CVE-2022-49172

In the Linux kernel, the following vulnerability has been resolved:

parisc: Fix non-access data TLB cache flush faults

When a page is not present, we get non-access data TLB faults from the fdc and fic instructions in flushuserdcacherangeasm and flushusericacherangeasm. When these occur, the cache line is not invalidated and potentially we get memory corruption. The problem was hidden by the nullification of the flush instructions.

These faults also affect performance. With pa8800/pa8900 processors, there will be 32 faults per 4 KB page since the cache line is 128 bytes. There will be more faults with earlier processors.

The problem is fixed by using flushcachepages(). It does the flush using a tmp alias mapping.

The flushcachepages() call in flushcacherange() flushed too large a range.

V2: Remove unnecessary preemptdisable() and preemptenable() calls.