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

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On 6/8/23 21:18, Hugh Dickins wrote:
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@xxxxxxxxxx>

For the parisc parts:

Acked-by: Helge Deller <deller@xxxxxx> # parisc

Helge


---
  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));





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