Re: [Qemu-devel] [PATCH] exec.c: workaround regression caused by alignment change in d2f39ad

[Paolo Bonzini <pbonzini@redhat.com>]

On 24/10/2016 14:49, Haozhong Zhang wrote:
> Commit d2f39ad "exec.c: Ensure right alignment also for file backed ram"
> added an additional alignment requirement on the size of backend file
> besides the previous page size. On x86, the alignment is changed from
> 4KB in QEMU 2.6 to 2MB in QEMU 2.7.
> 
> This change breaks certain usages in QEMU 2.7 on x86, e.g.
>     -object memory-backend-file,id=mem1,mem-path=/tmp/,size=$SZ
>     -device pc-dimm,id=dimm1,memdev=mem1
> where $SZ is multiple of 4KB but not 2MB (e.g. 1023M). QEMU 2.7
> reports the following error message and aborts:
> qemu-system-x86_64: -device pc-dimm,memdev=mem1,id=nv1: backend memory size must be multiple of 0x200000
> 
> The same regression may also happen in other platforms as indicated by
> Igor Mammedov. This change is however necessary for s390 according to
> the commit message of d2f39ad, so we workaround the regression by taking
> the change only on s390.
> 
> Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
> Reported-by: "Xu, Anthony" <anthony.xu@intel.com>
> ---
>  exec.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/exec.c b/exec.c
> index e63c5a1..55915ea 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -1254,7 +1254,11 @@ static void *file_ram_alloc(RAMBlock *block,
>      }
>  
>      block->page_size = qemu_fd_getpagesize(fd);
> +#if defined(__s390x__)
>      block->mr->align = MAX(block->page_size, QEMU_VMALLOC_ALIGN);
> +#else
> +    block->mr->align = block->page_size;
> +#endif

Better:

	block->mr->align = block->page_size;
#ifdef __s390x__
	if (kvm_enabled()) {
	    block->mr->align = MAX(block->mr->align, QEMU_VMALLOC_ALIGN);
	}
#endif

Queued with this change.

Paolo

>  
>      if (memory < block->page_size) {
>          error_setg(errp, "memory size 0x" RAM_ADDR_FMT " must be equal to "
>