm/book3s64: Use pmdp_ptep helper instead of typecasting.")
bb1520d581a3 ("s390/mm: start kernel with DAT enabled")
9c3205b2b062 ("s390/boot: cleanup decompressor header files")
47477c84b891 ("Merge tag 's390-6.2-1' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From c567f2948f57bdc03ed03403ae0234085f376b7d Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@xxxxxxxxxx>
Date: Mon, 25 Mar 2024 11:47:51 +0100
Subject: [PATCH] Revert "x86/mm/ident_map: Use gbpages only where full GB page
 should be mapped."

This reverts commit d794734c9bbfe22f86686dc2909c25f5ffe1a572.

While the original change tries to fix a bug, it also unintentionally broke
existing systems, see the regressions reported at:

  https://lore.kernel.org/all/3a1b9909-45ac-4f97-ad68-d16ef1ce99db@xxxxxxxxxxxxxxx/

Since d794734c9bbf was also marked for -stable, let's back it out before
causing more damage.

Note that due to another upstream change the revert was not 100% automatic:

  0a845e0f6348 mm/treewide: replace pud_large() with pud_leaf()

Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Cc: Russ Anderson <rja@xxxxxxx>
Cc: Steve Wahl <steve.wahl@xxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/all/3a1b9909-45ac-4f97-ad68-d16ef1ce99db@xxxxxxxxxxxxxxx/
Fixes: d794734c9bbf ("x86/mm/ident_map: Use gbpages only where full GB page should be mapped.")

diff --git a/arch/x86/mm/ident_map.c b/arch/x86/mm/ident_map.c
index a204a332c71f..968d7005f4a7 100644
--- a/arch/x86/mm/ident_map.c
+++ b/arch/x86/mm/ident_map.c
@@ -26,31 +26,18 @@ static int ident_pud_init(struct x86_mapping_info *info, pud_t *pud_page,
 	for (; addr < end; addr = next) {
 		pud_t *pud = pud_page + pud_index(addr);
 		pmd_t *pmd;
-		bool use_gbpage;
 
 		next = (addr & PUD_MASK) + PUD_SIZE;
 		if (next > end)
 			next = end;
 
-		/* if this is already a gbpage, this portion is already mapped */
-		if (pud_leaf(*pud))
-			continue;
-
-		/* Is using a gbpage allowed? */
-		use_gbpage = info->direct_gbpages;
-
-		/* Don't use gbpage if it maps more than the requested region. */
-		/* at the begining: */
-		use_gbpage &= ((addr & ~PUD_MASK) == 0);
-		/* ... or at the end: */
-		use_gbpage &= ((next & ~PUD_MASK) == 0);
-
-		/* Never overwrite existing mappings */
-		use_gbpage &= !pud_present(*pud);
-
-		if (use_gbpage) {
+		if (info->direct_gbpages) {
 			pud_t pudval;
 
+			if (pud_present(*pud))
+				continue;
+
+			addr &= PUD_MASK;
 			pudval = __pud((addr - info->offset) | info->page_flag);
 			set_pud(pud, pudval);
 			continue;