[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Re: [PATCH 5/7] mm: New XENMEM space, XENMAPSPACE_gmfn_range
>>> On 11.11.11 at 10:13, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote: > On Fri, 2011-11-11 at 08:09 +0000, Jan Beulich wrote: >> >>> On 10.11.11 at 18:37, Jean Guyader <jean.guyader@xxxxxxxxxxxxx> wrote: >> > On 10/11 12:47, Jan Beulich wrote: >> >> >>> On 10.11.11 at 12:35, Jean Guyader <jean.guyader@xxxxxxxxxxxxx> wrote: >> >> >@@ -4716,6 +4748,17 @@ long arch_memory_op(int op, >> >> >XEN_GUEST_HANDLE(void) >> > arg) >> >> > } >> >> > >> >> > rc = xenmem_add_to_physmap(d, &xatp); >> >> >+ if ( rc == -EAGAIN ) >> >> >> >> if ( rc ) >> >> >> >> >+ { >> >> >+ if ( copy_to_guest(arg, &xatp, 1) ) >> >> >+ { >> >> >+ rcu_unlock_domain(d); >> >> >+ return -EFAULT; >> >> >+ } >> >> >> >> } >> >> if ( rc == -EAGAIN ) >> >> >> >> (with some room for further simplification). Without that (or the minimal >> >> alternative of copying back just .size or yet some other mechanism), as >> >> pointed out before, the caller won't have a way to know how far into >> >> the batch things succeeded. >> >> >> > >> > In xenmem_add_to_physmap I modify xatp in place so when I exit this >> > function xatp will contain the updated value (new start value in >> > .gpfn and .idx, how far do I need to go in .size). >> > >> > The idea here was to call the copy_to_guest only when we got preempted. >> > If I copy xatp back to the guest I should get the updated value >> > in xatp from the copy_from_guest when I'll be called by the continuation. >> >> I understand the continuation aspect. But you appear to have not read >> my comments completely: I'm asking how your caller, in the event of >> failure, would know how much of the batch was processed successfully. > > For this sort of flush operation can the caller assume that failure > means nothing was flushed, since a flush can always be repeated? This is not just a flush - instead, the flush is just a necessary sub- operation of what is being done here. I don't think the actual add- to-physmap should be repeated. And even if it can, at least for diagnostic/debugging purposes knowing where things failed is rather useful. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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