[Qemu-devel] [PATCH v3] linux-user: fix mmap_find_vma_reserved()

[Qemu-devel] [PATCH v3] linux-user: fix mmap_find_vma_reserved()

[Laurent Vivier]

The value given by mmap_find_vma_reserved() is used with mmap(),
so it is needed to be aligned with the host page size.

Since commit 18e80c55bb, reserved_va is only aligned to TARGET_PAGE_SIZE,
and it works well if this size is greater or equal to the host page size.

But ppc64 hosts have 64kB page size and when we start a 4kiB page size
guest (like i386), it fails when it tries to mmap the stack:

    mmap stack: Invalid argument

Fixes: 18e80c55bb (linux-user: Tidy and enforce reserved_va initialization)
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
---

Notes:
    v3:
      move initialization of reserved_va to main()
    
    v2:
      fix typo s/has/as/

 linux-user/main.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/linux-user/main.c b/linux-user/main.c
index 52b5a618fe..ea00dd9057 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -78,14 +78,7 @@ int have_guest_base;
 # endif
 #endif
 
-/* That said, reserving *too* much vm space via mmap can run into problems
-   with rlimits, oom due to page table creation, etc.  We will still try it,
-   if directed by the command-line option, but not by default.  */
-#if HOST_LONG_BITS == 64 && TARGET_VIRT_ADDR_SPACE_BITS <= 32
-unsigned long reserved_va = MAX_RESERVED_VA;
-#else
 unsigned long reserved_va;
-#endif
 
 static void usage(int exitcode);
 
@@ -672,6 +665,18 @@ int main(int argc, char **argv, char **envp)
     /* init tcg before creating CPUs and to get qemu_host_page_size */
     tcg_exec_init(0);
 
+    /* Reserving *too* much vm space via mmap can run into problems
+       with rlimits, oom due to page table creation, etc.  We will still try it,
+       if directed by the command-line option, but not by default.  */
+    if (HOST_LONG_BITS == 64 &&
+        TARGET_VIRT_ADDR_SPACE_BITS <= 32 &&
+        reserved_va == 0) {
+        /* reserved_va must be aligned with the host page size
+         * as it is used with mmap()
+         */
+        reserved_va = MAX_RESERVED_VA & qemu_host_page_mask;
+    }
+
     cpu = cpu_create(cpu_type);
     env = cpu->env_ptr;
     cpu_reset(cpu);
-- 
2.17.1

Re: [Qemu-devel] [PATCH v3] linux-user: fix mmap_find_vma_reserved()

[Richard Henderson]

On 07/14/2018 02:35 PM, Laurent Vivier wrote:
> The value given by mmap_find_vma_reserved() is used with mmap(),
> so it is needed to be aligned with the host page size.
> 
> Since commit 18e80c55bb, reserved_va is only aligned to TARGET_PAGE_SIZE,
> and it works well if this size is greater or equal to the host page size.
> 
> But ppc64 hosts have 64kB page size and when we start a 4kiB page size
> guest (like i386), it fails when it tries to mmap the stack:
> 
>     mmap stack: Invalid argument
> 
> Fixes: 18e80c55bb (linux-user: Tidy and enforce reserved_va initialization)
> Signed-off-by: Laurent Vivier <laurent@vivier.eu>
> ---
> 
> Notes:
>     v3:
>       move initialization of reserved_va to main()
>     
>     v2:
>       fix typo s/has/as/
> 
>  linux-user/main.c | 19 ++++++++++++-------
>  1 file changed, 12 insertions(+), 7 deletions(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~