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

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Date:   Wed, 27 Sep 2023 12:33:05 +0200
From:   Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>
To:     linux-kernel@...r.kernel.org
Cc:     Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Jan Beulich <jbeulich@...e.com>,
        "moderated list:XEN HYPERVISOR INTERFACE" 
        <xen-devel@...ts.xenproject.org>
Subject: Re: [PATCH v3] xen-pciback: Consider INTx disabled when MSI/MSI-X is
 enabled

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@...isiblethingslab.com>

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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