parisc: Fix flush_anon_page on PA8800/PA8900

Anonymous pages are allocated with the shared mappings colouring,
SHM_COLOUR. Since the alias boundary on machines with PA8800 and
PA8900 processors is unknown, flush_user_cache_page() might not
flush all mappings of a shared anonymous page. Flushing the whole
data cache flushes all mappings.

This won't fix all coherency issues with shared mappings but it
seems to work well in practice.  I haven't seen any random memory
faults in almost a month on a rp3440 running as a debian buildd
machine.

There is a small preformance hit.

Signed-off-by: John David Anglin <dave.anglin@bell.net>
Signed-off-by: Helge Deller <deller@gmx.de>
Cc: stable@vger.kernel.org   # v5.18+

diff --git a/arch/parisc/kernel/cache.c b/arch/parisc/kernel/cache.c
index c8a11fc..a9bc578 100644 (file)
--- a/arch/parisc/kernel/cache.c
+++ b/arch/parisc/kernel/cache.c
@@ -722,7 +722,10 @@ void flush_anon_page(struct vm_area_struct *vma, struct page *page, unsigned lon
                return;
 
        if (parisc_requires_coherency()) {
-               flush_user_cache_page(vma, vmaddr);
+               if (vma->vm_flags & VM_SHARED)
+                       flush_data_cache();
+               else
+                       flush_user_cache_page(vma, vmaddr);
                return;
        }