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Re: [Xen-devel] [PATCH v2] xen-mapcache: use MAP_FIXED flag so the mmap address hint is always honored
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>, <qemu-devel@xxxxxxxxxx>
- From: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
- Date: Mon, 18 Mar 2019 15:48:59 +0000
- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Eduardo Habkost <ehabkost@xxxxxxxxxx>, "Michael S. Tsirkin" <mst@xxxxxxxxxx>, Paul Durrant <paul.durrant@xxxxxxxxxx>, Marcel Apfelbaum <marcel.apfelbaum@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Anthony Perard <anthony.perard@xxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Richard Henderson <rth@xxxxxxxxxxx>
- Delivery-date: Mon, 18 Mar 2019 15:49:12 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 18/03/2019 15:45, Roger Pau Monne wrote:
> Or if it's not possible to honor the hinted address an error is returned
> instead. This makes it easier to spot the actual failure, instead of
> failing later on when the caller of xen_remap_bucket realizes the
> mapping has not been created at the requested address.
>
> Also note that at least on FreeBSD using MAP_FIXED will cause mmap to
> try harder to honor the passed address.
>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Anthony Perard <anthony.perard@xxxxxxxxxx>
> Cc: Paul Durrant <paul.durrant@xxxxxxxxxx>
> Cc: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Richard Henderson <rth@xxxxxxxxxxx>
> Cc: Eduardo Habkost <ehabkost@xxxxxxxxxx>
> Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
> Cc: Marcel Apfelbaum <marcel.apfelbaum@xxxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
> ---
> Changes since v1:
> - Use MAP_FIXED for the dummy mmap call also if a specific virtual
> address is requested.
> ---
> hw/i386/xen/xen-mapcache.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/hw/i386/xen/xen-mapcache.c b/hw/i386/xen/xen-mapcache.c
> index 349f72d00c..23de5517db 100644
> --- a/hw/i386/xen/xen-mapcache.c
> +++ b/hw/i386/xen/xen-mapcache.c
> @@ -185,8 +185,13 @@ static void xen_remap_bucket(MapCacheEntry *entry,
> }
>
> if (!dummy) {
> + /*
> + * If the caller has requested the mapping at a specific address use
> + * MAP_FIXED to make sure it's honored.
> + */
Since the comment now applied to both invocation - could it be moved
outside the if statement then?
Igor
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