Re: [RESEND PATCH v2] PCI: Fix Extend ACS configurability

Bjorn Helgaas
2025-02-21T22:23:35Z

On Thu, Feb 06, 2025 at 07:03:38PM -0800, Tushar Dave wrote:
> Commit 47c8846a49ba ("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.
>
> First, 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 the bug in code that doesn't
> preserve the ACS mask 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
>
> Second bug is in the bit manipulation logic where 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
>
> Fixes: 47c8846a49ba ("PCI: Extend ACS configurability")
> Signed-off-by: Tushar Dave <tdave@nvidia.com>

Applied to pci/acs for v6.15, thanks!

> ---
>
> changes in v2:
> - Addressed review comments by Jason and Bjorn.
> - Removed Documentation changes (already taken care by other patch).
> - Amended commit description.
>
> drivers/pci/pci.c | 17 ++++++++++++-----
> 1 file changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 869d204a70a3..c1ab5d50112d 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -954,8 +954,10 @@ struct pci_acs {
> };
>
> static void __pci_config_acs(struct pci_dev *dev, struct pci_acs *caps,
> - const char *p, u16 mask, u16 flags)
> + const char *p, const u16 acs_mask, const u16 acs_flags)
> {
> + u16 flags = acs_flags;
> + u16 mask = acs_mask;
> char *delimit;
> int ret = 0;
>
> @@ -963,7 +965,7 @@ static void __pci_config_acs(struct pci_dev *dev, struct pci_acs *caps,
> return;
>
> while (*p) {
> - if (!mask) {
> + if (!acs_mask) {
> /* Check for ACS flags */
> delimit = strstr(p, "@");
> if (delimit) {
> @@ -971,6 +973,8 @@ static void __pci_config_acs(struct pci_dev *dev, struct pci_acs *caps,
> u32 shift = 0;
>
> end = delimit - p - 1;
> + mask = 0;
> + flags = 0;
>
> while (end > -1) {
> if (*(p + end) == '0') {
> @@ -1027,10 +1031,13 @@ static void __pci_config_acs(struct pci_dev *dev, struct pci_acs *caps,
>
> pci_dbg(dev, "ACS mask = %#06x\n", mask);
> pci_dbg(dev, "ACS flags = %#06x\n", flags);
> + pci_dbg(dev, "ACS control = %#06x\n", caps->ctrl);
> + pci_dbg(dev, "ACS fw_ctrl = %#06x\n", caps->fw_ctrl);
>
> - /* If mask is 0 then we copy the bit from the firmware setting. */
> - caps->ctrl = (caps->ctrl & ~mask) | (caps->fw_ctrl & mask);
> - caps->ctrl |= flags;
> + /* For mask bits that are 0 copy them from the firmware setting
> + * and apply flags for all the mask bits that are 1.
> + */
> + caps->ctrl = (caps->fw_ctrl & ~mask) | (flags & mask);
>
> pci_info(dev, "Configured ACS to %#06x\n", caps->ctrl);
> }
> --
> 2.34.1
>