Messages in this thread | | | Date | Mon, 21 Aug 2023 14:55:01 -0500 | From | Bjorn Helgaas <> | Subject | Re: [RESEND PATCH v2 2/2] PCI: implement custom llseek method for PCI resource entries in sysfs |
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In subject, to match history:
PCI: Implement custom llseek for sysfs resource entries
On Mon, Aug 21, 2023 at 12:29:56PM +0500, Valentine Sinitsyn wrote: > Since commit 636b21b50152 ("PCI: Revoke mappings like devmem"), mmapable > sysfs entries have started to receive their f_mapping from the iomem > pseudo filesystem, so that CONFIG_IO_STRICT_DEVMEM is honored in sysfs > (and procfs) as well as in /dev/[k]mem.
s/mmapable/mmappable/ (there's precedent for both, but by analogy with "mappable", I think "mmappable" makes more sense)
> This resulted in a userspace-visible regression: > > 1. Open a sysfs PCI resource file (eg. /sys/bus/pci/devices/*/resource0) > 2. Use lseek(fd, 0, SEEK_END) to determine its size > > Expected result: a PCI region size is returned. > Actual result: 0 is returned. > > The reason is that PCI resource files residing in sysfs use > generic_file_llseek(), which relies on f_mapping->host inode to get the > file size. As f_mapping is now redefined, f_mapping->host points to an > anonymous zero-sized iomem_inode which has nothing to do with sysfs file > in question. > > Implement a custom llseek method for sysfs PCI resources, which is > almost the same as proc_bus_pci_lseek() used for procfs entries. > > This makes sysfs and procfs entries consistent with regards to seeking, > but also introduces userspace-visible changes to seeking PCI resources > in sysfs: > > - SEEK_DATA and SEEK_HOLE are no longer supported; > - Seeking past the end of the file is prohibited while previously > offsets up to MAX_NON_LFS were accepted (reading from these offsets > was always invalid). > > Fixes: 636b21b50152 ("PCI: Revoke mappings like devmem") > Cc: stable@vger.kernel.org > Signed-off-by: Valentine Sinitsyn <valesini@yandex-team.ru>
It'd be nice but not essential to tweak commit log as above.
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
> --- > Looks like the patch didn't get to lkml, resending > > drivers/pci/pci-sysfs.c | 21 ++++++++++++++++++++- > 1 file changed, 20 insertions(+), 1 deletion(-) > > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c > index ab32a91f287b..42eaeb8d4a4f 100644 > --- a/drivers/pci/pci-sysfs.c > +++ b/drivers/pci/pci-sysfs.c > @@ -967,6 +967,8 @@ void pci_create_legacy_files(struct pci_bus *b) > b->legacy_io->attr.mode = 0600; > b->legacy_io->read = pci_read_legacy_io; > b->legacy_io->write = pci_write_legacy_io; > + /* See pci_create_attr() for motivation */ > + b->legacy_io->llseek = pci_llseek_resource; > b->legacy_io->mmap = pci_mmap_legacy_io; > b->legacy_io->f_mapping = iomem_get_mapping; > pci_adjust_legacy_attr(b, pci_mmap_io); > @@ -981,6 +983,8 @@ void pci_create_legacy_files(struct pci_bus *b) > b->legacy_mem->size = 1024*1024; > b->legacy_mem->attr.mode = 0600; > b->legacy_mem->mmap = pci_mmap_legacy_mem; > + /* See pci_create_attr() for motivation */ > + b->legacy_io->llseek = pci_llseek_resource; > b->legacy_mem->f_mapping = iomem_get_mapping; > pci_adjust_legacy_attr(b, pci_mmap_mem); > error = device_create_bin_file(&b->dev, b->legacy_mem); > @@ -1138,6 +1142,14 @@ static ssize_t pci_write_resource_io(struct file *filp, struct kobject *kobj, > return pci_resource_io(filp, kobj, attr, buf, off, count, true); > } > > +static loff_t pci_llseek_resource(struct file *filep, > + struct kobject *kobj __always_unused, > + struct bin_attribute *attr, > + loff_t offset, int whence) > +{ > + return fixed_size_llseek(filep, offset, whence, attr->size); > +} > + > /** > * pci_remove_resource_files - cleanup resource files > * @pdev: dev to cleanup > @@ -1195,8 +1207,15 @@ static int pci_create_attr(struct pci_dev *pdev, int num, int write_combine) > res_attr->mmap = pci_mmap_resource_uc; > } > } > - if (res_attr->mmap) > + if (res_attr->mmap) { > res_attr->f_mapping = iomem_get_mapping; > + /* > + * generic_file_llseek() consults f_mapping->host to determine > + * the file size. As iomem_inode knows nothing about the > + * attribute, it's not going to work, so override it as well. > + */ > + res_attr->llseek = pci_llseek_resource; > + } > res_attr->attr.name = res_attr_name; > res_attr->attr.mode = 0600; > res_attr->size = pci_resource_len(pdev, num); > -- > 2.34.1 >
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