On 09/09/14 13:50, Tamas K Lengyel wrote: > > > On Mon, Sep 8, 2014 at 10:47 PM, Tamas K Lengyel > > wrote: > > > On Mon, Sep 8, 2014 at 10:43 PM, Julien Grall > > wrote: > > Hello Tamas, > > On 03/09/14 02:00, Tamas K Lengyel wrote: > > > > > On Wed, Sep 3, 2014 at 10:44 AM, Ian Campbell > > >> wrote: > > On Mon, 2014-09-01 at 17:32 -0400, Julien Grall wrote: > > Hi Ian, > > > > On 16/07/14 12:02, Ian Campbell wrote: > > > I'd much prefer to just have the fix to > xc_dom_gnttab_hvm_seed > for ARM > > > and continue to punt on this interface until it > is actually > needed by > > > something unavoidable on the guest side (and > simultaneously > hope that > > > day never comes...). > > > > This patch is a requirement to make Xen Memory > access working on ARM. > > Could you reconsider the possibility to apply this > patch on Xen? > > Needs more rationale as to why it is required for Xen > Memory (do you > mean xenaccess?). I assume I'll find that in the > relevant thread once I > get to it? > > > It's used in a non-critical sanity check for performance > reasons, as > seen here: > https://github.com/tklengyel/xen/blob/arm_memaccess3/xen/common/mem_access.c#L75. > Without the sanity check we might attempt to set > mem_access permissions > on gpfn's that don't exist for the guest. It wouldn't > break anything to > do that but if we know beforehand that the gpfn is outside > the scope of > what the guest has we can skip the entire thing. > > > It might be better if you carry this patch on your series. > > Regards, > > -- > Julien Grall > > > Alright. > > Thanks, > Tamas > > > As a sidenote, if this patch is problematic to merge for some reason, > the current implementation still needs to change to return 0 instead > of -ENOSYS as to conform to the x86 implementation. On the x86 side 0 > is used to indicate failure. See > 7ffc9779aa5120c5098d938cb88f69a1dda9a0fe "x86: make certain memory > sub-ops return valid values" for more info. 0 does not indicate failure. It indicates the value held in the shared info field, which if 0, indicates that the domain is still being built by the toolstack. -ENOSYS is still a valid failure case. ~Andrew