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Re: [Xen-devel] [PATCH v3 1/3] xen/arm: introduce XENFEAT_grant_map_identity

Hi Stefano,

On 01/08/14 15:56, Stefano Stabellini wrote:
The flag tells us that the hypervisor maps a grant page to guest
physical address == machine address of the page in addition to the
normal grant mapping address. It is needed to properly issue cache
maintenance operation at the completion of a DMA operation involving a
foreign grant.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Tested-by: Denis Schneider <v1ne2go@xxxxxxxxx>

Changes in v3:
- rename XENFEAT_grant_map_11 to XENFEAT_grant_map_identity.
  arch/arm/xen/enlighten.c         |    6 ++++++
  include/xen/interface/features.h |    3 +++
  2 files changed, 9 insertions(+)

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index b96723e..eef324f 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -262,6 +262,12 @@ static int __init xen_guest_init(void)
        xen_domain_type = XEN_HVM_DOMAIN;

+       if (!xen_feature(XENFEAT_grant_map_identity)) {
+               pr_warn("Please upgrade your Xen.\n"
+                               "If your platform has any non-coherent DMA devices, 
they won't work properly.\n");
+       }

I know we talked about this on a previous thread but I can't find it in my mail :/

Does a Linux with this series will work on Xen 4.4? If not what's the plan?

I think we have to keep any OS working on top on Xen 4.4 as people may want to retrieve the latest kernel for drivers bug fixes...

For running a previous kernel on Xen 4.5, then it will still be buggy. It might be worse to backport thise series on LTS kernel (i.e at least 3.14).


Julien Grall

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