Re: [Qemu-devel] [PATCH] migration: ensure memory is zeroized at the destination

[Peter Lieven <pl@kamp.de>]

please ignore this one.

Peter

On 10.06.2013 09:03, Peter Lieven wrote:
> migration relies on the target memory to be zeroed out since commit
> f1c72795 (migration: do not sent zero pages in bulk stage). however,
> there is a subtle case where this breaks migration. if for some reason
> a page is zero at the source but not at the destination the destination
> memory is corrupted.
>
> this was reported to break migration on pseries and also other platforms
> might be affected. to ultimatively make sure the destination memory is zero
> at the destination check for it on negotiation of ram blocks.
>
> note: the better fix for this would be to pass a flag to the machine
> init functions of all architectures to indicate that the machine is a
> migration target and then avoid copying ram images etc. to physical
> ram in this case. but this would require a lot of code to be changed
> and reviewed.
>
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
>   arch_init.c |   10 ++++++++++
>   1 file changed, 10 insertions(+)
>
> diff --git a/arch_init.c b/arch_init.c
> index 5d32ecf..458bf8c 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -799,6 +799,8 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
>                   while (total_ram_bytes) {
>                       RAMBlock *block;
>                       uint8_t len;
> +                    void *base;
> +                    ram_addr_t offset;
>   
>                       len = qemu_get_byte(f);
>                       qemu_get_buffer(f, (uint8_t *)id, len);
> @@ -822,6 +824,14 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
>                           goto done;
>                       }
>   
> +                    base = memory_region_get_ram_ptr(block->mr);
> +                    for (offset = 0; offset < block->length;
> +                         offset += TARGET_PAGE_SIZE) {
> +                        if (!is_zero_page(base + offset)) {
> +                            memset(base + offset, 0x00, TARGET_PAGE_SIZE);
> +                        }
> +                    }
> +
>                       total_ram_bytes -= length;
>                   }
>               }


-- 

Mit freundlichen Grüßen

Peter Lieven

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