Re: [linuxsh-dev] Unaligned access crash in signal handlers

[NIIBE Y. <gn...@m1...>]

SUGIOKA Toshinobu wrote:
 > Currently flush_icache_range uses A-bit. but A-bit works only when
 > ITLB entry exists. UTLB entry should not work.
 > So every I-cache entry should be compared with physical address by hand
 > or all I-cache should be invalidated.

Umm...  I didn't know that.  I've checked the hardware manual, and
you're right.  We need ITLB entry to flush I-cache with A-bit.

While The Right Thing may be fixing flush_icache_range, I'm not sure
about the semantics well, right now.  It seems for me that we don't
need to purge out the I-cache, but just write back D-cache, with newer
scheme (Documentation/cachetlb.txt), but I'm not sure.

Besides, currently, the arguments (START, END) to flush_icache_range
is large one (i.e. mmap ranges) except signal handling, so we need to
re-write the function anyway.

Could you please try this out?  This purges the entry regardless it's
the page mapped or not.

This also includes a bug fix of SH-3 shared page.  X server worked
quite badly in SH-3 implementation because of that.


2001-01-23  NIIBE Yutaka  <gn...@m1...>

	* arch/sh/kernel/signal.c (setup_frame, setup_rt_frame): 
	Use flush_cache_sigtramp.

	* arch/sh/mm/cache.c (flush_cache_sigtramp): Implemented.

	* include/asm-sh/pgtable.h (_PAGE_SHARED): Always _PAGE_U0_SHARED.
	(was conditionally _PAGE_HW_SHARED on SH-3).  With _PAGE_HW_SHARED,
	all processes share the page, while proper semantics is "some
	processes share the page".
	(flush_cache_sigtramp): New function.

Index: arch/sh/kernel/signal.c
===================================================================
RCS file: /cvsroot/linuxsh/kernel/arch/sh/kernel/signal.c,v
retrieving revision 1.13
diff -u -r1.13 signal.c
--- arch/sh/kernel/signal.c	2000/09/04 06:41:45	1.13
+++ arch/sh/kernel/signal.c	2001/01/23 07:46:38
@@ -433,7 +433,7 @@
 		current->comm, current->pid, frame, regs->pc, regs->pr);
 #endif
 
-	flush_icache_range(regs->pr, regs->pr+4);
+	flush_cache_sigtramp(regs->pr);
 	return;
 
 give_sigsegv:
@@ -507,7 +507,7 @@
 		current->comm, current->pid, frame, regs->pc, regs->pr);
 #endif
 
-	flush_icache_range(regs->pr, regs->pr+4);
+	flush_cache_sigtramp(regs->pr);
 	return;
 
 give_sigsegv:
Index: arch/sh/mm/cache.c
===================================================================
RCS file: /cvsroot/linuxsh/kernel/arch/sh/mm/cache.c,v
retrieving revision 1.21
diff -u -r1.21 cache.c
--- arch/sh/mm/cache.c	2000/09/18 05:15:35	1.21
+++ arch/sh/mm/cache.c	2001/01/23 07:46:38
@@ -244,6 +244,22 @@
 }
 
 /*
+ * Write back the D-cache and purge the I-cache for signal trampoline. 
+ */
+void flush_cache_sigtramp(unsigned long addr)
+{
+	unsigned long v, index;
+
+	v = addr & ~(L1_CACHE_BYTES-1);
+	asm volatile("ocbwb	%0"
+		     : /* no output */
+		     : "m" (__m(v)));
+
+	index = CACHE_IC_ADDRESS_ARRAY| (v&CACHE_IC_ENTRY_MASK);
+	ctrl_outl(0, index);	/* Clear out Valid-bit */
+}
+
+/*
  * Invalidate the I-cache of the page (don't need to write back D-cache).
  *
  * Called from kernel/ptrace.c, mm/memory.c after flush_page_to_ram is called.
Index: include/asm-sh/pgtable.h
===================================================================
RCS file: /cvsroot/linuxsh/kernel/include/asm-sh/pgtable.h,v
retrieving revision 1.16
diff -u -r1.16 pgtable.h
--- include/asm-sh/pgtable.h	2000/11/22 07:05:18	1.16
+++ include/asm-sh/pgtable.h	2001/01/23 07:46:41
@@ -39,6 +39,7 @@
 #define flush_dcache_page(page)			do { } while (0)
 #define flush_icache_range(start, end)		do { } while (0)
 #define flush_icache_page(vma,pg)		do { } while (0)
+#define flush_cache_sigtramp(vaddr)		do { } while (0)
 #elif defined(__SH4__)
 /*
  *  Caches are broken on SH-4, so we need them.
@@ -52,6 +53,7 @@
 extern void flush_dcache_page(struct page *pg);
 extern void flush_icache_range(unsigned long start, unsigned long end);
 extern void flush_icache_page(struct vm_area_struct *vma, struct page *pg);
+extern void flush_cache_sigtramp(unsigned long addr);
 #endif
 
 /*
@@ -125,11 +127,7 @@
 /* Hardware flags: SZ=1 (4k-byte) */
 #define _PAGE_FLAGS_HARD		0x00000010
 
-#if defined(__sh3__)
-#define _PAGE_SHARED	_PAGE_HW_SHARED
-#elif defined(__SH4__)
 #define _PAGE_SHARED	_PAGE_U0_SHARED
-#endif
 
 #define _PAGE_TABLE	(_PAGE_PRESENT | _PAGE_RW | _PAGE_USER | _PAGE_ACCESSED | _PAGE_DIRTY)
 #define _KERNPG_TABLE	(_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED | _PAGE_DIRTY)
--