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Re: [Xen-devel] [PATCH v2] xen-mapcache: use MAP_FIXED flag so the mmap address hint is always honored
- To: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Mon, 18 Mar 2019 17:03:55 +0100
- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Eduardo Habkost <ehabkost@xxxxxxxxxx>, "Michael S. Tsirkin" <mst@xxxxxxxxxx>, qemu-devel@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 16:06:00 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Mon, Mar 18, 2019 at 03:48:59PM +0000, Igor Druzhinin wrote:
> 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?
I felt that was too far from the actual call, but I can move it if
there's consensus.
Thanks, Roger.
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