Re: [Xen-devel] [PATCH QEMU-XEN v3 3/8] xen: Switch uses of xc_map_foreign_range into xc_map_foreign_bulk

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 7 Oct 2015, Ian Campbell wrote:
> In Xen 4.7 we are refactoring parts libxenctrl into a number of
> separate libraries which will provide backward and forward API and ABI
> compatiblity.
> 
> One such library will be libxenforeignmemory which provides access to
> privileged foreign mappings and which will provide an interface
> equivalent to xc_map_foreign_bulk.
> 
> In preparation for this switch all uses of xc_map_foreign_range to
> xc_map_foreign_bulk. 

The sentence is incomplete.

Unfortunately xc_map_foreign_bulk is not that well documented, but I am
assuming that the mfn parameter is not supposed to be changed by the
function, right?


> This is trivial because size was always
> XC_PAGE_SIZE so the necessary adjustments are trivial:
> 
>   * Pass &mfn (an array of length 1) instead of mfn
>   * Add a local err variable to receive the errors and pass &err
>     (again, an array of length 1)
>   * Adjust any existing logging to include err too
>   * Pass nr_pages=1 instead of size=XC_PAGE_SIZE
> 
> There is one wrinkle in xen_console.c:con_initialise() where
> con->ring_ref is an int but can in some code paths (when !xendev->dev)
> be treated as an mfn. I think this is an existing latent truncation
> hazard on platforms where xen_pfn_t is 64-bit and int is 32-bit (e.g.
> amd64, both arm* variants). I'm unsure under what circumstances
> xendev->dev can be NULL or if anything elsewhere ensures the value
> fits into an int. For now I just use a temporary xen_pfn_t to in
> effect upcast the pointer from int* to xen_pfn_t*.
> 
> Build tested with 4.0 and 4.5.
> 
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> ---
>  hw/char/xen_console.c |  9 +++++----
>  hw/display/xenfb.c    |  6 +++---
>  xen-hvm.c             | 29 +++++++++++++++--------------
>  3 files changed, 23 insertions(+), 21 deletions(-)
> 
> diff --git a/hw/char/xen_console.c b/hw/char/xen_console.c
> index c5a023c..6ef477a 100644
> --- a/hw/char/xen_console.c
> +++ b/hw/char/xen_console.c
> @@ -219,6 +219,7 @@ static int con_initialise(struct XenDevice *xendev)
>  {
>      struct XenConsole *con = container_of(xendev, struct XenConsole, xendev);
>      int limit;
> +    int err;
>  
>      if (xenstore_read_int(con->console, "ring-ref", &con->ring_ref) == -1)
>       return -1;
> @@ -228,10 +229,10 @@ static int con_initialise(struct XenDevice *xendev)
>       con->buffer.max_capacity = limit;
>  
>      if (!xendev->dev) {
> -        con->sring = xc_map_foreign_range(xen_xc, con->xendev.dom,
> -                                          XC_PAGE_SIZE,
> -                                          PROT_READ|PROT_WRITE,
> -                                          con->ring_ref);
> +     xen_pfn_t mfn = con->ring_ref;

indentation


> +        con->sring = xc_map_foreign_bulk(xen_xc, con->xendev.dom,
> +                                      PROT_READ|PROT_WRITE,
> +                                      &mfn, &err, 1);
>      } else {
>          con->sring = xengnttab_map_grant_ref(xendev->gnttabdev, 
> con->xendev.dom,
>                                               con->ring_ref,
> diff --git a/hw/display/xenfb.c b/hw/display/xenfb.c
> index 8a61e95..e3fdf33 100644
> --- a/hw/display/xenfb.c
> +++ b/hw/display/xenfb.c
> @@ -94,6 +94,7 @@ struct XenFB {
>  static int common_bind(struct common *c)
>  {
>      uint64_t mfn;
> +    int err;
>  
>      if (xenstore_read_fe_uint64(&c->xendev, "page-ref", &mfn) == -1)
>       return -1;
> @@ -102,9 +103,8 @@ static int common_bind(struct common *c)
>      if (xenstore_read_fe_int(&c->xendev, "event-channel", 
> &c->xendev.remote_port) == -1)
>       return -1;
>  
> -    c->page = xc_map_foreign_range(xen_xc, c->xendev.dom,
> -                                XC_PAGE_SIZE,
> -                                PROT_READ | PROT_WRITE, mfn);
> +    c->page = xc_map_foreign_bulk(xen_xc, c->xendev.dom,
> +                               PROT_READ | PROT_WRITE, &mfn, &err, 1);
>      if (c->page == NULL)
>       return -1;
>  
> diff --git a/xen-hvm.c b/xen-hvm.c
> index 54cbd72..3a56099 100644
> --- a/xen-hvm.c
> +++ b/xen-hvm.c
> @@ -1166,7 +1166,7 @@ static void xen_wakeup_notifier(Notifier *notifier, 
> void *data)
>  int xen_hvm_init(ram_addr_t *below_4g_mem_size, ram_addr_t 
> *above_4g_mem_size,
>                   MemoryRegion **ram_memory)
>  {
> -    int i, rc;
> +    int i, rc, map_err;
>      xen_pfn_t ioreq_pfn;
>      xen_pfn_t bufioreq_pfn;
>      evtchn_port_t bufioreq_evtchn;
> @@ -1213,33 +1213,34 @@ int xen_hvm_init(ram_addr_t *below_4g_mem_size, 
> ram_addr_t *above_4g_mem_size,
>      DPRINTF("buffered io page at pfn %lx\n", bufioreq_pfn);
>      DPRINTF("buffered io evtchn is %x\n", bufioreq_evtchn);
>  
> -    state->shared_page = xc_map_foreign_range(xen_xc, xen_domid, 
> XC_PAGE_SIZE,
> -                                              PROT_READ|PROT_WRITE, 
> ioreq_pfn);
> +    state->shared_page = xc_map_foreign_bulk(xen_xc, xen_domid,
> +                                          PROT_READ|PROT_WRITE,
> +                                          &ioreq_pfn, &map_err, 1);
>      if (state->shared_page == NULL) {
> -        hw_error("map shared IO page returned error %d handle=" 
> XC_INTERFACE_FMT,
> -                 errno, xen_xc);
> +        hw_error("map shared IO page returned error %d (%d) handle=" 
> XC_INTERFACE_FMT,
> +                 errno, map_err, xen_xc);
>      }
>  
>      rc = xen_get_vmport_regs_pfn(xen_xc, xen_domid, &ioreq_pfn);
>      if (!rc) {
>          DPRINTF("shared vmport page at pfn %lx\n", ioreq_pfn);
>          state->shared_vmport_page =
> -            xc_map_foreign_range(xen_xc, xen_domid, XC_PAGE_SIZE,
> -                                 PROT_READ|PROT_WRITE, ioreq_pfn);
> +             xc_map_foreign_bulk(xen_xc, xen_domid, PROT_READ|PROT_WRITE,
> +                                 &ioreq_pfn, &map_err, 1);
>          if (state->shared_vmport_page == NULL) {
> -            hw_error("map shared vmport IO page returned error %d handle="
> -                     XC_INTERFACE_FMT, errno, xen_xc);
> +            hw_error("map shared vmport IO page returned error %d (%d) 
> handle="
> +                     XC_INTERFACE_FMT, errno, map_err, xen_xc);
>          }
>      } else if (rc != -ENOSYS) {
>          hw_error("get vmport regs pfn returned error %d, rc=%d", errno, rc);
>      }
>  
> -    state->buffered_io_page = xc_map_foreign_range(xen_xc, xen_domid,
> -                                                   XC_PAGE_SIZE,
> -                                                   PROT_READ|PROT_WRITE,
> -                                                   bufioreq_pfn);
> +    state->buffered_io_page = xc_map_foreign_bulk(xen_xc, xen_domid,
> +                                               PROT_READ|PROT_WRITE,
> +                                                  &bufioreq_pfn,
> +                                               &map_err, 1);
>      if (state->buffered_io_page == NULL) {
> -        hw_error("map buffered IO page returned error %d", errno);
> +        hw_error("map buffered IO page returned error %d (%d)", errno, 
> map_err);
>      }
>  
>      /* Note: cpus is empty at this point in init */
> -- 
> 2.1.4
> 

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel