> Yes. Changes to mm/gup.c really should normally go through linux-mm and > Andrew's tree, if at all possible. This would have been caught, and figured out > on linux-mm, had that been done--instead of leaving the linux-next maintainer > trying to guess at how to resolve the conflict. > > +Cc David Hildenbrand, who I see looked at the kvms390 proposed patch a bit. > Maybe he has some opinions, especially about my questions below. I'll leave figuring out the details to Christian/Claudio (-EBUSY) :) > > The fix-up below may (or may not) need some changes: > > > diff --cc mm/gup.c > index 354bcfbd844b,f589299b0d4a..000000000000 > --- a/mm/gup.c > +++ b/mm/gup.c > @@@ -269,18 -470,11 +468,19 @@@ retry > goto retry; > } > > + /* try_grab_page() does nothing unless FOLL_GET or FOLL_PIN is set. */ > + if (unlikely(!try_grab_page(page, flags))) { > + page = ERR_PTR(-ENOMEM); > + goto out; > + } > + if (flags & FOLL_GET) { > > > If I'm reading the diff correctly, I believe that line should *maybe* be changed to: > > if (flags & (FOLL_GET | FOLL_PIN)) { > > ...because each of those flags has a similar effect: pinned pages for DMA or RDMA > use. So either flag will require a call to arch_make_page_accessible()...except that > I'm not sure that's what you want. Would the absence of a call to > arch_make_page_accessible() cause things like pin_user_pages() to not work correctly? > Seems like it would, to me. Yes, it's required. From the commit message "enable paging, file backing etc, it is also necessary to protect the host against a malicious user space. For example a bad QEMU could simply start direct I/O on such protected memory.". So we really want to convert the page from unencrypted/inaccessible to encrypted/accessible at this point (iow, make it definitely accessible, and make sure it stays accessible). > > (I'm pretty unhappy that we have to ask this at the linux-next level.) Yeah, I *think* this fell through the cracks (on linux-mm, but also in Andrew's inbox) because the series has a big fat "KVM: s390:" as prefix. Christian decided to pull it in to give it some churn yesterday (I think he originally wanted to have this patch and the other KVM protvirt patches in 5.7 [2] ... but not sure what will happen due to this conflict). At least now this patch has attention ... although it would have been better if linux-next admins wouldn't have to mess with this :) [1] https://lkml.kernel.org/r/20200224114107.4646-2-borntraeger@xxxxxxxxxx [2] https://lkml.kernel.org/r/20200224114107.4646-1-borntraeger@xxxxxxxxxx -- Thanks, David / dhildenb