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From:   Thomas Gleixner <tglx@linutronix.de>
To:     LKML <linux-kernel@vger.kernel.org>
Cc:     vtolkm@googlemail.com, Andrew Morton <akpm@linux-foundation.org>,
        linux-mm@kvack.org,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>
Subject: [PATCH] mm/highmem: Take kmap_high_get() properly into account
Date:   Thu, 12 Nov 2020 11:59:32 +0100
Message-ID: <87y2j6n8mj.fsf@nanos.tec.linutronix.de>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

kunmap_local() warns when the virtual address to unmap is below
PAGE_OFFSET. This is correct except for the case that the mapping was
obtained via kmap_high_get() because the PKMAP addresses are right below
PAGE_OFFSET.

Cure it by skipping the WARN_ON() when the unmap was handled by
kunmap_high().

Fixes: 298fa1ad5571 ("highmem: Provide generic variant of kmap_atomic*")
Reported-by: vtolkm@googlemail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 mm/highmem.c |   19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -426,12 +426,15 @@ static inline void *arch_kmap_local_high
 #endif
 
 /* Unmap a local mapping which was obtained by kmap_high_get() */
-static inline void kmap_high_unmap_local(unsigned long vaddr)
+static inline bool kmap_high_unmap_local(unsigned long vaddr)
 {
 #ifdef ARCH_NEEDS_KMAP_HIGH_GET
-	if (vaddr >= PKMAP_ADDR(0) && vaddr < PKMAP_ADDR(LAST_PKMAP))
+	if (vaddr >= PKMAP_ADDR(0) && vaddr < PKMAP_ADDR(LAST_PKMAP)) {
 		kunmap_high(pte_page(pkmap_page_table[PKMAP_NR(vaddr)]));
+		return true;
+	}
 #endif
+	return false;
 }
 
 static inline int kmap_local_calc_idx(int idx)
@@ -491,10 +494,14 @@ void kunmap_local_indexed(void *vaddr)
 
 	if (addr < __fix_to_virt(FIX_KMAP_END) ||
 	    addr > __fix_to_virt(FIX_KMAP_BEGIN)) {
-		WARN_ON_ONCE(addr < PAGE_OFFSET);
-
-		/* Handle mappings which were obtained by kmap_high_get() */
-		kmap_high_unmap_local(addr);
+		/*
+		 * Handle mappings which were obtained by kmap_high_get()
+		 * first as the virtual address of such mappings is below
+		 * PAGE_OFFSET. Warn for all other addresses which are in
+		 * the user space part of the virtual address space.
+		 */
+		if (!kmap_high_unmap_local(addr))
+			WARN_ON_ONCE(addr < PAGE_OFFSET);
 		return;
 	}