Re: [Qemu-devel] [PATCH] hw/virtio/balloon: Replace TARGET_PAGE_SIZE with BALLOON_PAGE_SIZE

[David Gibson <dgibson@redhat.com>]

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On Thu, 14 Apr 2016 10:50:07 +0200
Thomas Huth <thuth@redhat.com> wrote:

> The balloon code currently calls madvise() with TARGET_PAGE_SIZE as
> length parameter. Since the virtio-balloon protocol is always based
> on 4k pages, no matter what the host and guest are using as page size,
> this could cause problems: If TARGET_PAGE_SIZE is bigger than 4k, the
> madvise call also destroys the 4k areas after the current one - which
> might be wrong since the guest did not want free that area yet (in
> case the guest used as smaller MMU page size than the hard-coded
> TARGET_PAGE_SIZE). So to fix this issue, introduce a proper define
> called BALLOON_PAGE_SIZE (which is 4096) to use this as the size
> parameter for the madvise() call instead.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>

Reviewed-by: David Gibson <dgibson@redhat.com>

> ---
>  hw/virtio/virtio-balloon.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index c74101e..9dbe681 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -19,7 +19,6 @@
>  #include "qemu-common.h"
>  #include "hw/virtio/virtio.h"
>  #include "hw/i386/pc.h"
> -#include "cpu.h"
>  #include "sysemu/balloon.h"
>  #include "hw/virtio/virtio-balloon.h"
>  #include "sysemu/kvm.h"
> @@ -35,12 +34,14 @@
>  #include "hw/virtio/virtio-bus.h"
>  #include "hw/virtio/virtio-access.h"
>  
> +#define BALLOON_PAGE_SIZE  (1 << VIRTIO_BALLOON_PFN_SHIFT)
> +
>  static void balloon_page(void *addr, int deflate)
>  {
>  #if defined(__linux__)
>      if (!qemu_balloon_is_inhibited() && (!kvm_enabled() ||
>                                           kvm_has_sync_mmu())) {
> -        qemu_madvise(addr, TARGET_PAGE_SIZE,
> +        qemu_madvise(addr, BALLOON_PAGE_SIZE,
>                  deflate ? QEMU_MADV_WILLNEED : QEMU_MADV_DONTNEED);
>      }
>  #endif
> -- 
> 1.8.3.1
> 


-- 
David Gibson <dgibson@redhat.com>
Senior Software Engineer, Virtualization, Red Hat

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