ARC: mm: retire support for aliasing VIPT D$

Legacy ARC700 processors (first generation of MMU enabled ARC cores) had
VIPT cached which could be configured such that they could alias.
Corresponding support in kernel (with all the obnoxious cache flush overhead)
was added in ARC port 10 years ago to support 1 silicon. That is long bygone
and we can let it RIP.

Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Vineet Gupta <vgupta@kernel.org>

1 files changed, 6 insertions, 130 deletions

diff --git a/arch/arc/mm/cache.c b/arch/arc/mm/cache.c
index f7e05c146637..9106ceac323c 100644
--- a/arch/arc/mm/cache.c
+++ b/arch/arc/mm/cache.c
@@ -145,10 +145,9 @@ dc_chk:
 	p_dc->sz_k = 1 << (dbcr.sz - 1);
 
 	n += scnprintf(buf + n, len - n,
-			"D-Cache\t\t: %uK, %dway/set, %uB Line, %s%s%s\n",
+			"D-Cache\t\t: %uK, %dway/set, %uB Line, %s%s\n",
 			p_dc->sz_k, assoc, p_dc->line_len,
 			vipt ? "VIPT" : "PIPT",
-			p_dc->colors > 1 ? " aliasing" : "",
 			IS_USED_CFG(CONFIG_ARC_HAS_DCACHE));
 
 slc_chk:
@@ -703,51 +702,10 @@ static inline void arc_slc_enable(void)
  * Exported APIs
  */
 
-/*
- * Handle cache congruency of kernel and userspace mappings of page when kernel
- * writes-to/reads-from
- *
- * The idea is to defer flushing of kernel mapping after a WRITE, possible if:
- *  -dcache is NOT aliasing, hence any U/K-mappings of page are congruent
- *  -U-mapping doesn't exist yet for page (finalised in update_mmu_cache)
- *  -In SMP, if hardware caches are coherent
- *
- * There's a corollary case, where kernel READs from a userspace mapped page.
- * If the U-mapping is not congruent to K-mapping, former needs flushing.
- */
 void flush_dcache_folio(struct folio *folio)
 {
-	struct address_space *mapping;
-
-	if (!cache_is_vipt_aliasing()) {
-		clear_bit(PG_dc_clean, &folio->flags);
-		return;
-	}
-
-	/* don't handle anon pages here */
-	mapping = folio_flush_mapping(folio);
-	if (!mapping)
-		return;
-
-	/*
-	 * pagecache page, file not yet mapped to userspace
-	 * Make a note that K-mapping is dirty
-	 */
-	if (!mapping_mapped(mapping)) {
-		clear_bit(PG_dc_clean, &folio->flags);
-	} else if (folio_mapped(folio)) {
-		/* kernel reading from page with U-mapping */
-		phys_addr_t paddr = (unsigned long)folio_address(folio);
-		unsigned long vaddr = folio_pos(folio);
-
-		/*
-		 * vaddr is not actually the virtual address, but is
-		 * congruent to every user mapping.
-		 */
-		if (addr_not_cache_congruent(paddr, vaddr))
-			__flush_dcache_pages(paddr, vaddr,
-						folio_nr_pages(folio));
-	}
+	clear_bit(PG_dc_clean, &folio->flags);
+	return;
 }
 EXPORT_SYMBOL(flush_dcache_folio);
 
@@ -921,44 +879,6 @@ noinline void flush_cache_all(void)
 
