Re: [PATCH v3] xen-pciback: Consider INTx disabled when MSI/MSI-X is enabled

From: Marek Marczykowski-Górecki
Date: Wed Sep 27 2023 - 06:33:16 EST


On Fri, Nov 18, 2022 at 04:49:23PM +0100, Marek Marczykowski-Górecki wrote:
> Linux enables MSI-X before disabling INTx, but keeps MSI-X masked until
> the table is filled. Then it disables INTx just before clearing MASKALL
> bit. Currently this approach is rejected by xen-pciback.
> According to the PCIe spec, device cannot use INTx when MSI/MSI-X is
> enabled (in other words: enabling MSI/MSI-X implicitly disables INTx).
>
> Change the logic to consider INTx disabled if MSI/MSI-X is enabled. This
> applies to three places:
> - checking currently enabled interrupts type,
> - transition to MSI/MSI-X - where INTx would be implicitly disabled,
> - clearing INTx disable bit - which can be allowed even if MSI/MSI-X is
> enabled, as device should consider INTx disabled anyway in that case
>
> Fixes: 5e29500eba2a ("xen-pciback: Allow setting PCI_MSIX_FLAGS_MASKALL too")
> Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>

Ping?

The issue pointed out by Jason was fixed in Xen:
https://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=913751d7af6e78d65c1e2adf4887193c827f0c5e

> ---
> Changes in v3:
> - allow clearing INTx regardless of MSI/MSI-X state, to be consistent
> with enabling MSI/MSI-X
> Changes in v2:
> - restructure the patch to consider not only MASKALL bit, but enabling
> MSI/MSI-X generally, without explicitly disabling INTx first
> ---
> drivers/xen/xen-pciback/conf_space.c | 19 +++++++++++------
> .../xen/xen-pciback/conf_space_capability.c | 3 ++-
> drivers/xen/xen-pciback/conf_space_header.c | 21 +++----------------
> 3 files changed, 18 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/xen/xen-pciback/conf_space.c b/drivers/xen/xen-pciback/conf_space.c
> index 059de92aea7d..d47eee6c5143 100644
> --- a/drivers/xen/xen-pciback/conf_space.c
> +++ b/drivers/xen/xen-pciback/conf_space.c
> @@ -288,12 +288,6 @@ int xen_pcibk_get_interrupt_type(struct pci_dev *dev)
> u16 val;
> int ret = 0;
>
> - err = pci_read_config_word(dev, PCI_COMMAND, &val);
> - if (err)
> - return err;
> - if (!(val & PCI_COMMAND_INTX_DISABLE))
> - ret |= INTERRUPT_TYPE_INTX;
> -
> /*
> * Do not trust dev->msi(x)_enabled here, as enabling could be done
> * bypassing the pci_*msi* functions, by the qemu.
> @@ -316,6 +310,19 @@ int xen_pcibk_get_interrupt_type(struct pci_dev *dev)
> if (val & PCI_MSIX_FLAGS_ENABLE)
> ret |= INTERRUPT_TYPE_MSIX;
> }
> +
> + /*
> + * PCIe spec says device cannot use INTx if MSI/MSI-X is enabled,
> + * so check for INTx only when both are disabled.
> + */
> + if (!ret) {
> + err = pci_read_config_word(dev, PCI_COMMAND, &val);
> + if (err)
> + return err;
> + if (!(val & PCI_COMMAND_INTX_DISABLE))
> + ret |= INTERRUPT_TYPE_INTX;
> + }
> +
> return ret ?: INTERRUPT_TYPE_NONE;
> }
>
> diff --git a/drivers/xen/xen-pciback/conf_space_capability.c b/drivers/xen/xen-pciback/conf_space_capability.c
> index 097316a74126..eb4c1af44f5c 100644
> --- a/drivers/xen/xen-pciback/conf_space_capability.c
> +++ b/drivers/xen/xen-pciback/conf_space_capability.c
> @@ -236,10 +236,11 @@ static int msi_msix_flags_write(struct pci_dev *dev, int offset, u16 new_value,
> return PCIBIOS_SET_FAILED;
>
> if (new_value & field_config->enable_bit) {
> - /* don't allow enabling together with other interrupt types */
> + /* don't allow enabling together with other interrupt type */
> int int_type = xen_pcibk_get_interrupt_type(dev);
>
> if (int_type == INTERRUPT_TYPE_NONE ||
> + int_type == INTERRUPT_TYPE_INTX ||
> int_type == field_config->int_type)
> goto write;
> return PCIBIOS_SET_FAILED;
> diff --git a/drivers/xen/xen-pciback/conf_space_header.c b/drivers/xen/xen-pciback/conf_space_header.c
> index 981435103af1..fc0332645966 100644
> --- a/drivers/xen/xen-pciback/conf_space_header.c
> +++ b/drivers/xen/xen-pciback/conf_space_header.c
> @@ -104,24 +104,9 @@ static int command_write(struct pci_dev *dev, int offset, u16 value, void *data)
> pci_clear_mwi(dev);
> }
>
> - if (dev_data && dev_data->allow_interrupt_control) {
> - if ((cmd->val ^ value) & PCI_COMMAND_INTX_DISABLE) {
> - if (value & PCI_COMMAND_INTX_DISABLE) {
> - pci_intx(dev, 0);
> - } else {
> - /* Do not allow enabling INTx together with MSI or MSI-X. */
> - switch (xen_pcibk_get_interrupt_type(dev)) {
> - case INTERRUPT_TYPE_NONE:
> - pci_intx(dev, 1);
> - break;
> - case INTERRUPT_TYPE_INTX:
> - break;
> - default:
> - return PCIBIOS_SET_FAILED;
> - }
> - }
> - }
> - }
> + if (dev_data && dev_data->allow_interrupt_control &&
> + ((cmd->val ^ value) & PCI_COMMAND_INTX_DISABLE))
> + pci_intx(dev, !(value & PCI_COMMAND_INTX_DISABLE));
>
> cmd->val = value;
>
> --
> 2.37.3
>

--
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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