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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <1217420e-42e4-9179-883f-125cf278caec@nvidia.com> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Content-Transfer-Encoding: quoted-printable Sender: linux-next-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-next@vger.kernel.org > Yes. Changes to mm/gup.c really should normally go through linux-mm and= =20 > Andrew's tree, if at all possible. This would have been caught, and fig= ured out > on linux-mm, had that been done--instead of leaving the linux-next main= tainer > trying to guess at how to resolve the conflict. >=20 > +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) :) >=20 > The fix-up below may (or may not) need some changes: >=20 >=20 > 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; > } > =20 > + /* try_grab_page() does nothing unless FOLL_GET or FOLL_PIN is set. = */ > + if (unlikely(!try_grab_page(page, flags))) { > + page =3D ERR_PTR(-ENOMEM); > + goto out; > + } > + if (flags & FOLL_GET) { >=20 >=20 > If I'm reading the diff correctly, I believe that line should *maybe* b= e changed to: >=20 > if (flags & (FOLL_GET | FOLL_PIN)) { >=20 > ...because each of those flags has a similar effect: pinned pages for D= MA 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=20 > arch_make_page_accessible() cause things like pin_user_pages() to not w= ork 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). >=20 > (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@de.ibm.co= m [2] https://lkml.kernel.org/r/20200224114107.4646-1-borntraeger@de.ibm.co= m --=20 Thanks, David / dhildenb