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Commit47c8846a49("PCI: Extend ACS configurability") introduced bugs that fail to configure ACS ctrl to the value specified by the kernel parameter. Essentially there are two bugs: 1) When ACS is configured for multiple PCI devices using 'config_acs' kernel parameter, it results into error "PCI: Can't parse ACS command line parameter". This is due to a bug that doesn't preserve the ACS mask, but instead overwrites the mask with value 0. For example, using 'config_acs' to configure ACS ctrl for multiple BDFs fails: Kernel command line: pci=config_acs=1111011@0020:02:00.0;101xxxx@0039:00:00.0 "dyndbg=file drivers/pci/pci.c +p" PCI: Can't parse ACS command line parameter pci 0020:02:00.0: ACS mask = 0x007f pci 0020:02:00.0: ACS flags = 0x007b pci 0020:02:00.0: Configured ACS to 0x007b After this fix: Kernel command line: pci=config_acs=1111011@0020:02:00.0;101xxxx@0039:00:00.0 "dyndbg=file drivers/pci/pci.c +p" pci 0020:02:00.0: ACS mask = 0x007f pci 0020:02:00.0: ACS flags = 0x007b pci 0020:02:00.0: ACS control = 0x005f pci 0020:02:00.0: ACS fw_ctrl = 0x0053 pci 0020:02:00.0: Configured ACS to 0x007b pci 0039:00:00.0: ACS mask = 0x0070 pci 0039:00:00.0: ACS flags = 0x0050 pci 0039:00:00.0: ACS control = 0x001d pci 0039:00:00.0: ACS fw_ctrl = 0x0000 pci 0039:00:00.0: Configured ACS to 0x0050 2) In the bit manipulation logic, we copy the bit from the firmware settings when mask bit 0. For example, 'disable_acs_redir' fails to clear all three ACS P2P redir bits due to the wrong bit fiddling: Kernel command line: pci=disable_acs_redir=0020:02:00.0;0030:02:00.0;0039:00:00.0 "dyndbg=file drivers/pci/pci.c +p" pci 0020:02:00.0: ACS mask = 0x002c pci 0020:02:00.0: ACS flags = 0xffd3 pci 0020:02:00.0: Configured ACS to 0xfffb pci 0030:02:00.0: ACS mask = 0x002c pci 0030:02:00.0: ACS flags = 0xffd3 pci 0030:02:00.0: Configured ACS to 0xffdf pci 0039:00:00.0: ACS mask = 0x002c pci 0039:00:00.0: ACS flags = 0xffd3 pci 0039:00:00.0: Configured ACS to 0xffd3 After this fix: Kernel command line: pci=disable_acs_redir=0020:02:00.0;0030:02:00.0;0039:00:00.0 "dyndbg=file drivers/pci/pci.c +p" pci 0020:02:00.0: ACS mask = 0x002c pci 0020:02:00.0: ACS flags = 0xffd3 pci 0020:02:00.0: ACS control = 0x007f pci 0020:02:00.0: ACS fw_ctrl = 0x007b pci 0020:02:00.0: Configured ACS to 0x0053 pci 0030:02:00.0: ACS mask = 0x002c pci 0030:02:00.0: ACS flags = 0xffd3 pci 0030:02:00.0: ACS control = 0x005f pci 0030:02:00.0: ACS fw_ctrl = 0x005f pci 0030:02:00.0: Configured ACS to 0x0053 pci 0039:00:00.0: ACS mask = 0x002c pci 0039:00:00.0: ACS flags = 0xffd3 pci 0039:00:00.0: ACS control = 0x001d pci 0039:00:00.0: ACS fw_ctrl = 0x0000 pci 0039:00:00.0: Configured ACS to 0x0000 Link: https://lore.kernel.org/r/20250207030338.456887-1-tdave@nvidia.com Fixes:47c8846a49("PCI: Extend ACS configurability") Signed-off-by: Tushar Dave <tdave@nvidia.com> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.