On Tue, 13 Aug 2013, Konrad Rzeszutek Wilk wrote: > On Tue, Aug 13, 2013 at 12:17:18PM +0100, Stefano Stabellini wrote: > > On Fri, 9 Aug 2013, Konrad Rzeszutek Wilk wrote: > > > On Sun, Aug 04, 2013 at 03:39:41PM +0100, Stefano Stabellini wrote: > > > > GNTTABOP_unmap_grant_ref unmaps a grant and replaces it with a 0 > > > > mapping instead of reinstating the original mapping. > > > > Doing so separately would be racy. > > > > > > > > To unmap a grant and reinstate the original mapping atomically we use > > > > GNTTABOP_unmap_and_replace. > > > > GNTTABOP_unmap_and_replace doesn't work with GNTMAP_contains_pte, so > > > > don't use it for kmaps. GNTTABOP_unmap_and_replace zeroes the mapping > > > > passed in new_addr so we have to reinstate it, however that is a > > > > per-cpu mapping only used for balloon scratch pages, so we can be sure > > > > that > > > > it's not going to be accessed while the mapping is not valid. > > > > > > This looks to be depend on a new structure, which is not in Linux kernel? > > > Are you missing a dependency patch? > > > > Nope, GNTTABOP_unmap_and_replace and struct gnttab_unmap_and_replace are > > already present in include/xen/interface/grant_table.h. > > > > > > > Shouldn't we use some logic to figure out which hypercall to use if the > > > hypervisor does not support it? > > > > GNTTABOP_unmap_and_replace is not a new hypercall, it has been supported > > by Xen for a very long time. > > > > In a previous iteration of this patch series, I did introduce a new > > hypercall, but then I dropped it because I figured out that I could > > achieve the same thing with the existing hypercall. > > OK, Please tack on: > > Acked-by: Konrad Rzeszutek Wilk <konrad.w...@oracle.com> > > P.S. > If you could stick it on devel/for-linus-3.12 that would be super. Thanks!
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