parisc: Flush kernel data mapping in set_pte_at() when installing pte for user page

For years, there have been random segmentation faults in userspace on
SMP PA-RISC machines.  It occurred to me that this might be a problem in
set_pte_at().  MIPS and some other architectures do cache flushes when
installing PTEs with the present bit set.

Here I have adapted the code in update_mmu_cache() to flush the kernel
mapping when the kernel flush is deferred, or when the kernel mapping
may alias with the user mapping.  This simplifies calls to
update_mmu_cache().

I also changed the barrier in set_pte() from a compiler barrier to a
full memory barrier.  I know this change is not sufficient to fix the
problem.  It might not be needed.

I have had a few days of operation with 5.14.16 to 5.15.1 and haven't
seen any random segmentation faults on rp3440 or c8000 so far.
Signed-off-by: John David Anglin <dave.anglin@bell.net>
Signed-off-by: Helge Deller <deller@gmx.de>
Cc: stable@kernel.org # 5.12+

arch/parisc/include/asm/pgtable.h

@@ -76,6 +76,8 @@ static inline void purge_tlb_entries(struct mm_struct *mm, unsigned long addr)
 	purge_tlb_end(flags);
 }
 
+extern void __update_cache(pte_t pte);
+
 /* Certain architectures need to do special things when PTEs
  * within a page table are directly modified.  Thus, the following
  * hook is made available.
@@ -83,11 +85,14 @@ static inline void purge_tlb_entries(struct mm_struct *mm, unsigned long addr)
 #define set_pte(pteptr, pteval)			\
 	do {					\
 		*(pteptr) = (pteval);		\
-		barrier();			\
+		mb();				\
 	} while(0)
 
 #define set_pte_at(mm, addr, pteptr, pteval)	\
 	do {					\
+		if (pte_present(pteval) &&	\
+		    pte_user(pteval))		\
+			__update_cache(pteval);	\
 		*(pteptr) = (pteval);		\
 		purge_tlb_entries(mm, addr);	\
 	} while (0)
@@ -303,6 +308,7 @@ extern unsigned long *empty_zero_page;
 
 #define pte_none(x)     (pte_val(x) == 0)
 #define pte_present(x)	(pte_val(x) & _PAGE_PRESENT)
+#define pte_user(x)	(pte_val(x) & _PAGE_USER)
 #define pte_clear(mm, addr, xp)  set_pte_at(mm, addr, xp, __pte(0))
 
 #define pmd_flag(x)	(pmd_val(x) & PxD_FLAG_MASK)
@@ -410,7 +416,7 @@ extern void paging_init (void);
 
 #define PG_dcache_dirty         PG_arch_1
 
-extern void update_mmu_cache(struct vm_area_struct *, unsigned long, pte_t *);
+#define update_mmu_cache(vms,addr,ptep) __update_cache(*ptep)
 
 /* Encode and de-code a swap entry */
 

arch/parisc/kernel/cache.c

@@ -83,9 +83,9 @@ EXPORT_SYMBOL(flush_cache_all_local);
 #define pfn_va(pfn)	__va(PFN_PHYS(pfn))
 
 void
-update_mmu_cache(struct vm_area_struct *vma, unsigned long address, pte_t *ptep)
+__update_cache(pte_t pte)
 {
-	unsigned long pfn = pte_pfn(*ptep);
+	unsigned long pfn = pte_pfn(pte);
 	struct page *page;
 
 	/* We don't have pte special.  As a result, we can be called with