[Qemu-devel] [PATCH v3] 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 Reviewed-by: Paul Durrant --- Cc: Stefano Stabellini Cc: Anthony Perard Cc: Paul Durrant Cc: Igor Druzhinin Cc: Paolo Bonzini Cc: Richard Henderson Cc: Eduardo Habkost Cc: "Michael S. Tsirkin" Cc: Marcel Apfelbaum Cc: xen-de...@lists.xenproject.org --- Changes since v2: - Move comment position. 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..254759f776 100644 --- a/hw/i386/xen/xen-mapcache.c +++ b/hw/i386/xen/xen-mapcache.c @@ -184,9 +184,14 @@ static void xen_remap_bucket(MapCacheEntry *entry, pfns[i] = (address_index << (MCACHE_BUCKET_SHIFT-XC_PAGE_SHIFT)) + i; } +/* + * If the caller has requested the mapping at a specific address use + * MAP_FIXED to make sure it's honored. + */ if (!dummy) { 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); if (vaddr_base == NULL) { perror("xenforeignmemory_map2"); @@ -198,7 +203,8 @@ static void xen_remap_bucket(MapCacheEntry *entry, * mapping immediately due to certain circumstances (i.e. on resume now) */ vaddr_base = mmap(vaddr, size, PROT_READ | PROT_WRITE, - MAP_ANON | MAP_SHARED, -1, 0); + MAP_ANON | MAP_SHARED | (vaddr ? MAP_FIXED : 0), + -1, 0); if (vaddr_base == MAP_FAILED) { perror("mmap"); exit(-1); -- 2.17.2 (Apple Git-113)
Re: [Qemu-devel] [PATCH v3] xen-mapcache: use MAP_FIXED flag so the mmap address hint is always honored
On 18/03/2019 17:37, 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 > Reviewed-by: Paul Durrant > --- > Cc: Stefano Stabellini > Cc: Anthony Perard > Cc: Paul Durrant > Cc: Igor Druzhinin > Cc: Paolo Bonzini > Cc: Richard Henderson > Cc: Eduardo Habkost > Cc: "Michael S. Tsirkin" > Cc: Marcel Apfelbaum > Cc: xen-de...@lists.xenproject.org > --- > Changes since v2: > - Move comment position. > > 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..254759f776 100644 > --- a/hw/i386/xen/xen-mapcache.c > +++ b/hw/i386/xen/xen-mapcache.c > @@ -184,9 +184,14 @@ static void xen_remap_bucket(MapCacheEntry *entry, > pfns[i] = (address_index << (MCACHE_BUCKET_SHIFT-XC_PAGE_SHIFT)) + i; > } > > +/* > + * If the caller has requested the mapping at a specific address use > + * MAP_FIXED to make sure it's honored. > + */ > if (!dummy) { > 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); > if (vaddr_base == NULL) { > perror("xenforeignmemory_map2"); > @@ -198,7 +203,8 @@ static void xen_remap_bucket(MapCacheEntry *entry, > * mapping immediately due to certain circumstances (i.e. on resume > now) > */ > vaddr_base = mmap(vaddr, size, PROT_READ | PROT_WRITE, > - MAP_ANON | MAP_SHARED, -1, 0); > + MAP_ANON | MAP_SHARED | (vaddr ? MAP_FIXED : 0), > + -1, 0); > if (vaddr_base == MAP_FAILED) { > perror("mmap"); > exit(-1); > Reviewed-by: Igor Druzhinin Igor
Re: [Qemu-devel] [PATCH v3] xen-mapcache: use MAP_FIXED flag so the mmap address hint is always honored
On Mon, Mar 18, 2019 at 06:37:31PM +0100, 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 > Reviewed-by: Paul Durrant Acked-by: Anthony PERARD -- Anthony PERARD