Merge tag 'mips_fixes_4.19_1' of git://git.kernel.org/pub/scm/linux/kernel/git/mips/linux

Pull MIPS fix from Paul Burton:
 "A single fix for v4.19-rc3, resolving a problem with our VDSO data
  page for systems with dcache aliasing. Those systems could previously
  observe stale data, causing clock_gettime() & gettimeofday() to return
  incorrect values"

* tag 'mips_fixes_4.19_1' of git://git.kernel.org/pub/scm/linux/kernel/git/mips/linux:
  MIPS: VDSO: Match data page cache colouring when D$ aliases

1 files changed, 20 insertions, 0 deletions

diff --git a/arch/mips/kernel/vdso.c b/arch/mips/kernel/vdso.c
index 019035d7225c..8f845f6e5f42 100644
--- a/arch/mips/kernel/vdso.c
+++ b/arch/mips/kernel/vdso.c
@@ -13,6 +13,7 @@
 #include <linux/err.h>
 #include <linux/init.h>
 #include <linux/ioport.h>
+#include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
@@ -20,6 +21,7 @@
 
 #include <asm/abi.h>
 #include <asm/mips-cps.h>
+#include <asm/page.h>
 #include <asm/vdso.h>
 
 /* Kernel-provided data used by the VDSO. */
@@ -128,12 +130,30 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
         vvar_size = gic_size + PAGE_SIZE;
         size = vvar_size + image->size;
 
+        /*
+         * Find a region that's large enough for us to perform the
+         * colour-matching alignment below.
+         */
+        if (cpu_has_dc_aliases)
+                size += shm_align_mask + 1;
+
         base = get_unmapped_area(NULL, 0, size, 0, 0);
         if (IS_ERR_VALUE(base)) {
                 ret = base;
                 goto out;
         }
 
+        /*
+         * If we suffer from dcache aliasing, ensure that the VDSO data page
+         * mapping is coloured the same as the kernel's mapping of that memory.
+         * This ensures that when the kernel updates the VDSO data userland
+         * will observe it without requiring cache invalidations.
+         */
+        if (cpu_has_dc_aliases) {
+                base = __ALIGN_MASK(base, shm_align_mask);
+                base += ((unsigned long)&vdso_data - gic_size) & shm_align_mask;
+        }
+
         data_addr = base + gic_size;
         vdso_addr = data_addr + PAGE_SIZE;