linux-kernel - Re: [PATCH V2] VFIO driver: Non-privileged user level PCI drivers

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Date:	Mon, 05 Jul 2010 22:50:05 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Tom Lyon <pugs@...co.com>
Cc:	randy.dunlap@...cle.com, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, chrisw@...s-sol.org, joro@...tes.org,
	hjk@...utronix.de, mst@...hat.com, avi@...hat.com, gregkh@...e.de,
	aafabbri@...co.com, scofeldm@...co.com
Subject: Re: [PATCH V2] VFIO driver: Non-privileged user level PCI drivers

Hi Tom.

A few MSI issues below.  Thanks,

Alex

On Tue, 2010-06-08 at 14:21 -0700, Tom Lyon wrote:
> diff -uprN linux-2.6.34/drivers/vfio/vfio_pci_config.c vfio-linux-2.6.34/drivers/vfio/vfio_pci_config.c
> --- linux-2.6.34/drivers/vfio/vfio_pci_config.c	1969-12-31 16:00:00.000000000 -0800
> +++ vfio-linux-2.6.34/drivers/vfio/vfio_pci_config.c	2010-05-28 14:26:47.000000000 -0700
> +/*
> + * Lengths of PCI Config Capabilities
> + * 0 means unknown (but at least 4)
> + * FF means special/variable
> + */
> +static u8 pci_capability_length[] = {
> +	[PCI_CAP_ID_BASIC]	= 64,		/* pci config header */
> +	[PCI_CAP_ID_PM]		= PCI_PM_SIZEOF,
> +	[PCI_CAP_ID_AGP]	= PCI_AGP_SIZEOF,
> +	[PCI_CAP_ID_VPD]	= 8,
> +	[PCI_CAP_ID_SLOTID]	= 4,
> +	[PCI_CAP_ID_MSI]	= 0xFF,		/* 10, 14, or 24 */

I think this is actually 10, 14, 20, or 24.

> +static struct perm_bits pci_cap_msi_perm[] = {
> +	{ 0,		0, },		/* 0x00 MSI message control */
> +	{ 0xFFFFFFFF,	0xFFFFFFFF, },	/* 0x04 MSI message address */
> +	{ 0xFFFFFFFF,	0xFFFFFFFF, },	/* 0x08 MSI message addr/data */
> +	{ 0x0000FFFF,	0x0000FFFF, },	/* 0x0c MSI message data */
> +	{ 0,		0xFFFFFFFF, },	/* 0x10 MSI mask bits */
> +	{ 0,		0xFFFFFFFF, },	/* 0x14 MSI pending bits */
> +};

Is there any reason for mask bits to have virtualized writes?  I don't
think we can support all 4 MSI capability sizes with this one table.  We
probably need a 32bit and 64bit version, then we can drop the mask,
pending, and reserved fields via the length.

> +		if (len == 0xFF) {
> +			switch (cap) {
> +			case PCI_CAP_ID_MSI:
> +				ret = pci_read_config_word(pdev,
> +						pos + PCI_MSI_FLAGS, &flags);
> +				if (ret < 0)
> +					return ret;
> +				if (flags & PCI_MSI_FLAGS_MASKBIT)
> +					/* per vec masking */
> +					len = 24;
> +				else if (flags & PCI_MSI_FLAGS_64BIT)

These aren't mutually exclusive features aiui.

> +					/* 64 bit */
> +					len = 14;
> +				else
> +					len = 10;
> +				break;

This should probably be something like

len = 10;
if (flags & PCI_MSI_FLAGS_MASKBIT)
    len += 10;
if (flags & PCI_MSI_FLAGS_64BIT) {
    /* set 64bit permission table */
    len += 4;
} else
    /* set 32bit permission table */

> diff -uprN linux-2.6.34/include/linux/vfio.h vfio-linux-2.6.34/include/linux/vfio.h
> --- linux-2.6.34/include/linux/vfio.h	1969-12-31 16:00:00.000000000 -0800
> +++ vfio-linux-2.6.34/include/linux/vfio.h	2010-06-07 12:20:06.000000000 -0700

> +/* request MSI interrupts; use given eventfd */
> +#define	VFIO_EVENTFD_MSI	_IOW(';', 105, int)

Any intention of supporting MSI multiple message capability?  If so,
this might turn into the same interface as MSIX.

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