Re: [PATCH v9 1/6] PCI: Validate ACS control bits against device-specific ACS capabilities

From: Wei Wang

Date: Thu Sep 03 2026 - 09:25:26 EST

On 9/3/26 7:07 PM, Ilpo Järvinen wrote:

On Thu, 3 Sep 2026, Wei Wang wrote:

The ACS control validation used the kernel's full set of ACS control bits,
which allowed users to request ACS features that the device does not
support. Because hardware silently ignores these unsupported bits, users
have no indication that their config_acs= request was partially
ineffective.

Validate the requested ACS control bits against dev->acs_capabilities so
that only device-supported ACS controls are accepted. Mask the capability
with GENMASK_U16(6, 0) to select only the currently defined ACS control
bits (0-6). Higher bits in the capability structure (e.g. the egress
control vector size in bits 8-15) do not correspond to control bits in
the ACS control register. Add a debug message to report which unsupported
bits were ignored.

__pci_config_acs() is also called from disable_acs_redir_param(), which
passes a hardcoded acs_mask (PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_EC) that
does not need validation. Gate the new check on !acs_mask so it only
fires for the config_acs_param path, which always invokes
__pci_config_acs() with acs_mask == 0 and builds the actual mask from
user input.

Also move the check after the device is matched, since the ctrl bits apply
only to the matched device.

Signed-off-by: Wei Wang <wei.w.wang@xxxxxxxxxxx>
Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
---
drivers/pci/pci.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b2879a6be5f8..2af679111a9b 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -910,6 +910,7 @@ struct pci_acs {
static void __pci_config_acs(struct pci_dev *dev, struct pci_acs *caps,
const char *p, const u16 acs_mask, const u16 acs_flags)
{
+ u16 valid_ctrl = dev->acs_capabilities & GENMASK_U16(6, 0);

This looks a step backwards.

These bits are surely named so this mask should be a composite of those
define names, either done here or through another define (likely the
latter is better).