Re: [Qemu-devel] [PATCH] extend limit of physical sections number

[Amos Kong]

On Sat, Sep 28, 2013 at 12:49:20AM +0800, Amos Kong wrote:
>  # qemu -drive file=/disk0,if=none,id=v0,format=qcow2 \
>  -device virtio-blk-pci,drive=v0,id=v00,multifunction=on,addr=0x04.0
>  ....
> 
> Launching guest with more than 32 virtio-blk disks,
> qemu will crash, because there are too many BARs.
> 
> This patch brings the limit of non-tcg up by a factor
> of 8 (32767 / 4096), i.e. 32*8 = 256.

I re-tested with latest guest kernel (3.10.0-rc5),
crash still occurred after applied this patch.


1. phys_section_add: assert(next_map.sections_nb < TARGET_PAGE_SIZE);
   crash

2. phys_section_add: assert(next_map.sections_nb < SHRT_MAX);
   crash

3. without this assert of next_map.sections_nb in phys_section_add
   crash occurred at register_subpage():
   assert(existing->mr->subpage || existing->mr == &io_mem_unassigned);

 
> Signed-off-by: Paolo Bonzini <address@hidden>
> Signed-off-by: Amos Kong <address@hidden>
> ---
>  exec.c | 17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index 5aef833..f639c01 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -763,11 +763,18 @@ void phys_mem_set_alloc(void *(*alloc)(ram_addr_t))
>  
>  static uint16_t phys_section_add(MemoryRegionSection *section)
>  {
> -    /* The physical section number is ORed with a page-aligned
> -     * pointer to produce the iotlb entries.  Thus it should
> -     * never overflow into the page-aligned value.
> -     */
> -    assert(next_map.sections_nb < TARGET_PAGE_SIZE);
> +    if (tcg_enabled()) {
> +        /* The physical section number is ORed with a page-aligned
> +         * pointer to produce the iotlb entries.  Thus it should
> +         * never overflow into the page-aligned value.
> +         */
> +        assert(next_map.sections_nb < TARGET_PAGE_SIZE);
> +    } else {
> +        /* For KVM or Xen we can use the full range of the ptr field
> +         * in PhysPageEntry.
> +         */
> +        assert(next_map.sections_nb < SHRT_MAX);
> +    }
>  
>      if (next_map.sections_nb == next_map.sections_nb_alloc) {
>          next_map.sections_nb_alloc = MAX(next_map.sections_nb_alloc * 2,
> -- 
> 1.8.3.1
> 

-- 
                        Amos.