> -----Original Message-----
> From: Roger Pau Monne [mailto:roger....@citrix.com]
> Sent: 15 March 2019 08:59
> To: qemu-devel@nongnu.org
> Cc: Roger Pau Monne <roger....@citrix.com>; Stefano Stabellini
> <sstabell...@kernel.org>; Anthony
> Perard <anthony.per...@citrix.com>; Paul Durrant <paul.durr...@citrix.com>;
> Igor Druzhinin
> <igor.druzhi...@citrix.com>; Paolo Bonzini <pbonz...@redhat.com>; Richard
> Henderson <r...@twiddle.net>;
> Eduardo Habkost <ehabk...@redhat.com>; Michael S. Tsirkin <m...@redhat.com>;
> Marcel Apfelbaum
> <marcel.apfelb...@gmail.com>; xen-de...@lists.xenproject.org
> Subject: [PATCH] xen-mapcache: use MAP_FIXED flag so the mmap address hint is
> always honored
>
> 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....@citrix.com>
> ---
> Cc: Stefano Stabellini <sstabell...@kernel.org>
> Cc: Anthony Perard <anthony.per...@citrix.com>
> Cc: Paul Durrant <paul.durr...@citrix.com>
> Cc: Igor Druzhinin <igor.druzhi...@citrix.com>
> Cc: Paolo Bonzini <pbonz...@redhat.com>
> Cc: Richard Henderson <r...@twiddle.net>
> Cc: Eduardo Habkost <ehabk...@redhat.com>
> Cc: "Michael S. Tsirkin" <m...@redhat.com>
> Cc: Marcel Apfelbaum <marcel.apfelb...@gmail.com>
> Cc: xen-de...@lists.xenproject.org
> ---
> hw/i386/xen/xen-mapcache.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/hw/i386/xen/xen-mapcache.c b/hw/i386/xen/xen-mapcache.c
> index 349f72d00c..0e2870b320 100644
> --- a/hw/i386/xen/xen-mapcache.c
> +++ b/hw/i386/xen/xen-mapcache.c
> @@ -185,8 +185,14 @@ 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. Note that with MAP_FIXED at
> + * least FreeBSD will try harder to honor the passed address.
> + */
> vaddr_base = xenforeignmemory_map2(xen_fmem, xen_domid, vaddr,
> - PROT_READ | PROT_WRITE, 0,
> + PROT_READ | PROT_WRITE,
> + vaddr ? MAP_FIXED : 0,
> nb_pfn, pfns, err);
AFAICT xen_remap_bucket() is always called with a NULL vaddr argument if
entry->vaddr_base == NULL, and called with vaddr == entry->vaddr_base in the
other case, so I'd say the vaddr argument is superfluous.
So, I think it would be better to just use entry->vaddr_base in the call above
and I also wonder whether the mmap() below should only be allowed to happen if
entry->vaddr_base == NULL.
Paul
> if (vaddr_base == NULL) {
> perror("xenforeignmemory_map2");
> --
> 2.17.2 (Apple Git-113)
