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Tue, 19 Jan 2021 08:03:58 -0800 (PST) MIME-Version: 1.0 References: <20201127164131.2244124-1-daniel.vetter@ffwll.ch> <20201127164131.2244124-13-daniel.vetter@ffwll.ch> In-Reply-To: From: Daniel Vetter Date: Tue, 19 Jan 2021 17:03:47 +0100 Message-ID: Subject: Re: [PATCH v7 12/17] PCI: Revoke mappings like devmem To: Greg Kroah-Hartman Cc: DRI Development , LKML , Stephen Rothwell , KVM list , Linux MM , Linux ARM , linux-samsung-soc , "open list:DMA BUFFER SHARING FRAMEWORK" , Bjorn Helgaas , Dan Williams , Daniel Vetter , Jason Gunthorpe , Kees Cook , Andrew Morton , John Hubbard , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Jan Kara , Linux PCI Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Jan 19, 2021 at 4:20 PM Greg Kroah-Hartman wrote: > > On Tue, Jan 19, 2021 at 03:34:47PM +0100, Daniel Vetter wrote: > > On Tue, Jan 19, 2021 at 3:32 PM Greg Kroah-Hartman > > wrote: > > > > > > On Tue, Jan 19, 2021 at 09:17:55AM +0100, Daniel Vetter wrote: > > > > On Fri, Nov 27, 2020 at 5:42 PM Daniel Vetter wrote: > > > > > > > > > > Since 3234ac664a87 ("/dev/mem: Revoke mappings when a driver clai= ms > > > > > the region") /dev/kmem zaps ptes when the kernel requests exclusi= ve > > > > > acccess to an iomem region. And with CONFIG_IO_STRICT_DEVMEM, thi= s is > > > > > the default for all driver uses. > > > > > > > > > > Except there's two more ways to access PCI BARs: sysfs and proc m= map > > > > > support. Let's plug that hole. > > > > > > > > > > For revoke_devmem() to work we need to link our vma into the same > > > > > address_space, with consistent vma->vm_pgoff. ->pgoff is already > > > > > adjusted, because that's how (io_)remap_pfn_range works, but for = the > > > > > mapping we need to adjust vma->vm_file->f_mapping. The cleanest w= ay is > > > > > to adjust this at at ->open time: > > > > > > > > > > - for sysfs this is easy, now that binary attributes support this= . We > > > > > just set bin_attr->mapping when mmap is supported > > > > > - for procfs it's a bit more tricky, since procfs pci access has = only > > > > > one file per device, and access to a specific resources first n= eeds > > > > > to be set up with some ioctl calls. But mmap is only supported = for > > > > > the same resources as sysfs exposes with mmap support, and othe= rwise > > > > > rejected, so we can set the mapping unconditionally at open tim= e > > > > > without harm. > > > > > > > > > > A special consideration is for arch_can_pci_mmap_io() - we need t= o > > > > > make sure that the ->f_mapping doesn't alias between ioport and i= omem > > > > > space. There's only 2 ways in-tree to support mmap of ioports: ge= neric > > > > > pci mmap (ARCH_GENERIC_PCI_MMAP_RESOURCE), and sparc as the singl= e > > > > > architecture hand-rolling. Both approach support ioport mmap thro= ugh a > > > > > special pfn range and not through magic pte attributes. Aliasing = is > > > > > therefore not a problem. > > > > > > > > > > The only difference in access checks left is that sysfs PCI mmap = does > > > > > not check for CAP_RAWIO. I'm not really sure whether that should = be > > > > > added or not. > > > > > > > > > > Acked-by: Bjorn Helgaas > > > > > Reviewed-by: Dan Williams > > > > > Signed-off-by: Daniel Vetter > > > > > Cc: Jason Gunthorpe > > > > > Cc: Kees Cook > > > > > Cc: Dan Williams > > > > > Cc: Andrew Morton > > > > > Cc: John Hubbard > > > > > Cc: J=C3=A9r=C3=B4me Glisse > > > > > Cc: Jan Kara > > > > > Cc: Dan Williams > > > > > Cc: Greg Kroah-Hartman > > > > > Cc: linux-mm@kvack.org > > > > > Cc: linux-arm-kernel@lists.infradead.org > > > > > Cc: linux-samsung-soc@vger.kernel.org > > > > > Cc: linux-media@vger.kernel.org > > > > > Cc: Bjorn Helgaas > > > > > Cc: linux-pci@vger.kernel.org > > > > > Signed-off-by: Daniel Vetter > > > > > -- > > > > > v2: > > > > > - Totally new approach: Adjust filp->f_mapping at open time. Note= that > > > > > this now works on all architectures, not just those support > > > > > ARCH_GENERIC_PCI_MMAP_RESOURCE > > > > > --- > > > > > drivers/pci/pci-sysfs.c | 4 ++++ > > > > > drivers/pci/proc.c | 1 + > > > > > 2 files changed, 5 insertions(+) > > > > > > > > > > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c > > > > > index d15c881e2e7e..3f1c31bc0b7c 100644 > > > > > --- a/drivers/pci/pci-sysfs.c > > > > > +++ b/drivers/pci/pci-sysfs.c > > > > > @@ -929,6 +929,7 @@ void pci_create_legacy_files(struct pci_bus *= b) > > > > > b->legacy_io->read =3D pci_read_legacy_io; > > > > > b->legacy_io->write =3D pci_write_legacy_io; > > > > > b->legacy_io->mmap =3D pci_mmap_legacy_io; > > > > > + b->legacy_io->mapping =3D iomem_get_mapping(); > > > > > pci_adjust_legacy_attr(b, pci_mmap_io); > > > > > error =3D device_create_bin_file(&b->dev, b->legacy_io); > > > > > if (error) > > > > > @@ -941,6 +942,7 @@ void pci_create_legacy_files(struct pci_bus *= b) > > > > > b->legacy_mem->size =3D 1024*1024; > > > > > b->legacy_mem->attr.mode =3D 0600; > > > > > b->legacy_mem->mmap =3D pci_mmap_legacy_mem; > > > > > + b->legacy_io->mapping =3D iomem_get_mapping(); > > > > > > > > Unlike the normal pci stuff below, the legacy files here go boom > > > > because they're set up much earlier in the boot sequence. This only > > > > affects HAVE_PCI_LEGACY architectures, which aren't that many. So w= hat > > > > should we do here now: > > > > - drop the devmem revoke for these > > > > - rework the init sequence somehow to set up these files a lot late= r > > > > - redo the sysfs patch so that it doesn't take an address_space > > > > pointer, but instead a callback to get at that (since at open time > > > > everything is set up). Imo rather ugly > > > > - ditch this part of the series (since there's not really any taker= s > > > > for the latter parts it might just not make sense to push for this) > > > > - something else? > > > > > > > > Bjorn, Greg, thoughts? > > > > > > What sysfs patch are you referring to here? > > > > Currently in linux-next: > > > > commit 74b30195395c406c787280a77ae55aed82dbbfc7 (HEAD -> > > topic/iomem-mmap-vs-gup, drm/topic/iomem-mmap-vs-gup) > > Author: Daniel Vetter > > Date: Fri Nov 27 17:41:25 2020 +0100 > > > > sysfs: Support zapping of binary attr mmaps > > > > Or the patch right before this one in this submission here: > > > > https://lore.kernel.org/dri-devel/20201127164131.2244124-12-daniel.vett= er@ffwll.ch/ > > Ah. Hm, a callback in the sysfs file logic seems really hairy, so I > would prefer that not happen. If no one really needs this stuff, why > not just drop it like you mention? Well it is needed, but just on architectures I don't care about much. Most relevant is perhaps powerpc (that's where Stephen hit the issue). I do wonder whether we could move the legacy pci files setup to where the modern stuff is set up from pci_create_resource_files() or maybe pci_create_sysfs_dev_files() even for HAVE_PCI_LEGACY. I think that might work, but since it's legacy flow on some funny architectures (alpha, itanium, that kind of stuff) I have no idea what kind of monsters I'm going to anger :-) -Daniel --=20 Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch