powerpc, mm: Fix mprotect on book3s 32-bit

On 32-bit book3s with hash-MMUs, tlb_flush() was a no-op. This was
unnoticed because all uses until recently were for unmaps, and thus
handled by __tlb_remove_tlb_entry().

After commit 4a18419f71cd ("mm/mprotect: use mmu_gather") in kernel 5.19,
tlb_gather_mmu() started being used for mprotect as well. This caused
mprotect to simply not work on these machines:

int *ptr = mmap(NULL, 4096, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
*ptr = 1; // force HPTE to be created
mprotect(ptr, 4096, PROT_READ);
*ptr = 2; // should segfault, but succeeds

Fixed by making tlb_flush() actually flush TLB pages. This finally
agrees with the behaviour of boot3s64's tlb_flush().

Fixes: 4a18419f71cd ("mm/mprotect: use mmu_gather")
Cc: [e-mail]
Reviewed-by: Christophe Leroy <[e-mail]>
Reviewed-by: Ritesh Harjani (IBM) <[e-mail]>
Signed-off-by: Dave Vasilevsky <[e-mail]>
Signed-off-by: Madhavan Srinivasan <[e-mail]>
Link: https://patch.msgid.link/[e-mail]

arch/powerpc/include/asm/book3s/32/tlbflush.h

···
 void hash__flush_tlb_mm(struct mm_struct *mm);
 void hash__flush_tlb_page(struct vm_area_struct *vma, unsigned long vmaddr);
 void hash__flush_range(struct mm_struct *mm, unsigned long start, unsigned long end);
+void hash__flush_gather(struct mmu_gather *tlb);
 
 #ifdef CONFIG_SMP
 void _tlbie(unsigned long address);
···
 static inline void tlb_flush(struct mmu_gather *tlb)
 {
 	/* 603 needs to flush the whole TLB here since it doesn't use a hash table. */
-	if (!mmu_has_feature(MMU_FTR_HPTE_TABLE))
+	if (mmu_has_feature(MMU_FTR_HPTE_TABLE))
+		hash__flush_gather(tlb);
+	else
 		_tlbia();
 }
 

arch/powerpc/mm/book3s32/tlb.c

···
 		flush_hash_pages(mm->context.id, vmaddr, pmd_val(*pmd), 1);
 }
 EXPORT_SYMBOL(hash__flush_tlb_page);
+
+void hash__flush_gather(struct mmu_gather *tlb)
+{
+	if (tlb->fullmm || tlb->need_flush_all)
+		hash__flush_tlb_mm(tlb->mm);
+	else
+		hash__flush_range(tlb->mm, tlb->start, tlb->end);
+}
+EXPORT_SYMBOL(hash__flush_gather);