 }
 
-#ifdef CONFIG_ARC_CACHE_VIPT_ALIASING
-
-void flush_cache_mm(struct mm_struct *mm)
-{
-	flush_cache_all();
-}
-
-void flush_cache_page(struct vm_area_struct *vma, unsigned long u_vaddr,
-		      unsigned long pfn)
-{
-	phys_addr_t paddr = pfn << PAGE_SHIFT;
-
-	u_vaddr &= PAGE_MASK;
-
-	__flush_dcache_pages(paddr, u_vaddr, 1);
-
-	if (vma->vm_flags & VM_EXEC)
-		__inv_icache_pages(paddr, u_vaddr, 1);
-}
-
-void flush_cache_range(struct vm_area_struct *vma, unsigned long start,
-		       unsigned long end)
-{
-	flush_cache_all();
-}
-
-void flush_anon_page(struct vm_area_struct *vma, struct page *page,
-		     unsigned long u_vaddr)
-{
-	/* TBD: do we really need to clear the kernel mapping */
-	__flush_dcache_pages((phys_addr_t)page_address(page), u_vaddr, 1);
-	__flush_dcache_pages((phys_addr_t)page_address(page),
-			    (phys_addr_t)page_address(page), 1);
-
-}
-
-#endif
-
 void copy_user_highpage(struct page *to, struct page *from,
 	unsigned long u_vaddr, struct vm_area_struct *vma)
 {
@@ -966,46 +886,11 @@ void copy_user_highpage(struct page *to, struct page *from,
 	struct folio *dst = page_folio(to);
 	void *kfrom = kmap_atomic(from);
 	void *kto = kmap_atomic(to);
-	int clean_src_k_mappings = 0;
-
-	/*
-	 * If SRC page was already mapped in userspace AND it's U-mapping is
-	 * not congruent with K-mapping, sync former to physical page so that
-	 * K-mapping in memcpy below, sees the right data
-	 *
-	 * Note that while @u_vaddr refers to DST page's userspace vaddr, it is
-	 * equally valid for SRC page as well
-	 *
-	 * For !VIPT cache, all of this gets compiled out as
-	 * addr_not_cache_congruent() is 0
-	 */
-	if (page_mapcount(from) && addr_not_cache_congruent(kfrom, u_vaddr)) {
-		__flush_dcache_pages((unsigned long)kfrom, u_vaddr, 1);
-		clean_src_k_mappings = 1;
-	}
 
 	copy_page(kto, kfrom);
 
-	/*
-	 * Mark DST page K-mapping as dirty for a later finalization by
-	 * update_mmu_cache(). Although the finalization could have been done
-	 * here as well (given that both vaddr/paddr are available).
-	 * But update_mmu_cache() already has code to do that for other
-	 * non copied user pages (e.g. read faults which wire in pagecache page
-	 * directly).
-	 */
 	clear_bit(PG_dc_clean, &dst->flags);
-
-	/*
-	 * if SRC was already usermapped and non-congruent to kernel mapping
-	 * sync the kernel mapping back to physical page
-	 */
-	if (clean_src_k_mappings) {
-		__flush_dcache_pages((unsigned long)kfrom,
-					(unsigned long)kfrom, 1);
-	} else {
-		clear_bit(PG_dc_clean, &src->flags);
-	}
+	clear_bit(PG_dc_clean, &src->flags);
 
 	kunmap_atomic(kto);
 	kunmap_atomic(kfrom);
@@ -1140,17 +1025,8 @@ static noinline void __init arc_cache_init_master(void)
 			      dc->line_len, L1_CACHE_BYTES);
 
 		/* check for D-Cache aliasing on ARCompact: ARCv2 has PIPT */
-		if (is_isa_arcompact()) {
-			int handled = IS_ENABLED(CONFIG_ARC_CACHE_VIPT_ALIASING);
-
-			if (dc->colors > 1) {
-				if (!handled)
-					panic("Enable CONFIG_ARC_CACHE_VIPT_ALIASING\n");
-				if (CACHE_COLORS_NUM != dc->colors)
-					panic("CACHE_COLORS_NUM not optimized for config\n");
-			} else if (handled && dc->colors == 1) {
-				panic("Disable CONFIG_ARC_CACHE_VIPT_ALIASING\n");
-			}
+		if (is_isa_arcompact() && dc->colors > 1) {
+			panic("Aliasing VIPT cache not supported\n");
 		}
 	}