Re: [PATCH for-8.0 11/11] linux-user/arm: Take more care allocating commpage

["Alex Bennée" <alex.bennee@linaro.org>]

Richard Henderson <richard.henderson@linaro.org> writes:

> User setting of -R reserved_va can lead to an assertion
> failure in page_set_flags.  Sanity check the value of
> reserved_va and print an error message instead.  Do not
> allocate a commpage at all for m-profile cpus.

I see this:

  TEST    convd on i386
qemu-i386: Unable to reserve 0x100000000 bytes of virtual address space
at 0x8000 (File exists) for use as guest address space (check your
virtual memory ulimit setting, min_mmap_addr or reserve less using -R
option)

on the ubuntu aarch64 static build:

  https://gitlab.com/stsquad/qemu/-/jobs/4003523064

>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  linux-user/elfload.c | 37 +++++++++++++++++++++++++++----------
>  1 file changed, 27 insertions(+), 10 deletions(-)
>
> diff --git a/linux-user/elfload.c b/linux-user/elfload.c
> index b068676340..0529430b1d 100644
> --- a/linux-user/elfload.c
> +++ b/linux-user/elfload.c
> @@ -422,12 +422,32 @@ enum {
>  
>  static bool init_guest_commpage(void)
>  {
> -    abi_ptr commpage = HI_COMMPAGE & -qemu_host_page_size;
> -    void *want = g2h_untagged(commpage);
> -    void *addr = mmap(want, qemu_host_page_size, PROT_READ | PROT_WRITE,
> -                      MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1, 0);
> +    ARMCPU *cpu = ARM_CPU(thread_cpu);
> +    abi_ptr want = HI_COMMPAGE & TARGET_PAGE_MASK;
> +    abi_ptr addr;
>  
> -    if (addr == MAP_FAILED) {
> +    /*
> +     * M-profile allocates maximum of 2GB address space, so can never
> +     * allocate the commpage.  Skip it.
> +     */
> +    if (arm_feature(&cpu->env, ARM_FEATURE_M)) {
> +        return true;
> +    }
> +
> +    /*
> +     * If reserved_va does not cover the commpage, we get an assert
> +     * in page_set_flags.  Produce an intelligent error instead.
> +     */
> +    if (reserved_va != 0 && want + TARGET_PAGE_SIZE - 1 > reserved_va) {
> +        error_report("Allocating guest commpage: -R 0x%" PRIx64 " too small",
> +                     (uint64_t)reserved_va + 1);
> +        exit(EXIT_FAILURE);
> +    }
> +
> +    addr = target_mmap(want, TARGET_PAGE_SIZE, PROT_READ | PROT_WRITE,
> +                       MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1, 0);
> +
> +    if (addr == -1) {
>          perror("Allocating guest commpage");
>          exit(EXIT_FAILURE);
>      }
> @@ -436,15 +456,12 @@ static bool init_guest_commpage(void)
>      }
>  
>      /* Set kernel helper versions; rest of page is 0.  */
> -    __put_user(5, (uint32_t *)g2h_untagged(0xffff0ffcu));
> +    put_user_u32(5, 0xffff0ffcu);
>  
> -    if (mprotect(addr, qemu_host_page_size, PROT_READ)) {
> +    if (target_mprotect(addr, qemu_host_page_size, PROT_READ | PROT_EXEC)) {
>          perror("Protecting guest commpage");
>          exit(EXIT_FAILURE);
>      }
> -
> -    page_set_flags(commpage, commpage | ~qemu_host_page_mask,
> -                   PAGE_READ | PAGE_EXEC | PAGE_VALID);
>      return true;
>  }


-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro