Re: [Xen-devel] [PATCH] xen-blkfront: set pages are FOREIGN_FRAME when sharing them

[Konrad Rzeszutek Wilk <konrad@darnok.org>]

On Tue, Mar 27, 2012 at 02:49:58PM +0100, Stefano Stabellini wrote:
> Set pages as FOREIGN_FRAME whenever blkfront shares them with another
> domain. Then when blkfront un-share them, also removes the
> FOREIGN_FRAME_BIT from the p2m.
> 
> We do it so that when the source and the destination domain are the same
> (blkfront connected to blkback in the same domain) we can more easily
> recognize which ones are the source pfns and which ones are the
> destination pfns (both are going to be pointing to the same mfns).
> 
> Without this patch enstablishing a connection between blkfront and QEMU
> qdisk in the same domain causes QEMU to hang and never return.
> Considering that it fixes a serious bug, it should be backported to
> previous releases.


ERROR: "set_phys_to_machine" [drivers/block/xen-blkfront.ko] undefined!

> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> ---
>  drivers/block/xen-blkfront.c |   30 +++++++++++++++++++++++++-----
>  1 files changed, 25 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 2f22874..e027aa7 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -262,7 +262,7 @@ static int blkif_ioctl(struct block_device *bdev, fmode_t mode,
>  static int blkif_queue_request(struct request *req)
>  {
>  	struct blkfront_info *info = req->rq_disk->private_data;
> -	unsigned long buffer_mfn;
> +	unsigned long buffer_mfn, buffer_pfn;
>  	struct blkif_request *ring_req;
>  	unsigned long id;
>  	unsigned int fsect, lsect;
> @@ -321,7 +321,8 @@ static int blkif_queue_request(struct request *req)
>  		       BLKIF_MAX_SEGMENTS_PER_REQUEST);
>  
>  		for_each_sg(info->sg, sg, ring_req->u.rw.nr_segments, i) {
> -			buffer_mfn = pfn_to_mfn(page_to_pfn(sg_page(sg)));
> +			buffer_pfn = page_to_pfn(sg_page(sg));
> +			buffer_mfn = pfn_to_mfn(buffer_pfn);
>  			fsect = sg->offset >> 9;
>  			lsect = fsect + (sg->length >> 9) - 1;
>  			/* install a grant reference. */
> @@ -340,6 +341,16 @@ static int blkif_queue_request(struct request *req)
>  						.gref       = ref,
>  						.first_sect = fsect,
>  						.last_sect  = lsect };
> +			/* 
> +			 * Set the page as foreign, considering that we are giving
> +			 * it to a foreign domain.
> +			 * This is important in case the destination domain is
> +			 * ourselves, so that we can more easily recognize the
> +			 * source pfn from destination pfn, both mapping to the same
> +			 * mfn.
> +			 */
> +			set_phys_to_machine(buffer_pfn,
> +					FOREIGN_FRAME(buffer_mfn));
>  		}
>  	}
>  
> @@ -715,8 +726,11 @@ static void blkif_completion(struct blk_shadow *s)
>  	int i;
>  	/* Do not let BLKIF_OP_DISCARD as nr_segment is in the same place
>  	 * flag. */
> -	for (i = 0; i < s->req.u.rw.nr_segments; i++)
> +	for (i = 0; i < s->req.u.rw.nr_segments; i++) {
>  		gnttab_end_foreign_access(s->req.u.rw.seg[i].gref, 0, 0UL);
> +		set_phys_to_machine(s->frame[i],
> +				get_phys_to_machine(s->frame[i]) & ~FOREIGN_FRAME_BIT);
> +	}
>  }
>  
>  static irqreturn_t blkif_interrupt(int irq, void *dev_id)
> @@ -1051,13 +1065,19 @@ static int blkif_recover(struct blkfront_info *info)
>  		memcpy(&info->shadow[req->u.rw.id], &copy[i], sizeof(copy[i]));
>  
>  		if (req->operation != BLKIF_OP_DISCARD) {
> +			unsigned long buffer_pfn;
> +			unsigned long buffer_mfn;
>  		/* Rewrite any grant references invalidated by susp/resume. */
> -			for (j = 0; j < req->u.rw.nr_segments; j++)
> +			for (j = 0; j < req->u.rw.nr_segments; j++) {
> +				buffer_pfn = info->shadow[req->u.rw.id].frame[j];
> +				buffer_mfn = pfn_to_mfn(buffer_pfn);
>  				gnttab_grant_foreign_access_ref(
>  					req->u.rw.seg[j].gref,
>  					info->xbdev->otherend_id,
> -					pfn_to_mfn(info->shadow[req->u.rw.id].frame[j]),
> +					buffer_mfn,
>  					rq_data_dir(info->shadow[req->u.rw.id].request));
> +				set_phys_to_machine(buffer_pfn, FOREIGN_FRAME(buffer_mfn));
> +			}
>  		}
>  		info->shadow[req->u.rw.id].req = *req;
>  
> -- 
> 1.7.2.5
> 
> 
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