Re: [Qemu-devel] [RFC v2 19/32] vhost+postcopy: Resolve client address

[Peter Xu]

On Thu, Aug 24, 2017 at 08:27:17PM +0100, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <address@hidden>
> 
> Resolve fault addresses read off the clients UFD into RAMBlock
> and offset, and call back to the postcopy code to ask for the page.
> 
> Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> ---
>  hw/virtio/trace-events |  3 +++
>  hw/virtio/vhost-user.c | 30 +++++++++++++++++++++++++++++-
>  2 files changed, 32 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/virtio/trace-events b/hw/virtio/trace-events
> index 5067dee19b..f7d4b831fe 100644
> --- a/hw/virtio/trace-events
> +++ b/hw/virtio/trace-events
> @@ -1,6 +1,9 @@
>  # See docs/devel/tracing.txt for syntax documentation.
>  
>  # hw/virtio/vhost-user.c
> +vhost_user_postcopy_fault_handler(const char *name, uint64_t fault_address, 
> int nregions) "%s: @0x%"PRIx64" nregions:%d"
> +vhost_user_postcopy_fault_handler_loop(int i, uint64_t client_base, uint64_t 
> size) "%d: client 0x%"PRIx64" +0x%"PRIx64
> +vhost_user_postcopy_fault_handler_found(int i, uint64_t region_offset, 
> uint64_t rb_offset) "%d: region_offset: 0x%"PRIx64" rb_offset:0x%"PRIx64
>  vhost_user_postcopy_listen(void) ""
>  vhost_user_set_mem_table_postcopy(uint64_t client_addr, uint64_t qhva, int 
> reply_i, int region_i) "client:0x%"PRIx64" for hva: 0x%"PRIx64" reply %d 
> region %d"
>  vhost_user_set_mem_table_withfd(int index, const char *name, uint64_t 
> memory_size, uint64_t guest_phys_addr, uint64_t userspace_addr, uint64_t 
> offset) "%d:%s: size:0x%"PRIx64" GPA:0x%"PRIx64" QVA/userspace:0x%"PRIx64" RB 
> offset:0x%"PRIx64
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index fbe2743298..2897ff70b3 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -816,7 +816,35 @@ out:
>  static int vhost_user_postcopy_fault_handler(struct PostCopyFD *pcfd,
>                                               void *ufd)
>  {
> -    return 0;
> +    struct vhost_dev *dev = pcfd->data;
> +    struct vhost_user *u = dev->opaque;
> +    struct uffd_msg *msg = ufd;
> +    uint64_t faultaddr = msg->arg.pagefault.address;
> +    RAMBlock *rb = NULL;
> +    uint64_t rb_offset;
> +    int i;
> +
> +    trace_vhost_user_postcopy_fault_handler(pcfd->idstr, faultaddr,
> +                                            dev->mem->nregions);
> +    for (i = 0; i < MIN(dev->mem->nregions, u->region_rb_len); i++) {

Should dev->mem->nregions always the same as u->region_rb_len?

> +        trace_vhost_user_postcopy_fault_handler_loop(i,
> +                u->postcopy_client_bases[i], 
> dev->mem->regions[i].memory_size);
> +        if (faultaddr >= u->postcopy_client_bases[i]) {
> +            /* Ofset of the fault address in the vhost region */
> +            uint64_t region_offset = faultaddr - u->postcopy_client_bases[i];
> +            if (region_offset <= dev->mem->regions[i].memory_size) {

Should be "<" rather than "<="?  Say:

Region 1: [0, 1M), size 1M
Region 2: [1M, 2M), size 1M

Looks like otherwise faultaddr=1M will fall into region 1, while it
should be region 2?

> +                rb_offset = region_offset + u->region_rb_offset[i];
> +                trace_vhost_user_postcopy_fault_handler_found(i,
> +                        region_offset, rb_offset);
> +                rb = u->region_rb[i];

Nit: this "rb" might be avoided if only used once.

> +                return postcopy_request_shared_page(pcfd, rb, faultaddr,
> +                                                    rb_offset);
> +            }
> +        }
> +    }
> +    error_report("%s: Failed to find region for fault %" PRIx64,
> +                 __func__, faultaddr);
> +    return -1;
>  }
>  
>  /*
> -- 
> 2.13.5
> 

-- 
Peter Xu