Linux Virtualization - Sep 2019 - [PATCH] vhost: Fix compile time error

Building vhost on 32-bit targets results in the following error.

drivers/vhost/vhost.c: In function 'translate_desc':
include/linux/compiler.h:549:38: error:
	call to '__compiletime_assert_1879' declared with attribute error:
	BUILD_BUG_ON failed: sizeof(_s) > sizeof(long)

Fixes: a89db445fbd7 ("vhost: block speculation of translated
descriptors")
Cc: Michael S. Tsirkin <mst at redhat.com>
Cc: Jason Wang <jasowang at redhat.com>
Signed-off-by: Guenter Roeck <linux at roeck-us.net>
---
 drivers/vhost/vhost.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index acabf20b069e..102a0c877007 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2074,7 +2074,7 @@ static int translate_desc(struct vhost_virtqueue *vq, u64
addr, u32 len,
 		_iov->iov_base = (void __user *)
 			((unsigned long)node->userspace_addr +
 			 array_index_nospec((unsigned long)(addr - node->start),
-					    node->size));
+					    (unsigned long)node->size));
 		s += size;
 		addr += size;
 		++ret;
-- 
2.7.4

On Sat, Sep 14, 2019 at 01:44:57AM -0700, Guenter Roeck
wrote:
> Building vhost on 32-bit targets results in the following error.
> 
> drivers/vhost/vhost.c: In function 'translate_desc':
> include/linux/compiler.h:549:38: error:
> 	call to '__compiletime_assert_1879' declared with attribute error:
> 	BUILD_BUG_ON failed: sizeof(_s) > sizeof(long)
> 
> Fixes: a89db445fbd7 ("vhost: block speculation of translated
descriptors")
> Cc: Michael S. Tsirkin <mst at redhat.com>
> Cc: Jason Wang <jasowang at redhat.com>
> Signed-off-by: Guenter Roeck <linux at roeck-us.net>

> ---
>  drivers/vhost/vhost.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index acabf20b069e..102a0c877007 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -2074,7 +2074,7 @@ static int translate_desc(struct vhost_virtqueue *vq,
u64 addr, u32 len,
>  		_iov->iov_base = (void __user *)
>  			((unsigned long)node->userspace_addr +
>  			 array_index_nospec((unsigned long)(addr - node->start),
> -					    node->size));
> +					    (unsigned long)node->size));
Unfortunately this does not fix the case where size is actually 64 bit,
e.g. a single node with VA 0, size 2^32 is how
you cover the whole virtual address space.

this is not how qemu uses it, but it's valid.

I think it's best to just revert the patch for now.
>  		s += size;
>  		addr += size;
>  		++ret;
> -- 
> 2.7.4