Re: [Qemu-devel] Re: [Qemu-commits] [COMMIT 3086844] Instead of writing a zero page, madvise it away

[Avi Kivity <avi@redhat.com>]

On 06/22/2009 08:44 PM, Anthony Liguori wrote:
> See attached.
> Author: Anthony Liguori<aliguori@us.ibm.com>
> Date:   Mon Jun 22 12:39:00 2009 -0500
>
>      Make sure to zero out memory before calling madvise to increase robustness
>
>      Avi pointed out that it's not entirely safe to rely on madvise zeroing out
>      memory.  So let's do it explicitly before calling madvise.
>
>      Signed-off-by: Anthony Liguori<aliguori@us.ibm.com>
>
> diff --git a/vl.c b/vl.c
> index 60a00e1..1c077b4 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -3358,13 +3358,13 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
>
>           if (flags&  RAM_SAVE_FLAG_COMPRESS) {
>               uint8_t ch = qemu_get_byte(f);
> -#if defined(__linux__)
> +            memset(qemu_get_ram_ptr(addr), ch, TARGET_PAGE_SIZE);
> +#ifndef _WIN32
>               if (ch == 0&&
>                   (!kvm_enabled() || kvm_has_sync_mmu())) {
>                   madvise(qemu_get_ram_ptr(addr), TARGET_PAGE_SIZE, MADV_DONTNEED);
> -            } else
> +            }
>   #endif
> -            memset(qemu_get_ram_ptr(addr), ch, TARGET_PAGE_SIZE);
>           } else if (flags&  RAM_SAVE_FLAG_PAGE)
>               qemu_get_buffer(f, qemu_get_ram_ptr(addr), TARGET_PAGE_SIZE);
>       } while (!(flags&  RAM_SAVE_FLAG_EOS));
>    

Pretty similar to my December patch... which had another case, is it 
missing?

http://article.gmane.org/gmane.comp.emulators.qemu/34523

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.