Re: linux PVH broken in 3.16.0-rc7 (arch_gnttab_map_shared)

[David Vrabel <david.vrabel@citrix.com>]

On 02/08/14 00:46, Mukesh Rathor wrote:
> Hi,
> 
> Not sure if this already got reported, but it appears 
> 
> commit b7dd0e3
> Author: David Vrabel <david.vrabel@citrix.com>
> Date:   Fri Jul 11 16:42:34 2014 +0100
> 
>     x86/xen: safely map and unmap grant frames when in atomic context
> 
> has broken boot of domU PVH. The reason being arch_gnttab_map_shared
> is getting called before gnttab_shared_vm_area gets initialized by
> arch_gnttab_init(). As the comment says,
> 
> --->
> /* Call it _before_ __gnttab_init as we need to initialize the
>  *  * xen_auto_xlat_grant_frames first. */
> core_initcall(xen_pvh_gnttab_setup);
> <---
> 
> we can't wait till arch_gnttab_init is called by __gnttab_init().

Does this fix it?  I can't test it because the only box I have easily
available for testing is AMD.

David

8<--------------------------------
x86/xen: use vmap() to map grant table pages in PVH guests

Commit b7dd0e350e0b (x86/xen: safely map and unmap grant frames when
in atomic context) causes PVH guests to crash in
arch_gnttab_map_shared() when they attempted to map the pages for the
grant table.

This use of a PV-specific function during the PVH grant table setup is
non-obvious and not needed.  The standard vmap() function does the
right thing.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reported-by: Mukesh Rathor <mukesh.rathor@oracle.com>
---
 arch/x86/xen/grant-table.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/xen/grant-table.c b/arch/x86/xen/grant-table.c
index ebfa9b2..767c9cb 100644
--- a/arch/x86/xen/grant-table.c
+++ b/arch/x86/xen/grant-table.c
@@ -168,6 +168,7 @@ static int __init xlated_setup_gnttab_pages(void)
 {
 	struct page **pages;
 	xen_pfn_t *pfns;
+	void *vaddr;
 	int rc;
 	unsigned int i;
 	unsigned long nr_grant_frames = gnttab_max_grant_frames();
@@ -193,21 +194,20 @@ static int __init xlated_setup_gnttab_pages(void)
 	for (i = 0; i < nr_grant_frames; i++)
 		pfns[i] = page_to_pfn(pages[i]);
 
-	rc = arch_gnttab_map_shared(pfns, nr_grant_frames, nr_grant_frames,
-				    &xen_auto_xlat_grant_frames.vaddr);
-
-	if (rc) {
+	vaddr = vmap(pages, nr_grant_frames, 0, PAGE_KERNEL);
+	if (!vaddr) {
 		pr_warn("%s Couldn't map %ld pfns rc:%d\n", __func__,
 			nr_grant_frames, rc);
 		free_xenballooned_pages(nr_grant_frames, pages);
 		kfree(pages);
 		kfree(pfns);
-		return rc;
+		return -ENOMEM;
 	}
 	kfree(pages);
 
 	xen_auto_xlat_grant_frames.pfn = pfns;
 	xen_auto_xlat_grant_frames.count = nr_grant_frames;
+	xen_auto_xlat_grant_frames.vaddr = vaddr;
 
 	return 0;
 }
-- 
1.7.10.4