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References: <20161021082801.dglwfsocljohquok@hz-desktop>
From: Haozhong Zhang <haozhong.zhang@intel.com>
Message-ID: <695474a1-1a40-8b1d-42bb-013e7d4119a4@intel.com>
Date: Fri, 21 Oct 2016 16:39:08 +0800
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Subject: Re: [Qemu-devel] Regression caused by d2f39ad "exec.c: Ensure right
 alignment also for file backed ram"
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To: qemu-devel@nongnu.org
Cc: chao.p.peng@intel.com, Eduardo Habkost <ehabkost@redhat.com>, Peter Crosthwaite <crosthwaite.peter@gmail.com>, Dominik Dingel <dingel@linux.vnet.ibm.com>, anthony.xu@intel.com, Igor Mammedov <imammedo@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Richard Henderson <rth@twiddle.net>, Xiao Guangrong <guangrong.xiao@linux.intel.com>

On 10/21/2016 04:28 PM, Haozhong Zhang wrote:
> Hi,
>
> Commit d2f39ad "exec.c: Ensure right alignment also for file backed
> ram" added an additional alignment requirement besides to the previous
> page size for the size of the backend file. On x86, the alignment
> requirement for the size of the backend file is changed from 4KB in
> QEMU 2.6 to 2MB in QEMU 2.7.
>
> This change immediately breaks the usage of "-object
> memory-backend-file,...,size=$SIZE"

I forgot the frontend part, the broken usage should be
    -object memory-backend-file,id=mem1,mem-path=$FILE,size=$SIZE
    -device nvdimm,id=nv1,memdev=mem1
where $SIZE is multiple of 4KB but not 2MB.

It works on QEMU 2.6, but fails on 2.7 when pc_dimm_memory_plug() tries
to plug the nvdimm device.

Haozhong

> on x86, where $SIZE is multiple of 4KB but not 2MB. It works on QEMU 2.6.
> Could this be considered as a regression?
>
> The commit message shows it's for s390. I'm wondering whether the same
> regression happens on s390 and ARM. If not, could I fix the regression
> on x86 by keeping using the original alignment only on x86, e.g.
>
> modified   exec.c
> @@ -1254,7 +1254,11 @@ static void *file_ram_alloc(RAMBlock *block,
>     }
>
>     block->page_size = qemu_fd_getpagesize(fd);
> +#if defined(__x86_64__) || defined(__i386__)
> +    block->mr->align = block->page_size;
> +#else
>     block->mr->align = MAX(block->page_size, QEMU_VMALLOC_ALIGN);
> +#endif
>
>     if (memory < block->page_size) {
>         error_setg(errp, "memory size 0x" RAM_ADDR_FMT " must be equal
> to "
>
>
> Thanks,
> Haozhong
>