[Xen-devel] [PATCH for-4.6] tools/libxc: linux: Don't use getpagesize() when unmapping the grants

[Julien Grall <julien.grall@xxxxxxxxxx>]

The grants are based on the Xen granularity (i.e 4KB). While the function
to map grants for Linux (linux_gnttab_grant_map) is using the correct
size (XC_PAGE_SIZE), the unmap one (linux_gnttab_munmap) is using
getpagesize().

On domain using a page granularity different than Xen (this is the case
for AARCH64 guest using 64KB page), the unmap will be called with the
wrong size.

Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>

---
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>

    This is a candidate for Xen 4.6 and backport for Xen 4.5.
    There is no functional changes for 4KB domain (i.e x86, arm32, arm64 when
    4KB is used) but fixes a latent problem when the domain is using 64KB page
    on ARM64.

    The mmap is done correctly use XC_PAGE_SIZE but not the munmap.
    This will likely fail to unmap. I don't think it will unmap too
    much.

    I grepped getpagesize in the tools, and so far I haven't found any other
    in Xen specific code. There is some in blktap2 and QEMU. I don't think
    the former is that important for ARM64. I will take care of the latter
    in a separate series.
---
 tools/libxc/xc_linux_osdep.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/libxc/xc_linux_osdep.c b/tools/libxc/xc_linux_osdep.c
index e375428..76c55ff 100644
--- a/tools/libxc/xc_linux_osdep.c
+++ b/tools/libxc/xc_linux_osdep.c
@@ -742,7 +742,7 @@ static int linux_gnttab_munmap(xc_gnttab *xcg, 
xc_osdep_handle h,
     }
 
     /* Next, unmap the memory. */
-    if ( (rc = munmap(start_address, count * getpagesize())) )
+    if ( (rc = munmap(start_address, count * XC_PAGE_SIZE)) )
         return rc;
 
     /* Finally, unmap the driver slots used to store the grant information. */
-- 
2.1.4


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