Re: [PATCH-for-6.1 v2] softmmu/physmem: fix wrong assertion in qemu_ram_alloc_internal()

[Peter Xu <peterx@redhat.com>]

On Thu, Aug 05, 2021 at 11:23:50AM +0200, David Hildenbrand wrote:
> When adding RAM_NORESERVE, we forgot to remove the old assertion when
> adding the updated one, most probably when reworking the patches or
> rebasing. We can easily crash QEMU by adding
>   -object memory-backend-ram,id=mem0,size=500G,reserve=off
> to the QEMU cmdline:
>   qemu-system-x86_64: ../softmmu/physmem.c:2146: qemu_ram_alloc_internal:
>   Assertion `(ram_flags & ~(RAM_SHARED | RAM_RESIZEABLE | RAM_PREALLOC))
>   == 0' failed.
> 
> Fix it by removing the old assertion.
> 
> Fixes: 8dbe22c6868b ("memory: Introduce RAM_NORESERVE and wire it up in qemu_ram_mmap()")
> Reviewed-by: Peter Xu <peterx@redhat.com>
> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Peter Xu <peterx@redhat.com>
> Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> 
> v1 -> v2:
> - Added rbs
> - Tagged for 6.1 inclusion
> 
> ---
>  softmmu/physmem.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/softmmu/physmem.c b/softmmu/physmem.c
> index 3c1912a1a0..2e18947598 100644
> --- a/softmmu/physmem.c
> +++ b/softmmu/physmem.c
> @@ -2143,7 +2143,6 @@ RAMBlock *qemu_ram_alloc_internal(ram_addr_t size, ram_addr_t max_size,
>      RAMBlock *new_block;
>      Error *local_err = NULL;
>  
> -    assert((ram_flags & ~(RAM_SHARED | RAM_RESIZEABLE | RAM_PREALLOC)) == 0);
>      assert((ram_flags & ~(RAM_SHARED | RAM_RESIZEABLE | RAM_PREALLOC |
>                            RAM_NORESERVE)) == 0);
>      assert(!host ^ (ram_flags & RAM_PREALLOC));
> -- 
> 2.31.1
> 

Today I just noticed this patch is still missing for 6.1. How many users are
there with reserve=off?  Would it be worth rc4 or not?

-- 
Peter Xu