riscv/vdso: Move vdso data page up front

As commit 601255ae3c98 ("arm64: vdso: move data page before code pages"), the
same issue exists on riscv, testcase is shown below, make sure that vdso.so is
bigger than page size,

  struct timespec tp;
  clock_gettime(5, &tp);
  printf("tv_sec: %ld, tv_nsec: %ld\n", tp.tv_sec, tp.tv_nsec);

without this patch, test result : tv_sec: 0, tv_nsec: 0
   with this patch, test result : tv_sec: 1629271537, tv_nsec: 748000000

Move the vdso data page in front of the VDSO area to fix the issue.

Fixes: ad5d1122b82fb ("riscv: use vDSO common flow to reduce the latency of the time-related functions")
Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

diff --git a/arch/riscv/include/asm/vdso.h b/arch/riscv/include/asm/vdso.h
index a4a979c..208e31b 100644 (file)
--- a/arch/riscv/include/asm/vdso.h
+++ b/arch/riscv/include/asm/vdso.h
@@ -22,6 +22,8 @@
  */
 #ifdef CONFIG_MMU
 
+#define __VVAR_PAGES    1
+
 #ifndef __ASSEMBLY__
 #include <generated/vdso-offsets.h>
 

diff --git a/arch/riscv/kernel/vdso.c b/arch/riscv/kernel/vdso.c
index 72e93d2..e7bd92d 100644 (file)
--- a/arch/riscv/kernel/vdso.c
+++ b/arch/riscv/kernel/vdso.c
@@ -23,6 +23,13 @@ struct vdso_data {
 
 extern char vdso_start[], vdso_end[];
 
+enum vvar_pages {
+       VVAR_DATA_PAGE_OFFSET,
+       VVAR_NR_PAGES,
+};
+
+#define VVAR_SIZE  (VVAR_NR_PAGES << PAGE_SHIFT)
+
 static unsigned int vdso_pages __ro_after_init;
 static struct page **vdso_pagelist __ro_after_init;
 
@@ -41,7 +48,7 @@ static int __init vdso_init(void)
 
        vdso_pages = (vdso_end - vdso_start) >> PAGE_SHIFT;
        vdso_pagelist =
-               kcalloc(vdso_pages + 1, sizeof(struct page *), GFP_KERNEL);
+               kcalloc(vdso_pages + VVAR_NR_PAGES, sizeof(struct page *), GFP_KERNEL);
        if (unlikely(vdso_pagelist == NULL)) {
                pr_err("vdso: pagelist allocation failed\n");
                return -ENOMEM;
@@ -66,7 +73,9 @@ int arch_setup_additional_pages(struct linux_binprm *bprm,
        unsigned long vdso_base, vdso_len;
        int ret;
 
-       vdso_len = (vdso_pages + 1) << PAGE_SHIFT;
+       BUILD_BUG_ON(VVAR_NR_PAGES != __VVAR_PAGES);
+
+       vdso_len = (vdso_pages + VVAR_NR_PAGES) << PAGE_SHIFT;
 
        mmap_write_lock(mm);
        vdso_base = get_unmapped_area(NULL, 0, vdso_len, 0, 0);
@@ -75,29 +84,28 @@ int arch_setup_additional_pages(struct linux_binprm *bprm,
                goto end;
        }
 
-       /*
-        * Put vDSO base into mm struct. We need to do this before calling
-        * install_special_mapping or the perf counter mmap tracking code
-        * will fail to recognise it as a vDSO (since arch_vma_name fails).
-        */
-       mm->context.vdso = (void *)vdso_base;
+       mm->context.vdso = NULL;
+       ret = install_special_mapping(mm, vdso_base, VVAR_SIZE,
+               (VM_READ | VM_MAYREAD), &vdso_pagelist[vdso_pages]);
+       if (unlikely(ret))
+               goto end;
 
        ret =
-          install_special_mapping(mm, vdso_base, vdso_pages << PAGE_SHIFT,
+          install_special_mapping(mm, vdso_base + VVAR_SIZE,
+               vdso_pages << PAGE_SHIFT,
                (VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC),
                vdso_pagelist);
 
-       if (unlikely(ret)) {
-               mm->context.vdso = NULL;
+       if (unlikely(ret))
                goto end;
-       }
 
-       vdso_base += (vdso_pages << PAGE_SHIFT);
-       ret = install_special_mapping(mm, vdso_base, PAGE_SIZE,
-               (VM_READ | VM_MAYREAD), &vdso_pagelist[vdso_pages]);
+       /*
+        * Put vDSO base into mm struct. We need to do this before calling
+        * install_special_mapping or the perf counter mmap tracking code
+        * will fail to recognise it as a vDSO (since arch_vma_name fails).
+        */
+       mm->context.vdso = (void *)vdso_base + VVAR_SIZE;
 
-       if (unlikely(ret))
-               mm->context.vdso = NULL;
 end:
        mmap_write_unlock(mm);
        return ret;
@@ -108,7 +116,7 @@ const char *arch_vma_name(struct vm_area_struct *vma)
        if (vma->vm_mm && (vma->vm_start == (long)vma->vm_mm->context.vdso))
                return "[vdso]";
        if (vma->vm_mm && (vma->vm_start ==
-                          (long)vma->vm_mm->context.vdso + PAGE_SIZE))
+                          (long)vma->vm_mm->context.vdso - VVAR_SIZE))
                return "[vdso_data]";
        return NULL;
 }

diff --git a/arch/riscv/kernel/vdso/vdso.lds.S b/arch/riscv/kernel/vdso/vdso.lds.S
index e6f558b..e9111f7 100644 (file)
--- a/arch/riscv/kernel/vdso/vdso.lds.S
+++ b/arch/riscv/kernel/vdso/vdso.lds.S
@@ -3,12 +3,13 @@
  * Copyright (C) 2012 Regents of the University of California
  */
 #include <asm/page.h>
+#include <asm/vdso.h>
 
 OUTPUT_ARCH(riscv)
 
 SECTIONS
 {
-       PROVIDE(_vdso_data = . + PAGE_SIZE);
+       PROVIDE(_vdso_data = . - __VVAR_PAGES * PAGE_SIZE);
        . = SIZEOF_HEADERS;
 
        .hash           : { *(.hash) }                  :text