[PATCH v2 08/23] parisc: add pte_unmap() to balance get_ptep()

From: Hugh Dickins <hughd@google•com>
To: Andrew Morton <akpm@linux-foundation•org>
Cc: Mike Kravetz <mike.kravetz@oracle•com>,
	Mike Rapoport <rppt@kernel•org>,
	 "Kirill A. Shutemov" <kirill.shutemov@linux•intel.com>,
	 Matthew Wilcox <willy@infradead•org>,
	David Hildenbrand <david@redhat•com>,
	 Suren Baghdasaryan <surenb@google•com>,
	 Qi Zheng <zhengqi.arch@bytedance•com>,
	 Peter Zijlstra <peterz@infradead•org>,
	 Russell King <linux@armlinux•org.uk>,
	 Catalin Marinas <catalin.marinas@arm•com>,
	Will Deacon <will@kernel•org>,
	 Geert Uytterhoeven <geert@linux-m68k•org>,
	 Greg Ungerer <gerg@linux-m68k•org>,
	Michal Simek <monstr@monstr•eu>,
	 Thomas Bogendoerfer <tsbogend@alpha•franken.de>,
	 Helge Deller <deller@gmx•de>,
	John David Anglin <dave.anglin@bell•net>,
	 "Aneesh Kumar K.V" <aneesh.kumar@linux•ibm.com>,
	 Michael Ellerman <mpe@ellerman•id.au>,
	 Alexandre Ghiti <alexghiti@rivosinc•com>,
	 Palmer Dabbelt <palmer@dabbelt•com>,
	Heiko Carstens <hca@linux•ibm.com>,
	 Christian Borntraeger <borntraeger@linux•ibm.com>,
	 Claudio Imbrenda <imbrenda@linux•ibm.com>,
	 Alexander Gordeev <agordeev@linux•ibm.com>,
	 John Paul Adrian Glaubitz <glaubitz@physik•fu-berlin.de>,
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	 Max Filippov <jcmvbkbc@gmail•com>,
	x86@kernel•org,  linux-arm-kernel@lists•infradead.org,
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	linux-mips@vger•kernel.org,  linux-parisc@vger•kernel.org,
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	linux-mm@kvack•org
Subject: [PATCH v2 08/23] parisc: add pte_unmap() to balance get_ptep()
Date: Thu, 8 Jun 2023 12:18:35 -0700 (PDT)	[thread overview]
Message-ID: <653369-95ef-acd2-d6ea-e95f5a997493@google.com> (raw)
In-Reply-To: <a4963be9-7aa6-350-66d0-2ba843e1af44@google.com>

To keep balance in future, remember to pte_unmap() after a successful
get_ptep().  And act as if flush_cache_pages() really needs a map there,
to read the pfn before "unmapping", to be sure page table is not removed.

Signed-off-by: Hugh Dickins <hughd@google•com>
---
 arch/parisc/kernel/cache.c | 26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/arch/parisc/kernel/cache.c b/arch/parisc/kernel/cache.c
index ca4a302d4365..501160250bb7 100644
--- a/arch/parisc/kernel/cache.c
+++ b/arch/parisc/kernel/cache.c
@@ -426,10 +426,15 @@ void flush_dcache_page(struct page *page)
 		offset = (pgoff - mpnt->vm_pgoff) << PAGE_SHIFT;
 		addr = mpnt->vm_start + offset;
 		if (parisc_requires_coherency()) {
+			bool needs_flush = false;
 			pte_t *ptep;
 
 			ptep = get_ptep(mpnt->vm_mm, addr);
-			if (ptep && pte_needs_flush(*ptep))
+			if (ptep) {
+				needs_flush = pte_needs_flush(*ptep);
+				pte_unmap(ptep);
+			}
+			if (needs_flush)
 				flush_user_cache_page(mpnt, addr);
 		} else {
 			/*
@@ -561,14 +566,20 @@ EXPORT_SYMBOL(flush_kernel_dcache_page_addr);
 static void flush_cache_page_if_present(struct vm_area_struct *vma,
 	unsigned long vmaddr, unsigned long pfn)
 {
-	pte_t *ptep = get_ptep(vma->vm_mm, vmaddr);
+	bool needs_flush = false;
+	pte_t *ptep;
 
 	/*
 	 * The pte check is racy and sometimes the flush will trigger
 	 * a non-access TLB miss. Hopefully, the page has already been
 	 * flushed.
 	 */
-	if (ptep && pte_needs_flush(*ptep))
+	ptep = get_ptep(vma->vm_mm, vmaddr);
+	if (ptep) {
+		needs_flush = pte_needs_flush(*ptep);
+		pte_unmap(ptep);
+	}
+	if (needs_flush)
 		flush_cache_page(vma, vmaddr, pfn);
 }
 
@@ -635,17 +646,22 @@ static void flush_cache_pages(struct vm_area_struct *vma, unsigned long start, u
 	pte_t *ptep;
 
 	for (addr = start; addr < end; addr += PAGE_SIZE) {
+		bool needs_flush = false;
 		/*
 		 * The vma can contain pages that aren't present. Although
 		 * the pte search is expensive, we need the pte to find the
 		 * page pfn and to check whether the page should be flushed.
 		 */
 		ptep = get_ptep(vma->vm_mm, addr);
-		if (ptep && pte_needs_flush(*ptep)) {
+		if (ptep) {
+			needs_flush = pte_needs_flush(*ptep);
+			pfn = pte_pfn(*ptep);
+			pte_unmap(ptep);
+		}
+		if (needs_flush) {
 			if (parisc_requires_coherency()) {
 				flush_user_cache_page(vma, addr);
 			} else {
-				pfn = pte_pfn(*ptep);
 				if (WARN_ON(!pfn_valid(pfn)))
 					return;
 				__flush_cache_page(vma, addr, PFN_PHYS(pfn));
-- 
2.35.3


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