Here is an patch to fix virtual aliasing problem with SysV IPC shared
memory. I tested this patch on a r4k cpu with 32Kb D-cache.
If D-cache is smaller than PAGE_SIZE this patch is not needed at all,
but I think it is not so bad unconditionally forcing alignment to
SHMLBA.
---
Atsushi Nemoto
diff -ur linux.sgi/arch/mips/kernel/syscall.c linux/arch/mips/kernel/syscall.c
--- linux.sgi/arch/mips/kernel/syscall.c Thu Apr 5 13:56:09 2001
+++ linux/arch/mips/kernel/syscall.c Mon Aug 6 16:16:36 2001
@@ -30,6 +30,7 @@
#include <asm/signal.h>
#include <asm/stackframe.h>
#include <asm/uaccess.h>
+#include <asm/shmparam.h>
extern asmlinkage void syscall_trace(void);
typedef asmlinkage int (*syscall_t)(void *a0,...);
@@ -91,6 +92,47 @@
{
return do_mmap2(addr, len, prot, flags, fd, pgoff);
}
+
+#ifdef HAVE_ARCH_UNMAPPED_AREA
+/* solve cache aliasing problem (see Documentation/cache.txt and
+ arch/sparc64/kernel/sys_sparc.c */
+#define COLOUR_ALIGN(addr) (((addr)+SHMLBA-1)&~(SHMLBA-1))
+
+unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr, unsigned long len, unsigned long pgoff, unsigned long flags)
+{
+ struct vm_area_struct * vmm;
+
+ if (flags & MAP_FIXED) {
+ /* We do not accept a shared mapping if it would violate
+ * cache aliasing constraints.
+ */
+ if ((flags & MAP_SHARED) && (addr & (SHMLBA - 1)))
+ return -EINVAL;
+ return addr;
+ }
+
+ if (len > TASK_SIZE)
+ return -ENOMEM;
+ if (!addr)
+ addr = TASK_UNMAPPED_BASE;
+
+ if (flags & MAP_SHARED)
+ addr = COLOUR_ALIGN(addr);
+ else
+ addr = PAGE_ALIGN(addr);
+
+ for (vmm = find_vma(current->mm, addr); ; vmm = vmm->vm_next) {
+ /* At this point: (!vmm || addr < vmm->vm_end). */
+ if (TASK_SIZE - len < addr)
+ return -ENOMEM;
+ if (!vmm || addr + len <= vmm->vm_start)
+ return addr;
+ addr = vmm->vm_end;
+ if (flags & MAP_SHARED)
+ addr = COLOUR_ALIGN(addr);
+ }
+}
+#endif /* HAVE_ARCH_UNMAPPED_AREA */
save_static_function(sys_fork);
static_unused int _sys_fork(struct pt_regs regs)
diff -ur linux.sgi/include/asm-mips/pgtable.h linux/include/asm-mips/pgtable.h
--- linux.sgi/include/asm-mips/pgtable.h Sun Aug 5 23:41:28 2001
+++ linux/include/asm-mips/pgtable.h Mon Aug 6 16:17:11 2001
@@ -740,6 +740,9 @@
#include <asm-generic/pgtable.h>
+/* We provide our own get_unmapped_area to cope with VA holes for userland */
+#define HAVE_ARCH_UNMAPPED_AREA
+
#endif /* !defined (_LANGUAGE_ASSEMBLY) */
#define io_remap_page_range remap_page_range
